No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Bite dimensions for cattle grazing herbage at low levels of depletion
Abstract
The processes that occur during the depletion of a single feeding station by grazing cattle are important to our understanding of intake at larger spatial scales. Factorial experiments were conducted in which feeding stations of different sizes were grazed individually by cattle to various levels of depletion, defined as the number of bites removed. Feeding stations in Experiment 1 (alfalfa) measured 0·11, 0·24 and 0·45 m ² , and the numbers of bites removed for depletion levels 1–3 were 35, 70 and 104 m ⁻² respectively. Feeding stations in Experiment 2 (oats) measured 0·11 and 0·24 m ² , and the numbers of bites were 45, 95 and 140 m ⁻² offered. In both experiments a fourth depletion level (not included in the analysis of variance) determined the maximum voluntary depletion, and exceeded 250 bites m ⁻² offered. Initial sward height was 20 cm. Bite dimensions were derived from the frequency distribution of residual herbage heights. Treatments were replicated over six and four animals of approximately 500 kg live weight in Experiments 1 and 2 respectively.
The mean residual herbage height and the frequency distribution of residual heights indicated that bites were removed predominantly from the top grazing horizon at depletion levels 1–3, with a mean effective bite depth of 8·6 cm. Nevertheless, at the same depletion levels, the mean effective bite area declined from 148 to 87 cm ² in Experiment 1 (alfalfa, Medicago sativa L.) and from 86 to 58 cm ² in Experiment 2 (oats, Avena sativa L.). Feeding station size did not significantly affect mean effective bite area in either experiment.
Simulation was used to examine the implications of various overlap rules (from completely random to highly systematic) for within‐grazing‐horizon placement of a circular bite of constant potential area. These rules shaped the relationship between mean effective bite area and number of bites removed per unit sward area offered. Bite placement in which permissible overlap became progressively more lenient as the grazing horizon was depleted, and, with acceptable estimates of potential bite area, yielded results that were similar, though not identical, to those measured. These results can help understanding of the factors that determine the intake gain function at a single feeding station.
... There is strong empirical evidence that grazing ruminants employ a horizontal, stratumorientated depletion style at the scale of a single feeding station or ''patch'' (Ungar et al., 1991(Ungar et al., , 2001Ungar and Griffiths, 2002); that is, they remove the majority of bites within the uppermost grazing stratum before penetrating into a lower stratum. Furthermore, during the depletion of a stratum, bite volume (bite depth  bite area) may be less than the potential volume that could be harvested by a single bite. ...
... This decline in effective bite volume has been attributed to increasing overlap in the horizontal plane between the areas swept for herbage in the process of bite formation (Ungar et al., 2001). Why the animal should create such overlap is not clear, since nonoverlapping bites would be expected to yield the highest bite mass and hence the highest intake rate (Laca et al., 1992a). ...
... The bite placement simulator of Ungar and Ravid (1999) suggested that highly systematic bite placement would be required in order to avoid a decline in mean effective bite area. In a further development of the simulator, Ungar et al. (2001) examined four bite placement rules that related the dependence of the mean effective bite area on the level of depletion and thus bite overlap: ...
Bite placement plays an important role in determining the mean weight of bites removed from a patch, and hence intake rate. This paper describes a video and acoustic methodology to map the sequential placement of bites on the sward surface. The methodology was evaluated for dairy heifers grazing small (0.34m2) patches of alfalfa (Medicago sativa L.) to three levels of depletion (6, 18 and 30 bites). Grazing was recorded by a single video camera positioned 0.9m in front of the animal and on average 1.67m above the ground. Acoustic monitoring enabled the precise timing of biting jaw movements (bite or chew-bite). For each bite, a single video frame showing the position of the animal's head in the sward canopy was selected at the point in time corresponding to bite severance. Custom image-processing software was used to extract the image (apparent) coordinates of the tip of the muzzle, which was then converted geometrically to world (true) coordinates on the sward surface. A fixed displacement of 8cm was applied to the world coordinates in order to determine the bite centre. The pattern of grazing impact across the sward surface was predicted by assuming a radius of impact around each bite centre. This pattern was compared with the measured status (grazed or un-grazed) of the herbage beneath each cell of a grid placed over the patch after grazing. Bite placement on the sward surface, as defined by the bite-centre coordinates, followed a progressing, side-to-side pathway. The median distance between the centres of consecutive bites was 12.1cm, and was significantly less than expected by random bite placement. The orientation of consecutive bite pairs differed significantly from random, consistent with the side-to-side pathway of bite placement. Nevertheless, based on nearest neighbour analysis, the overall pattern of bite spacing on the surface of the sward did not differ significantly from random. These results suggest that the observed declining trend in mean effective bite area with increasing depletion (P=0.06) derived from inefficient exploitation of the sward surface. The assumption of a radius of impact of 6cm revealed a broad correspondence between the measured and predicted patterns of grazing impact across the sward surface. Discrepancies most likely reflected sweeping actions of the tongue during bite formation, lateral head movements during bite severance and simplifying assumptions required by the single-camera approach. The results indicate that the methodology is potentially useful for investigating the rules governing bite placement in the horizontal plane.
... strips in rotational stocking), there is a succession of potential bites available in succeeding layers (Ungar 1998; Baumont et al. 2004). Bites are taken progressively from upper layers to the bottom, each succeeding layer constraining bite volume by reducing bite depth and area (Ungar et al. 2001 ). Nutrient concentration in the bite volume decreases as the layer being grazed approaches the soil surface. ...
... Thus pastures can be viewed as sets of superimposed grazing horizons (compartments of bites), with the probability of grazing the lowest horizons increasing as the uppermost layers are progressively grazed (Ungar and Ravid 1999; Baumont et al. 2004). Ungar et al. (2001) described this scenario by observing heifers taking bites from the uppermost grazing horizon, almost exclusively, until approximately three-quarters of its surface area had been removed. Fonseca et al. (2013) registered similar horizon use patterns with different pasture structures under field conditions. ...
Grazing is a fundamental process affecting grassland ecosystem dynamics and functioning. Its behavioral components comprise how animals search for feed, and gather and process plant tissues in different spatio-temporal scales of the grazing process. Nowadays, there is an increasing emphasis on grazing management and the role of the grazing animal on ecosystem services, concomitantly with a decreasing emphasis on grazing management generating animal production outputs. Grazing behavior incorporates both approaches, which are not necessarily dichotomist. It would provide the basis to support innovation in grazing systems. However, it is unclear how the significant knowledge, developed in this research area since the disciplines of Agronomy and Ecology began to interact, have supported creativity in grazing science. It seems there is a current gap in this context, which was a major concern of researcher leaders like Harry Stobbs. This paper pays tribute to him, reviewing recent grazing behavior research and prioritizing those studies originating in the favorable tropics and subtropics. New evidence on how pasture structure limits forage intake in homogeneous and heterogeneous pastures is presented. Pasture management strategies designed to maximize bite mass and forage intake per unit grazing time are assumed to promote both animal production and landscape value. To conclude, a Brazilian case study (PISA) is briefly described to illustrate how grazing behavior research can reach farmers and change their lives by using simple management strategies (“take the best and leave the rest” rule) supported by reductionist approaches applied in holistic frameworks.
... Sward structure is constantly changing as a result of plant growth, defoliation and senescence. In rotational method there is an increase in the bulk density and a decrease in leaf/pseudostem ratio throughout grazing down (Barrett et al., 2001;Ungar et al., 2001). Consequently, there is a progressive reduction in short-term intake rate (Fonseca et al., 2013) and bite area (Ungar et al., 2001), resulting in a daily herbage intake reduction (Barrett et al., 2001;Baumont et al., 2004). ...
... In rotational method there is an increase in the bulk density and a decrease in leaf/pseudostem ratio throughout grazing down (Barrett et al., 2001;Ungar et al., 2001). Consequently, there is a progressive reduction in short-term intake rate (Fonseca et al., 2013) and bite area (Ungar et al., 2001), resulting in a daily herbage intake reduction (Barrett et al., 2001;Baumont et al., 2004). Throughout this process, temperate and tropical pastures may impose different constraints on consumption due to the increased abundance of pseudostems (Griffiths et al., 2003). ...
... strips in rotational stocking), there is a succession of potential bites available in succeeding layers (Ungar 1998;Baumont et al. 2004). Bites are taken progressively from upper layers to the bottom, each succeeding layer constraining bite volume by reducing bite depth and area (Ungar et al. 2001). Nutrient concentration in the bite volume decreases as the layer being grazed approaches the soil surface. ...
