M.J. Auldist’s research while affiliated with University of Melbourne and other places

Dry matter intake (DMI) is a primary determinant of milk production in grazing dairy cows and an ability to measure