... ive preference only. Bite mass is maximized in taller pastures as demonstrated byLaca et al. (1994). Thus pastures can be viewed as sets of superimposed grazing horizons (compartments of bites), with the probability of grazing the lowest horizons increasing as the uppermost layers are progressively grazed (Ungar and Ravid 1999;Baumont et al. 2004).Ungar et al. (2001)described this scenario by observing heifers taking bites from the uppermost grazing horizon, almost exclusively, until approximately three-quarters of its surface area had been removed.Fonseca et al. (2013)registered similar horizon use patterns with different pasture structures under field conditions.Figure 10presents the changes in th ...
Grazing is a fundamental process affecting grassland ecosystem dynamics and functioning. Its behavioral components comprise how animals search for feed, and gather and process plant tissues in different spatio-temporal scales of the grazing process. Nowadays, there is an increasing emphasis on grazing management and the role of the grazing animal on ecosystem services, concomitantly with a decreasing emphasis on grazing management generating animal produc-tion outputs. Grazing behavior incorporates both approaches, which are not necessarily dichotomist. It would provide the basis to support innovation in grazing systems. However, it is unclear how the significant knowledge, developed in this research area since the disciplines of Agronomy and Ecology began to interact, have supported creativity in graz-ing science. It seems there is a current gap in this context, which was a major concern of researcher leaders like Harry Stobbs. This paper pays tribute to him, reviewing recent grazing behavior research and prioritizing those studies origi-nating in the favorable tropics and subtropics. New evidence on how pasture structure limits forage intake in homogeneous and heterogeneous pastures is presented. Pasture management strategies designed to maximize bite mass and forage intake per unit grazing time are assumed to promote both animal production and landscape value. To con-clude, a Brazilian case study (PISA) is briefly described to illustrate how grazing behavior research can reach farmers and change their lives by using simple management strategies ("take the best and leave the rest" rule) supported by reductionist approaches applied in holistic frameworks.
... 012– 0 . 022 m 2 (Ungar et al., 2001). The potential BM within the grazed strata during a virtual vertical depletion of a homogeneous feeding station was estimated using the concepts developed by Ungar et al. (1992). ...
... 6 m 2 in this study). Such large virtual canopies can then be used to test bite placement modelling (Ungar et al., 2001) and enable the use of a broad range of different geometric volumes to simulate the actual bite form, as well as overlapping rules to assess different depletion patterns. The present findings show that BM and LIE after grazing are clearly dependent on bite form, even for a similar bite area and depth. ...
Background and Aims The productivity and stability of grazed grassland rely on dynamic interactions between the sward and the animal. The descriptions
of the sward canopies by standard 2-D representations in studies of animal–sward interactions at the bite scale need to be
improved to account for the effect of local canopy heterogeneity on bite size and regrowth ability. The aim of this study
was to assess a methodology of 3-D digitized canopies in order to understand the balance between bite mass and light interception
by the residual sward.
... In vegetative swards, bite area was not related to sward height which disagrees with previous studies where bite area increased with sward height (Cangiano et al., 2002;Flores et al., 1993;Laca et al., 1992;Ungar et al., 2001). In tall swards the animal can fully exploit the benefits of the tongue sweep movements to gather forage and thus the animal can achieve the maximum bite area. ...
... The lack of response of bite area to sward height in vegetative swards in the current work can be explained in part by the relatively small body mass of the animals used in this experiment, whose bite area is less sensitive to the increase in sward height than that of bigger animals (Gordon 1987), and by the significant correlation between sward height and grazing resistance (r = 0.88, P b 0.001). Therefore, the positive relationship between bite area and sward height (Cangiano et al., 2002;Flores et al., 1993;Laca et al., 1992;Ungar et al., 2001) could have been compensated by the negative relationship between bite area and sward grazing resistance (Illius et al., 1995) resulting in the observed lack of effect of sward height on bite area of the current experiment. ...
The rate of nutrient intake (RNI) is a primary determinant of animal performance in grazing cattle and depends on both diet quality and instantaneous intake rate (IIR). In turn, diet quality and IIR are a function of the foraging behaviour of the animal (selectivity, bite mass and bite rate) and the characteristics of the sward. In this study we evaluated the effect of the stem density and the tensile resistance of stems on the foraging behaviour of cattle grazing tropical pasture species. The methodology involved the use of small sown microswards offered to tethered cattle. The experiment consisted of a factorial combination of five tropical grasses [Bothriochloa pertusa (Bp), Chloris barbata (Cb), Chloris gayana (Cg), Cynodon dactylon (Cd) and Heteropogon contortus (Hc)] and three stem densities (0, 400 and 800 stems m(-2)). Bp and Cd had stems of significantly lower tensile resistance (19 and 15 N respectively) (Group 1) than those of Cb, Cg and Hc (110, 211 and 167 N respectively) (Group 2). The steers avoided stems of Group 2 and thus, reduced bite area, bite mass, IIR and RNI as stem density increased. However, the animals did not avoid stems of Group 1 and there was no effect of stem density on any of the foraging behaviour variables when cattle grazed species in Group 1. These results confirm that RNI and plant part selection is closely associated with the tensile resistance of the stem.
... These differences can be attributed to the different tiller densities between the studies (>2000 tillers m À2 in the present study vs. 808 tillers m À2 in Hongo, 1998), suggesting that animals in our study repeatedly took herbage from the same area in the swards because of the high tiller and bulk density. Note that grazing ruminants mostly bite the upper stratum in grazing swards before reaching a lower stratum (Griffiths et al., 2006;Ungar et al., 1991Ungar et al., , 2001, and grazing in the vertical direction requires extra effort. Previous studies (Benvenutti et al., 2006(Benvenutti et al., , 2009 showed that the bite dimension and bite mass of cattle decreased with the increase in stem density in grasses of high tensile resistance, but no effect of stem density was detected on these bite parameters when cattle grazed grasses of low tensile resistance. ...
This study aimed to clarify the differences in ingestive behavior between goats and sheep at the bite scale. Animals were allowed to graze a feeding station of bahiagrass (Paspalum notatum Flügge) with two sward heights (short and tall) to two levels of bite depletion (20 and 40 bites). Ingestive behavior variables, which represent the rate and mass of bites and chews, intake rate, bite dimensions, and bite placement characteristics, were quantified. The interspecies difference in ingestive behavior became obvious at the short sward. Goats reduced the inter-bite distance and maintained bite overlapping but took deeper bites than sheep at the short sward, resulting in slightly greater bite mass. These behavioral changes with efficient chewing may be helpful to maintain the intake rate at the short sward. Sheep maintained their inter-bite distance regardless of the sward height and decreased overlapping bites at the short sward. These behavioral characteristics in sheep in response to sward height may partly compensate for the decrease in the bite mass at the short sward, although it may not always maintain the intake rate. Thus, the present study suggests that goats and sheep implement different bite scale ingestive behaviors, including bite placement, when they eat short swards.
... Our results also demonstrated the importance of the proportion of the pasture area ungrazed for the grazing behaviour, once sheep exhibit a partial preference by previously ungrazed plants (Fig. 6), affecting bite mass directly. Similarly, previous studies have reported that forage intake decreases when the upper stratum is removed due to a limitation for grazers to form large bites (Ungar and Ravid 1999;Ungar et al. 2001;Benvenutti et al. 2016). Therefore, to develop management guidelines that have more predictable intake responses, the concept of heterogeneity must be fully incorporated into grazing science. ...
Context: Average sward height has traditionally been used as a grazing management variable. However, such approach ignores the spatio-temporal heterogeneity of swards. Because the intake rate responds non-linearly to average height at plant level, we expected that sheep exposed to contrasting grazing methods with similar average heights would behave differently.
Aims: We hypothesised that low-intensity, high-frequency grazing results in a higher daily intake rate than does high-intensity, low-frequency grazing, despite both methods having similar average sward heights over space and time. Also, we asked whether sheep exhibit the same foraging mechanisms for a given instantaneous sward state regardless of long-term grazing conditions imposed.
Methods: We exposed sheep to two contrasting grazing methods with similar average height; low-intensity, high-frequency (LIHF), and high-intensity, low-frequency (HILF). We then evaluated their foraging behaviour using continuous bite-monitoring paired with detailed sward measurements during grazing down.
Key results: Sward height decreased markedly during the grazing period in both treatments, but the sward height depletion was faster under HILF (7.5 cm and 20.3 cm for LIHF and HILF), which means that sward structure was severely disrupted. The animals exhibited markedly different herbage intake patterns between the grazing methods, with sheep under LIHF presenting greater total daily herbage intake (850 vs 630 g DM per individual). Also, sheep demonstrated a more stable and higher instantaneous intake rate in the LIHF. Despite the difference in total daily herbage intake, the grazing treatments did not affect the behavioural mechanisms beyond their indirect effects on the rate of change in the instantaneous sward conditions. Grazing treatments created different patterns of sward change and intake rate over time, but the local and instantaneous sward conditions determined intake rate regardless of the grazing method.
Conclusions: Intake responses of sheep differed between grazing methods with similar average height due to sward heterogeneity over time and space. Grazing mechanisms were not directly affected by the treatments but were influenced by the sward heterogeneity imposed by the grazing management.
Implications: Grazing management requires not only consideration of the average sward height, but also an understanding of how the resource is distributed in time and space.
... However, the reduction in bite rate (Table 3) shows a change in the time of apprehension and manipulation process of stems and inflorescences to maintain a constant daily forage intake until the final grazing down stage (Benvenutti et al., 2015). As observed in studies that aimed to understand what occurs during grazing down (Amaral et al., 2012;Laca et al., 1992;Ungar et al., 2001), the sward structural modifications between the grazing strata (a decrease in the leaf/stem ratio) interfere negatively in the herbivores' ingestive behavior, considering the progressive decrease in the bite mass and in the herbage intake rate. ...
Foraging behavior studies have supported innovations in sward management, making pastoral systems more sustainable and competitive. Based on this, we evaluated the sheep's ingestive behavior responses and the changes in sward structure during four stages of grazing down in rotational stocking, indicating the threshold level of grazing down for sheep grazing in the reproductive stage of annual ryegrass (Lolium multiflorum Lam.) managed under two grazing intensities (low and moderate). We found evidence that the two grazing intensities each promoted a grazing down at approximately 45% of the non-limiting pre-grazing sward height. However, during grazing down at the end of the sward reproductive stage, the leaves frequency remained lower than that of inflorescences, indicating a restrictive situation for animals in each of the two grazing intensities evaluated. The sheep's ingestive behavior patterns were constrained by the modifications in sward structure. There was observed a decrease in grazing time and bite rate, and a gradual increase in the number of steps between feeding stations during the grazing down stages. Therefore, sheep's behavioral responses during the grazing down of annual ryegrass depend on: (i) grazing intensity, (ii) period of the sward reproductive stage, and (iii) forage structural and chemical composition during grazing down.
... The spatial characteristics of foraging are determined by volume of the available forage and the resource mass contained within that volume. For example, at the bite scale, bite mass is determined by bite volume and the bulk density of the herbage in that volume (Ungar et al. 2001). According to Clutton-Brock and Harvey (1983) and Owen-Smith (1985), bite mass should scale linearly with intradental mouth volume. ...
We investigated whether mass and morphological spatial patterns in plants possibly induced the development of enlarged soft mouth parts in especially megaherbivores. We used power functions and geometric principles to explore allometric relationships of both morphological and foraging characteristics of mammalian herbivores in the South African savannah, covering a body size range of more than three orders magnitude. Our results show that, although intradental mouth volume scaled to a power slightly less than one to body mass, actual bite volume, as measured in the field, scaled to body mass with a factor closer to 1.75. However, when including the volume added to intradental mouth volume by soft mouth parts, such as tongue and lips (or trunks in elephant), mouth volume scaled linearly with actual bite volume and in a similar fashion as actual bite volume to body size. Bite mass and bite leaf mass scaled linearly with body size. We conclude that these scaling relationships indicate that large herbivores use their enlarged soft mouth parts to not only increase bite volume and thereby bite mass, but also select soft plant parts and thereby increase the leaf mass fraction per bite.
... In this context, Ungar et al. (2001) and Cangiano et al. (2002) showed that cattle graze in successive strata that are approximately equivalent to one-half of the SSH, and the removal of these strata reduces bite depth. Therefore, it can be inferred that, at up to 30 cm (above 39 HD), the heifers had not yet reached the grazing stratum with more proportion of stems + sheaths; they still had access to the leaf lamina. ...
... This finding corroborates the results obtained by Searle et al. (2005) who argued that BM is constant within each grazing stratum. In this context, Cangiano et al. (2002) and Ungar et al. (2001) showed that cattle graze in successive strata that are approximately equivalent to half of the SSH, and the removal of these strata reduces bite depth. Therefore, it can be inferred that, at up to 30 cm (above 39 HD), the heifers had not yet reached the grazing stratum with more proportion of stems + sheaths; they still had access to the leaf lamina (Table 2). ...
... This finding corroborates the results obtained by Searle et al. (2005) who argued that BM is constant within each grazing stratum. In this context, Ungar et al. (2001) and Cangiano et al. (2002) showed that cattle graze in successive strata that are approximately equivalent to half of the SSH, and the removal of these strata reduces bite depth. Therefore, it can be inferred that, at up to 30 cm (above 39 HD), the heifers had not yet reached the grazing stratum with more proportion of stems + sheaths; they still had access to the leaf lamina. ...
... In this context, Ungar et al. (2001) and Cangiano et al. (2002) showed that cattle graze in successive strata that are approximately equivalent to one-half of the SSH, and the removal of these strata reduces bite depth. Therefore, it can be inferred that, at up to 30 cm (above 39 HD), the heifers had not yet reached the grazing stratum with more proportion of stems + sheaths; they still had access to the leaf lamina. ...
To maximize herbage dry matter intake (DMI), pre-grazing sward surface height (SSH) and level of herbage depletion (HD) must be such that variables determining short-term herbage intake such as bite mass (BM) and bite rate (BR) are optimized. The objective of this study was to determine a SSH target and the level of HD as a proportion of the SSH that optimizes BM and BR of beef heifers grazing Sorghum bicolor swards. Two experiments were conducted using two S. bicolor swards and four beef heifers (25 mo old, 322 kg body weight [BW]). Experiment 1 compared the effect of six pre-grazing SSH, 30, 40, 50, 60, 70 and 80 cm on BM, BR and jaw movements. Experiment 2 assessed the effect of HD level as a proportion of SSH (0.17, 0.34, 0.50, 0.67 and 0.84) on BM, BR and jaw movements using the optimal pre-grazing SSH defined in Experiment 1. Short-term herbage DMI was estimated using a double-weighing technique and corrected for insensible weight loss. Herbage DMI was subsequently used to calculate the BM. Net eating time and jaw movements for apprehension and manipulation + mastication while grazing, as well as total jaw movements were determined using the IGER behavior recorders. BR and the number of total jaw movements per g herbage DMI were derived from jaw movement count and measurements of herbage DMI. The results of Experiment 1 showed low and high SSH constraint the ease of herbage harvesting. Greater BM are maintained until a SSH of 50 cm is reached (P < 0.05), then declining at greater SSH due to herbage dispersion. The non-biting jaw movement rate increased at greater SSH, whereas BR decreased (P < 0.05). For both variables, the turning point was close to a SSH of 50 cm. Experiment 2 showed that such an optimization of BM and BR was maintained until an HD level of 0.34 was reached (P < 0.05). There was a linear increase in both the total jaw movements per unit herbage DMI and the non-biting jaw movements rate (manipulation + mastication) subsequent to levels of HD greater than 0.34 (P < 0.05). These studies provide, for the first time, sward feature targets to manage grazing and optimize BM and BR, aiming to maximize the short-term herbage DMI of cattle grazing S. bicolor swards.
... If animals do behave in such a way, they must be able to gather and interpret information about their environment in order to modify their grazing behaviour to increase the rate of reward (Bailey et al., 1996). Studies on grazing behaviour by sheep, cattle and horses (Black and Kenney, 1984;Laca et al., 1992;Ungar and Ravid, 1999;Ungar et al., 2001;Illius et al., 1992;Naujeck and Hill, 2003) showed that they discern differences in grass height and that they increased bite dimensions with increasing grass height. To maximize voluntary intake, foraging models suggest that herbivores should select from tall, rather than short, grass. ...
Foraging herbivores are often faced with spatial and temporal heterogeneity within the vegetation they have available to graze and therefore have to make decisions where and when to graze. The study reported in this paper investigated the influence of sward height on diet selection by horses grazing perennial rye-grass swards. The study comprised two experiments. In Experiment 1, perennial rye-grass paddocks were mown to four sward heights (heights: 3.5, 4.5, 7.5 and 15cm) to create a patchy environment. Within each paddock one horse grazed for a period of 1h during which residence time, number of bites and frequency of visits per patch were recorded. This was replicated with all seven horses used in the experiment. The same experiment was repeated in Experiment 2, but without mowing the field and allowing 1 week of re-growth for each paddock. During both experiments horses entered equally often but resided significantly longer on patches with long grass (15cm) than on those with short grass (below 4.5cm; P < 0.05). Grazing time and number of bites on a patch were highly correlated. The number of bites on patches with the highest sward height was greater than that on short patches (P < 0.05). Horses behaved as selective grazers, feeding mainly on grass taller than 7cm. In Experiment 2, re-growth of the sward reduced the difference in sward height between the patches. Time spent per patch and total numbers of bites taken were less affected by sward height than in Experiment 1. It is suggested that horses behaved as energy maximisers (residing longer periods on patches and increasing number of bites taken). These data complement previous findings that bite dimension and bite mass increase with increasing sward height. When grazing, a horse rarely resided on a preferred patch for a long duration of time (maximum 305s, median 79s), but moved on after a few minutes. They sampled their environment continuously, but almost exclusively returned to long patches for feeding.
... The sequence of microswards was completely randomized for each steer on each day and the sequence of six steers was completely randomized within a day. During the experiment, the steers were allowed to take eight bites from the microsward to minimize the effect of overlapping of bites, as the models of Ungar et al. (2001) predicted a slight reduction in bite area, as compared with an undepleted sward, when 0AE30 of the total sward surface area was grazed. ...
The effects of stem density of tropical swards and age of cattle on their foraging behaviour were evaluated using artificial microswards, consisting of leaves of 20 cm in height and high tensile-resisting stems of 25 cm in height of Panicum maximum. The treatments consisted of a factorial combination of four stem densities of swards (0, 100, 200 and 400 stems m−2) and two ages of cattle (1- and 3-year-old steers). There was a significant interaction between stem density of sward and age of cattle for bite area (BA), bite mass (BM) and instantaneous intake rate (IIR). Stem density had a significant negative effect on these variables describing ingestive behaviour which was particularly strong for older steers. In leaf-only swards, mature cattle achieved a much greater BA (106·5 vs. 57·9 cm2), BM (0·88 vs. 0·47 g DM) and IIR (46·9 vs. 17·2 g DM min−1) than did young cattle. However, these variables were very similar across ages of cattle at the highest stem density of sward. These results show the importance of the high tensile-resisting stems as deterrents of the grazing process in tropical pastures, particularly in older cattle.
... Estas decisões podem ser consideradas como uma troca entre os custos e benefícios que a forragem pode oferecer e tem efeito de curta ou longa duração no bem-estar animal (BAILEY et al., 1996). Estudos a respeito do comportamento ingestivo de ovinos, bovinos e eqüinos (ILLIUS et al., 1992; LACA et al., 1992; UNGAR & RAVID, 1999; UNGAR et al., 2001; NAUJECK & HILL, 2003; DITTRICH et al., 2005) mostraram que os animais podem identificar inúmeras características estruturais das plantas, como a altura, a densidade, presença de folhas e colmos etc., e executar diferentes estratégias para a seleção e colheita da forragem. O comportamento dos eqüinos em pastejo e a seleção da dieta são de fundamental importância na avaliação do sistema alimentar na criação de cavalos , porque determinam a quantidade e a qualidade dos nutrientes ingeridos (MICOL et al., 1997; DURANT et al., 2004). ...
Investigou-se o comportamento de eqüinos em pastejo de dosséis compostos por quatro espécies, em experimento desenvolvido na fazenda experimental da Universidade Federal do Paraná, no mês de abril de 2000. Os dosséis foram assim compostos: tifton 85 em mistura com o trevo branco e o cornichão; tifton 85, trevo branco e cornichão em faixas; paspalum em mistura com o trevo branco e o cornichão; paspalum, trevo branco e cornichão em faixas. Marcaram-se quarenta plantas de cada espécie, em cada dossel. Nas gramíneas, mediu-se a altura estendida e nas leguminosas quantificou-se o número de folhas. Doze eqüinos (250 kg) pastejaram a área durante cinco dias. A preferência entre os dosséis foi por localização dos animais e quantificação do tempo em pastejo e pela desfolha em plantas marcadas. Observou-se maior preferência pelos dosséis em mistura, sendo o tifton 85 o preferido, seguido pelo trevo branco e paspalum. Os eqüinos preferiram as maiores gramíneas e o trevo com maior número de folhas. As regressões da altura dos perfilhos e a profundidade do bocado nas gramíneas não apresentaram diferenças (P>0,05). Os eqüinos preferem o pastejo em dosséis onde há mistura de gramíneas e leguminosas e as espécies tifton 85 e trevo branco.
PALAVRAS-CHAVE: Comportamento de pastejo, estrutura de pastagem, eqüinos, gramíneas, leguminosas, seleção de dieta.
... The spatial characteristics of foraging are determined by volume of the available forage and the resource mass contained within that volume. For example, at the bite scale, bite mass is determined by bite volume and the bulk density of the herbage in that volume (Ungar et al. 2001). According to Clutton-Brock and Harvey (1983) and Owen-Smith (1985), bite mass should scale linearly with intradental mouth volume. ...
... Estas decisões podem ser consideradas como uma troca entre os custos e benefícios que a forragem pode oferecer e tem efeito de curta ou longa duração no bem-estar animal (BAILEY et al., 1996). Estudos a respeito do comportamento ingestivo de ovinos, bovinos e eqüinos (ILLIUS et al., 1992; LACA et al., 1992; UNGAR & RAVID, 1999; UNGAR et al., 2001; NAUJECK & HILL, 2003; DITTRICH et al., 2005) mostraram que os animais podem identificar inúmeras características estruturais das plantas, como a altura, a densidade, presença de folhas e colmos etc., e executar diferentes estratégias para a seleção e colheita da forragem. O comportamento dos eqüinos em pastejo e a seleção da dieta são de fundamental importância na avaliação do sistema alimentar na criação de cavalos , porque determinam a quantidade e a qualidade dos nutrientes ingeridos (MICOL et al., 1997; DURANT et al., 2004). ...
Investigou-se o comportamento de eqüinos em pastejo de dosséis compostos por quatro espécies, em experimento desenvolvido na fazenda experimental da Universidade Federal do Paraná, no mês de abril de 2000. Os dosséis foram assim compostos: tifton 85 em mistura com o trevo branco e o cornichão; tifton 85, trevo branco e cornichão em faixas; paspalum em mistura com o trevo branco e o cornichão; paspalum, trevo branco e cornichão em faixas. Marcaram-se quarenta plantas de cada espécie, em cada dossel. Nas gramíneas, mediu-se a altura estendida e nas leguminosas quantificou-se o número de folhas. Doze eqüinos (250 kg) pastejaram a área durante cinco dias. A preferência entre os dosséis foi por localização dos animais e quantificação do tempo em pastejo e pela desfolha em plantas marcadas. Observou-se maior preferência pelos dosséis em mistura, sendo o tifton 85 o preferido, seguido pelo trevo branco e paspalum. Os eqüinos preferiram as maiores gramíneas e o trevo com maior número de folhas. As regressões da altura dos perfilhos e a profundidade do bocado nas gramíneas não apresentaram diferenças (P>0,05). Os eqüinos preferem o pastejo em dosséis onde há mistura de gramíneas e leguminosas e as espécies tifton 85 e trevo branco.
PALAVRAS-CHAVE: Comportamento de pastejo, estrutura de pastagem, eqüinos, gramíneas, leguminosas, seleção de dieta. Horse preference among four swards was investigated at Federal University of Paraná, on April, 2000. Swards were compounded by Cynodon spp (tifton 85) with Trifolium repens (white clover) and Lotus corniculatus (lotus) in mixture, Paspalum paniculatum (paspalum) in mixture with same legumes, Cynodon spp (tifton 85) with same legumes in side by side strip and Paspalum paniculatum (paspalum) with same legumes in side by side strip. The treatments were allocated in 4 randomized blocks. In each plot, ten plants by species were identified. Height extended of each tiller were measured and legume leaves were counted. Twelve horses (250 kg) were distributed on the blocks and kept during the days of experiment. The preference was evaluated through the largest staying time between the treatments and by grazed tillers. Mixture swards were preferred. The treatments with tifton 85 were preferred, idependent if they were in mixture or strip. Among pure species the preference was the following: tifton 85, white clover, paspalum. The lotus was not preferred. Horses grazed the higher tiller in the grasses and for white clover, plants with more leaves. Measures after grazing in tifton 85 and paspalum showed a linear relationship between tiller height and bite depth.
KEY WORDS: Behaviour, diet selection, grasses, horses, legumes.
... The sequence of treatments was randomized within steers. During the experiment, the steers were allowed to take eight bites from the microsward, which was expected to have a minor effect on the overlapping of bites, as the models of Ungar et al. (2001) predicted a slight reduction in bite area compared with an undepleted sward, when 0AE30 of the total sward surface area has been grazed. Foraging behaviour was recorded using a digital video camera with a wired microphone set up next to the microsward. ...
in reproductive swards, stems appear to act as vertical or horizontal barriers to bite formation, influencing instantaneous intake rate (IIR). The hypothesis was tested that the stems' barrier effect is determined by the physical properties and density of stems. Artificial microswards, consisting of 20-cm leaves and 15-cm stems of Panicum maximum, were offered to three steers (362 kg) in a factorial combination of three stem densities (0, 100 and 400 stems m(-2)) and two levels of stem tensile resistance [low (LTRS) and high tensile-resisting stems (HTRS)]. LTRS were not a barrier to defoliation and did not affect bite depth and bite mass. HTRS acted as both a horizontal barrier and a vertical barrier depressing bite depth (13.4, 13.6 and 5.1 cut for 0, 100 and 400 stems m(-2), respectively), bite area (89.3, 50.8 and 47.6 cm(2) for 0, 100 and 400 stems M-2, respectively), bite mass (0.51, 0.29 and 0.11 g for 0, 100 and 400 stems m(-2), respectively) and IIR (23.8, 10.5 and 3.6 g sec(-2) for 0, 100 and 400 Stems m(-2), respectively). The results confirmed the importance of the density and physical properties of stems as determinants of the stems' barrier effect on bite dimensions and IIR.
... The spatial characteristics of foraging are determined by volume of the available forage and the resource mass contained within that volume. For example, at the bite scale, bite mass is determined by bite volume and the bulk density of the herbage in that volume (Ungar et al. 2001). According to Clutton-Brock and Harvey (1983) and Owen-Smith (1985), bite mass should scale linearly with intra-dental mouth volume. ...
Variation in body mass allows for resource partitioning and co-existence of different species. Body mass is also seen as the main factor governing nutrient requirements in herbivores as metabolic rate and requirements have often been found to scale to ¾ power of body mass. Although the consequences of body mass on foraging behaviour of herbivores has been extensively studied, the mechanism behind how body mass differences determines the small scale foraging patterns of especially larger herbivores, has up to now been unclear. In this study, I looked at how body mass and small scale vegetation characteristics shaped the mouth morphology of herbivores and how body mass of a herbivore affects the scale at which intake is maximized. The results indicate that the dilution of plant mass and more specifically leaf mass in space requires that mega-herbivores such as elephant have enlarged soft mouth parts to compensate for this dilution. Finally, I demonstrate, using linear programming techniques with multiple nutrients as constraints, how a mega-herbivore’s daily diet choice is determined by forage abundance whereas a small herbivore is more constrained by fibre.
... Cette limite forme le « grain » de la hiérarchie du pâturage. L'échelle de la bouchée a été couramment utilisée pour étudier les déterminants de la vitesse d'ingestion au pâturage (Ungar, 1996 ;Ungar et Ravid, 1999 ;Ungar et al., 2001), en la décomposant en de nombreux paramètres (surface, profondeur, masse, temps). ...
Extensive management of grassland is an alternative way of abandoning certain areas, but it leads to a spatio-temporal heterogeneity of sward, both in quality and quantity. Our aim was to determine how animal behaviour and sward dynamic would explain the development of this heterogeneity and its spatial organisation. We analysed this development of heterogeneity in relation with intake and behaviour of animals, by making ewes graze continuously two cocksfoot swards at either a high or a low stoking rate (experiment 1). The ewes modified their behaviour at bite and feeding station scales and adapted their movements between patches so as to maximize their diet quality. From ear emergence grazing paths were not randomly performed and were organized around a specific scale of 5 meters. From flowering, on sward with low stocking rate, this behaviour led to a positive feedback resulting in a more frequent grazing of the best quality patches. Sward variability was organised at a macro and micro-heterogeneity, but no specific scale of spatial organization could be identified. We then analysed the role of grazing severity and frequency on sward differentiation and sheep preferences between swards (experiment 2). Sward differentiation was mainly influenced by the overall grazing pressure. Sheep preferences were explained by the relative abundance of green leaves in swards and by grazing frequency. Results are discussed in both a temporal and spatial perspectives and in relation with theoretical models of sward heterogeneity development.
Along with domestication, various changes in nutrition and digestion have occurred in horses as well as in all species. Our review aims to compile existing studies examining the role of nutrition and digestion in the emergence of undesirable behaviours in domestic horses. The success achieved in species with high adaptability has not been sustained by the change in breeding purposes over the years. Welfare, defined as the physical and mental health of animals. The responses of animals to various stimuli are defined as behaviour. Since the behaviour of animals plays a primary role in monitoring welfare, studies on animal behaviour have intensified. The development of undesirable behaviours complicates the care and management practices and negatively affects the welfare of the animals in the following periods, resulting in negative consequences for both the animal and its environment. Stereotypes, which are among the unwanted behaviours and exhibited in the form of purposeless, repetitive movements, are one of the biggest behavioural problems of horse breeding. Oral stereotypes impede food intake, locomotor stereotypes impede mobility and are instrumental in the emergence of chronic and more complex health problems. Other undesirable behaviours may also harm the horse's keeper and other horses kept together in the same box, resulting in serious injury. It is known that nutrition and nutrients affect the development of undesirable behaviours in horses. It is known that anticipatory behaviour creates a basis for repetitive behaviours as a result of inhibition when feeding time and nutrient content are out of preference or insufficient. The effect of nutrition and nutrient content on the emergence of stereotypes and undesirable behaviours has not been fully addressed and the subject remains up-to-date. The purpose of this paper is to provide a brief discussion of studies conducted to assess the effect of nutritional imbalances on stereotypic behaviour in horses. The PRISMA 2020 guidelines were applied to the review using systematic review rules.
Ingestive behaviour determines the nutrient intake and thus feed efficiency and robustness of ruminants through their ability to adapt to diverse available resources. Grazing behavior of ruminant has been intensively researched, but it is still difficult to get a clear picture of the various relationships linking bite mass to daily intake. To address this issue, we led a meta-analysis (103 publications, 278 experiments) to shed light on the quantitative adaptive feeding behaviour responses of cattle (C) and small ruminants (SR) facing variations in sward characteristics, notably sward height (SH, 18. 7 ± 13.9 cm) and herbage bulk density (HBD, 1.73 ± 1.30 kg DM/m³). All responses plotted as a plateau expressing an adaptive limit with extreme SH and HBD values. The minimum plateau for bite rate (BR, 46.9 ± 14.6 min-1) was around 40 min-1, while intake rate (IR) values, different for C and SR, i.e. 69.1 ± 38.1 vs. 99.9 ± 45.7 mg DM/min/kg Body Weight (BW) respectively ranged between a minimum plateau of 50 mg DM/min/kg BW and a maximum plateau around 100 mg DM/min/kg BW. Two other pasture management factors affected IR: herbage allowance (10.16 ± 6.0, DM % BW) and daily proportion of time spent grazing (0.30 ± 0.08). Our results confirm the specific key influence of bite mass (BM, 1.80 ± 127 mg DM/kg BW) on IR. The regressions were IR = 145 (1-exp (-b BM)), where b was 0.44 for C and SR vs. 0.54 for C. This meta-analysis also revealed fundamental differences in behaviour between C and SR that no study to date has attempted to compare. SR have to chew more (2.7 ± 1.2 vs. 1.6 ± 0.5 J M/bite) to ingest the same amount of DM per bite (expressed in relation to BW) as C, which allows them to ingest slightly quicker.
This study assessed the use of pasture attributes to control daily intake and diet quality during progressive defoliation on pastures of Axonopus catarinensis. Three consecutive 12-day grazing treatments of progressive defoliation were conducted with Brahman cross-steers. Daily forage intake and defoliation dynamics were assessed using a pasture-based method. The treatments differed in initial sward height (33, 44 and 61 cm) and herbage mass (1030, 1740 and 2240 kg ha−1). The post-grazing residual sward height, at which forage intake decreased, appeared to increase with the initial sward height (12·3, 14·6 and 15·5 cm). Steers grazed up to four distinctive grazing strata in all treatments. The depth and herbage mass content of the top grazing stratum were at least five times higher than the lower grazing strata in all treatments. This explains why forage intake decreased when the top grazing stratum was removed in approximately 93% of the pasture area in all treatments, equivalent to approximately 7% of the pasture area remaining ungrazed. We conclude that the residual ungrazed area of the pasture, rather than residual sward height, can be used to develop grazing management strategies to control forage intake and diet quality in a wide range of pasture conditions.
The management of pastures used by horses poses various problems: swards are often grazed down rapidly, patches of bare ground and refused areas develop. In order to gain a better understanding of the plant-animal interaction behind this problem the influence of sward height on bite dimensions (bite depth, weight, volume, area) of horses was investigated. Perennial ryegrass (Lolium perenne) microswards were grown on artificial substrate to four different heights (3, 8, 15, 19 cm) but the same plant density. Biomass and bulk density for each sward height was determined. Eight horses (predominantly Thoroughbred ×) were allowed to take six bites of each grass height. Bite depth, weight, volume and bite area were calculated.
Bite depth, weight, volume and area were not fixed, but increased with sward height ( P < 005). For all sward heights, the horses removed between 51% and 68% of the initial grass length. The horses adjusted their bite dimensions to sward height but did not maximize food intake per bite. The response to sward height might be explained by a preference for easily digested food or the trade-off between energy intake and the cost for food processing.
This experiment suggests that grass height has a major influence on bite dimensions of horses. However there may be more complex factors influencing ingestive behaviour of horses (e.g. age, dietary experience and social behaviour) that have to be considered when horses are grazing pasture.
This study tested the hypothesis that different sward structures, which were constructed by varying the
pre- and post-grazing sward heights of annual ryegrass pasture (Lolium multiflorum Lam.) in southern Brazil, affect the short-term intake rate (STIR) by dairy cows. Treatments consisted of four sward-management strategies defined by a combination of two pre- (25 and 15 cm) and two post-grazing sward heights (10 and 5 cm): 15-05, 15-10, 25-05 and 25-10. A completely randomized block design with four replicates was used for the experimental design. The STIR was determined by the double-weighing technique. Jaw movements were evaluated using automatic recorders (IGER Behaviour Recorder). The results showed that treatment 25-10 allowed the animals to collect more herbage with a greater bite mass and thus resulted in a greater STIR. Treatments in which sward height was reduced to 10 cm generally favoured the ingestion process than treatments with a post-grazing sward height of 5 cm.
This study tested the hypothesis that different sward structures, which were constructed by varying the pre‐ and post‐grazing sward heights of annual ryegrass pasture (Lolium multiflorum Lam.) in southern Brazil, affect the short‐term intake rate (STIR) by dairy cows. Treatments consisted of four sward‐management strategies defined by a combination of two pre‐ (25 and 15 cm) and two post‐grazing sward heights (10 and 5 cm): 15‐05, 15‐10, 25‐05 and 25‐10. A completely randomized block design with four replicates was used for the experimental design. The STIR was determined by the double‐weighing technique. Jaw movements were evaluated using automatic recorders (IGER Behaviour Recorder). The results showed that treatment 25‐10 allowed the animals to collect more herbage with a greater bite mass and thus resulted in a greater STIR. Treatments in which sward height was reduced to 10 cm generally favoured the ingestion process than treatments with a post‐grazing sward height of 5 cm.
The role of a cleft upper lip of alpaca (Lama pacos) in foraging short pastures was investigated using biting forces and associated impulses in animal grazing. Three Merino wethers and three castrated alpacas were used. Ten (10L), 20 (20L), 30 (30L), 40 (40L) or 50 (50L) leaves of orchardgrass (Dactylis glomerata) per load cell were offered to animals, and three-directional biting forces were digitally recorded at 5s−1000. From the total biting force/time curve, grazing impulse was calculated, equivalent to the area surrounded by the curve. The grand mean of the number of grazed leaves per bite was 9.8±0.53 in alpaca and 17.9±1.31 in sheep. Remaining leaf length after grazing trial was significantly lower in alpaca than in sheep (11.9±0.19mm versus 18.5±0.41mm). Alpaca grazed leaves with significantly lower mean biting force (7.0±0.69N versus 20.0±1.80N) and significantly shorter duration time per one biting force (0.11±0.005s versus 0.18±0.19s) than sheep. The grand mean of sum of grazing impulse was lower (P
To maximize herbage DMI, pregrazing sward surface height (SSH) and level of herbage depletion (HD) must be such that variables determining short-term herbage intake such as bite mass (BM) and bite rate (BR) are optimized. The objective of this study was to determine a SSH target and the level of HD as a proportion of the SSH that optimizes BM and BR of beef heifers grazing Sorghum bicolor swards. Two experiments were conducted using 2 S. bicolor swards and 4 beef heifers (25 mo old; 322 kg BW). Experiment 1 compared the effect of 6 pregrazing SSH, 30, 40, 50, 60, 70, and 80 cm, on BM, BR, and jaw movements. Experiment 2 assessed the effect of HD level as a proportion of SSH (0.17, 0.34, 0.50, 0.67 and 0.84) on BM, BR, and jaw movements using the optimal pregrazing SSH defined in Exp. 1. Short-term herbage DMI was estimated using a double-weighing technique and corrected for insensible BW loss. Herbage DMI was subsequently used to calculate the BM. Net eating time and jaw movements for apprehension and manipulation + mastication during grazing as well as total jaw movements were determined using the IGER (Institute of Grassland and Envoronmental Research) behaviour recorders. Bite rate and the number of total jaw movements per gram herbage DMI were derived from jaw movement count and measurements of herbage DMI. The results of Exp. 1 showed low and high SSH constraint the ease of herbage harvesting. Greater BM are maintained until a SSH of 50 cm is reached (P < 0.05) and then decline at greater SSH due to herbage dispersion. The nonbiting jaw movement rate increased at greater SSH whereas BR decreased (P < 0.05). For both variables, the turning point was close to a SSH of 50 cm. Experiment 2 showed that such an optimization of BM and BR was maintained until an HD level of 0.34 was reached (P < 0.05). There was a linear increase in both the total jaw movements per unit herbage DMI and the nonbiting jaw movements rate (manipulation + mastication) subsequent to levels of HD greater than 0.34 (P < 0.05). These studies provide, for the first time, sward feature targets to manage grazing and optimize BM and BR, aiming to maximize the short-term herbage DMI of cattle grazing S. bicolor swards.
Many aspects of the management of grazing systems are directly or indirectly related to the rate of herbage intake achieved by the animal. Intake rate depends, in part, on the time budget of the process, which derives from the basic behavioural component—the jaw movement. Chewing and biting jaw movements have generally been considered mutually exclusive, but acoustic monitoring has demonstrated the existence of the compound chew–bite jaw movement. We used a simple model to examine the implications of chew–bites for the forage-intake time budget, and tested it empirically. The model defines the total number of jaw movements per bite (α) and the number of chew actions per bite (β) in relation to the allocation of jaw movements between chews, bites and chew–bites. We examined empirically the variation among animals in the allocation of jaw movements for cattle (Bos taurus L.) grazing leafy, uniform swards in two separate studies. Grazing sessions were recorded on video, with the sound track originating from a forehead microphone. Each sound burst produced by a jaw movement was classified as a bite, chew or chew–bite. Jaw movements in these segments generated a virtually uninterrupted, regular succession of bite, chew and chew–bite sounds. Among individual animals, the variation in the rate of jaw movement was extremely low (Study 1: mean=78.9min−1, CV=6%; Study 2: mean=77.9min−1, CV=4%), but variation in the allocation of jaw movements was high (CV of proportion of jaw movements allocated to bites, chews and chew–bites=58, 21 and 50%, respectively, for Study 1; 32, 12 and 32%, respectively, for Study 2). The proportions of chews and bites traded off directly against chew-biting. As the proportion of chew–bites increased, the number of jaw movements per bite declined and therefore the bite rate increased. Different combinations of the three types of jaw movement conformed to an isocline of a constant number of chew actions per bite (CV=11 and 9% for Studies 1 and 2, respectively). Furthermore, this ratio was close to unity (1.27 and 1.24 chews per bite for Studies 1 and 2, respectively), and was similar for different levels of herbage mass in the range 145–255gm−2. The possible implications of these findings for the regulation of bite weight and diet quality are discussed.
Grazing by cattle on the scale of a single feeding station was studied to determine the patterns of defoliation and bite dimensions in short bite sequences. The sward was a continuous and homogeneous expanse of alfalfa without any imposed patchiness of structure. Treatments were bite sequences of 3, 6, 9 and 12 bites, with the forelegs of the observed animal stationary. Four 18-month-old heifers were used and the treatments were conducted over two grazing cycles. The bite scale defoliation imprints (non-contiguous grazed areas separated by undefoliated vegetation) were marked with white spray paint and photographed for shape and area measurements.
The effect of sward bulk density on bite mass and bite dimensions was examined in two experiments using oesphageally fisulated cows to graze microswards under field conditions. In Experiment 1 microswards of uniform sward height were hand thinned to create differences in sward bulk density. In Experiment 2 plots were sown with monocultures of a range of ryegrass cultivars selected on the basis of their contrasting sward structures to provide a range of sward bulk densities and grazed down in two consecutive strata. Both methods were successful in providing a range of microswards of different sward bulk densities. In Experiment 1 bite mass increased significantly as sward bulk density increased. In Experiment 2 bites taken from the first stratum did not differ significantly in mass due to bites being deeper in swards with low bulk density, compensating for the lower bite bulk density. However, mass of bites taken mainly from the second stratum were lower in some swards due to lower bite bulk density which was related to tiller density rather than sward bulk density. The results emphasize the importance of sward bulk density in determining bite mass and dimensions, especially for the first stratum, and of tiller density in the bulk density of bites in the lower stratum in sward depletion, the latter requiring to be studied further.
A better understanding of the animal x plant interaction is needed to develop management practices which will maintain a sufficiently rich and abundant vegetation in the pastures. Such practices would permit the animals to meet their nutritional requirements, and to ensure a sufficient production, while contributing to the maintenance of the environment. This review, drawn on a large number of experimental studies, takes stock of the factors influencing the selection and use of feeding sites and stations by herbivores. First, we present the theoretical framework in which the experimental observations are discussed. The general context of optimal foraging theory (OFT) and its predictions are described. Its 'applicability', usefulness and validity to study the foraging behaviour of herbivores are then discussed. Second, we analyse how forage (quantity and quality, plant species, distribution), environment (topography, distance to water, predator risk) and some animal factors (cognitive abilities, social organisation) affect the choice and use of feeding sites and stations. In spite of some problems of definitions ('patch', 'prey' for an herbivore?) and of the herbivores' specific characteristics, the OFT has been successfully used to explain the foraging behaviour of herbivores. However, animals' choices are rarely as absolute as predicted. Under natural conditions, animals not only respond to food resource, but are also constrained by some non-alimentary environmental factors and by the limits of their cognitive abilities (memory, discrimination). Other complementary approaches, such as 'hedonism' and 'nutritional wisdom', can partly influence animals' choices and are also briefly discussed. ((C) Elsevier/Inra).
Grazing by domesticated herbivores is discussed as a process of depletion in which the removal of herbage may be associated with a change in intake rate over a defined time period by virtue of changing options for bite selection. A model of depletion is presented in which a non-growing, non-patchy sward of finite area is described as a series of grazing horizons. Each horizon provides a number of potential bites equal to the ratio between horizon area and the bite area characteristic of the horizon. Bite weight is constant within horizon but may differ between horizons. Where depletion influences instantaneous intake rate, a model that describes the sward as a set of characteristic bites differentiated into horizons is more appropriate with greater emphasis on sward biomass. A bite-oriented approach with greater emphasis on sward structure may be necessary to understand the considerable variation in functional response to herbage allowance obtained in studies of high depletion systems. -from Authors
Patch depression is an essential premise of optimal patch use models. We studied the relationship between patch residence time and intake by Bos taurus. The hypotheses were: (1) grazing changes sward structure and thus, causes patch depression; (2) patches are grazed systematically, by horizon; (3) at equal herbage mass per unit area, tall and sparse swards yield larger bites and thus, exhibit faster and greater depletion than short dense ones. In one experiment, we constructed 0.46-m^2 swards of wheat (Triticum aestivum L.) with two contrasting structures but equal herbage mass. In a second experiment we mowed a perennial ryegrass (Lolium perenne L.) field to produce 0.36-m^2 patches of three heights (7, 12.5, and 18 cm). The animals were allowed to remove different numbers of bites from each patch type, and we measured bite mass, intake, and residence time. Bite dimensions and location (fresh or gazed area) were also recorded in the first experiment. In the first experiment, bite mass was initially larger and decreased more steeply with residence time in the tall sparse swards than in short dense ones. Because bite dimensions and mass declined but time per bite did not change, instantaneous intake rate declined as patches were grazed. Animals grazed systematically and removed most of the top half of the canopy before biting into the lower horizon. A rectangular hyperbola described intake curves (cumulative intake vs. time) well but ignored the abrupt change in instantaneous intake rate when the top horizon was depleted. A model based on the horizon grazing style accurately depicted this change in slope but disregarded the reduction in bite mass within horizons. Intake curves for the field patches were more variable than for hand-constructed patches, but were well described by a rectangular hyperbola. Taller patches had more herbage mass and allowed greater bite mass than shorter ones. Therefore, intake curves had initially steeper slopes and approached higher asymptotes than in shorter patches. Grazers experienced patch depression at the scale of feeding stations. Plant height and density are the causal factors of this process.
The objectives of this study were to contribute to the understanding and quantification of the effect of sward structure on the ingestive behavior and intake of livestock. Hand-constructed swards of approximately 0.43 m² were used to determine the bite dimensions, bite weight, and short-term intake rate of steers (Bos taurus L.) grazing short swards. Swards were constructed of leaf blades of Paspalum dilatatum Poir. at homogeneous heights of 0.04, 0.06, 0.08, and 0.10 m and heterogeneous heights with means of 0.06 and 0.10 m at two leaf densities. Treatments were replicated using three 4-yr-old steers. Bite depth (B) was defined as the initial sward height (H) minus the mean residual height of grazed leaves. Bite area (A) was defined as the surface area represented by the mean number of leaves grazed per bite. Leaf density had no effect on bite dimensions. Linear regression of B on H and linear regression of A on H explained 99% and 89% of the variance, respectively. Mean bite weight ranged from 0.053 to 0.807 g. Correlation of measured bite weight with the product of the measured B, A, and bulk density yielded a coefficient of determination of 0.97. Mean intake rate ranged from 131 to 1473 g h⁻¹. Bite weight accounted for 93% of the variance of intake rate. Bite dimensions on heterogeneous swards were similar to those on homogeneous swards, though by different mechanisms. The importance of biting overlap, leaf insertion in the mouth, and tongue sweeping are discussed in relation to mean bite dimensions and weight.
Contribution no. 3123-E, 1990 series, from the ARO, Bet Dagan, Israel. Research supported by the United States-Israel Binational Agric. Res. and Dev. Fund (BARD), Project no. US-1329-87
Please view the pdf by using the Full Text (PDF) link under 'View' to the left. Copyright © . .
Numerous experiments have shown that animals grazing pasture remove only a portion of the sward height offered. Furthermore, bite area increases with sward height but decreases slightly as sward bulk density increases. A number of theories have been proposed to explain these patterns. One suggestion is that bite depth is limited by barrier layers of mature pseudostem or reproductive stem in the canopy. Animals may then adjust their bite area to maintain a constant bite fracture force. However, recent studies show that these hypotheses are unlikely to be true except in limited circumstances. This paper develops a theory of bite mechanics to describe and explain the bite dimensions of sheep and cattle grazing grass swards in terms of physical processes. Bite mechanics are described using simple mathematical functions that assume a non-constant bulk density profile and a non-cylindrical bite volume. Bite `depth' (insertion height) is assumed to be proportional to sward surface height. Bite area responses can then be explained by the extent to which this non-cylindrical bite volume is inserted into the canopy and by the observation that animals decrease potential bite area slightly in response to increasing pasture bulk density. Bite area and bite weight calculations derived from these models are consistent with published data from sheep and cattle grazing artificial swards. Areas for further experimentation are suggested.
To identify and quantify the influence of sward structure on the intake of grazing animals requires an understanding of sward-animal interactions at the bite level. We tested the hypothesis that bite dimensions on vertically heterogeneous swards are determined by structural characteristics of the top leaf stratum, independent of those of a bottom layer of pseudostem or stem. Dallisgrass (Paspalum dilatatum Poir.) microswards were constructed by hand in a factorial combination of two lamina lengths (5 and 8 cm) and two sward heights and 16 cm). Tillers consisted of a top segment of lamina and a bottom one of pseudostem (Exp. 1) or stem (Exp. 2) of length equal to difference between sward height and lamina length. Treatments were replicated over three steers (Bos taurus) of 750 kg avg. body weight. Bite area and depth increased with sward height in swards with pseudostem but were not affected by lamina length. Pseudostems were not a barrier to defoliation and did not affect bite dimensions. Steers restricted grazing of tillers with stem to the upper lamina horizon. Bite depth was limited by stems only when lamina length was less than half of sward height. Bite area was reduced by the presence of stems because tillers bent at ligule height, restricting the animals to gather fewer tillers in each bite than when tillers bent at the base. Bite weight was reduced severely in swards with stem, relative to those with pseudostem. Results confirmed the importance of stem horizons and their relative positions in the sward as determinants of bite weight.
Research supported by BARD Grant no. US-1329-87.
Please view the pdf by using the Full Text (PDF) link under 'View' to the left. Copyright © . .
Grazing trials were conducted on high elevation summer range where sheep were stocked alone and in common with cattle in .4-ha paddocks to explore the use of grazing behavior as an indicator of forage availability. Sheep behavior was monitored by recording the length of time that individual ewes spent at a feeding station, defined here as feeding station interval. As grazing progressed, sheep increased the number of feeding station intervals that were less than 10 s long. That trend, decreased grazing time at each station, was consistent regardless of whether sheep grazed alone or with cattle. When sheep grazed with cattle, however, time spent at each feeding station was longer, further into the grazing trials. At high stocking densities, livestock feeding behavior seemed to change rapidly in response to declines in forage availability. Sensitive indicators of these changes are apparent in animal behavior with close scrutiny of animal movements. Monitoring animal behavior during feeding periods might allow the manager to recognize nutritional limitations in the available forage and perhaps adjust management strategies accordingly.
Five grazing trials using Suffolk wethers were carried out at Obihiro, Japan from June to July of 1989 and 1990. New methodology was developed to investigate bite weight and bite selection using hand-constructed swards, which were composed of 128 points of plant units spaced 4 cm apart. Leaves and reproductive culms of orchardgrass ( Dactylis glomerata ) and timothy ( Phleum pratense ) were used in five kinds of artificial swards (three pure leaf mixtures and two leaf/culm mixtures).
In the leaf/culm mixture, sheep definitely selected leaf units. The inclusion of reproductive culms decreased the number of prehending bites and the total distance of travel between bites. Mean distance of travel between bites was 8·6–10·6 cm. Mean travelling speed was 7·2 cm/s and was not influenced by the inclusion of culms. Total distance of travel between bites was 3·8–4·1 m/min in pure leaf mixtures and 3·4–3·5 m/min in leaf/culm mixtures.
The actual area covered by one prehending bite, estimated from direct measurement, was 21–27 cm ² in pure leaf mixtures and 15–16 cm ² in leaf/culm mixtures. Decreased bite area in leaf/culm mixtures resulted in decreased bite weight and intake rate. Experimental errors observed were discussed with respect to the biting behaviour of sheep and flexibility of grass leaves.
Effects of sward height and density on the dimensions and weights of bites taken by cattle were examined. In one experiment, swards of dallisgrass lamina were constructed by hand in a factorial combination of four heights (80, 150, 180 and 300 mm) and three densities (c. 700, 1500 and 2700 g m−3). In the other, swards of lucerne were constructed in a factorial combination of three heights (70, 150 and 250 mm) and three densities (1500, 2800 and 5900 g m−3). Treatments were replicated on three steers of 750 kg average weight. The first six bites taken from the sward were monitored, and functional relationships between sward characteristics and bite dimensions derived. Results from both experiments were similar. Average bite area was not constant as often assumed, but decreased linearly with density and increased quadratically with height, with slope negatively affected by density and height. In tail swards, bite area reached a plateau of c. 170 cm2, determined by the sweep of the tongue. In contrast with the widely used model, bite depth increased linearly with height, with slope negatively affected by density. Response of bite dimensions was explained by the mechanics of the interaction between tongue and jaw movements, and sward structure. Bite weight varied less than bite dimensions, because of compensatory effects between bite area, bite depth and density. Animals obtained heavier bites in tall sparse swards than on short dense ones of equal mass/area. Even in homogeneous swards, both density and height are necessary to predict bite weight.
A simple model of depletion by a grazing ruminant was tested at high depletion levels and for different sizes of feeding station. The model divides an initially uniform sward profile into grazing horizons, dependent on bite depth, and assumes a constant within-horizon bite area.
Two grazing experiments were conducted using cattle. Uniform areas of oats and alfalfa herbage were grazed individually to a high level of depletion (≈150 bites m–2). Feeding station areas were 0·16, 0·30 and 0·53 m2. Initial sward heights were 10 and 20 cm in oats and 20 cm in alfalfa. Size of area did not significantly affect the observed number of bites removed per square metre, the mean residual herbage height or mass, or the proportion of each grazing horizon depleted, derived from the frequency distribution of residual heights. The mean residual height for all treatment combinations could be explained by assuming a ‘take half’ rule for mean bite depth, and allowing for the derived proportion of the area of each grazing horizon depleted.
A simple bite placement simulator was used to generate, for a single grazing horizon and for a given maximum potential area of a bite, the expected relationship among mean effective area of a bite, the proportion of the area of the horizon grazed and the number of bites removed per unit area. The simulator mimics a loosely systematic grazing style. The observed bite numbers and the derived proportions of grazing horizon depleted can be reconciled if the within-horizon mean effective bite area is not constant but declines as predicted by the bite placement simulator. The implications for the shape of the gain function within a feeding station are discussed.
A test apparatus was developed to study feeding station (FS) use and abandonment by sheep, by controlling FS number, characteristics and distance between FS. It consists of a rectangular pen with openings in one of the long sides through which the animal can extend its head to graze. The aims of this experiment were (i) to study FS behaviour of ewes according to the number of FS offered, at two sward heights, and so (ii) to determine the test conditions (FS number, test duration, sward height) most conducive to grazing. Eight dry ewes were offered four grazing treatments (two FS numbers (8 vs. 12) × two sward heights (7 vs. 15 cm)), during four 3-day periods. The ewes were fasted for 17 h and then tested individually for 15 min. A 34-session preliminary training period was necessary to select suitable animals. Behaviour at FS was independent of the FS number, until min 10, when idling increased, particularly for 8 FS and on short sward. A test limited to 10 minutes using an 8-station device seems practical, subject to a sufficiently motivating sward height. FS behaviour was closely related to sward height: grazing time per FS was longer on tall than short swards, which was consistent with field observations and optimal foraging predictions. However, grazing times per FS were much longer in test than in field conditions, which may partly be explained by the absence of fellow animals, a long fast, and constraints of the device.
A conceptual model to explain variation in ingestive behaviour within a feeding patch Proceedings XVII International Grassland Congress
- E A Laca
- M W Demment
- R A Distel
- T C Griggs
Field test of optimal foraging with cattle: the marginal value theorem successfully predicts patch selection and utilisation Proceedings XVII International Grassland Congress
- E A Laca
- R A Distel
- T C Griggs
Ingestive behaviour The Ecology and Management of Grazing Systems
- E D Ungar
JMP User’s Guide Version 3. Cary NC: SAS Institute
- Sas Institute
The Ecology and Management of Grazing Systems
- D Ungare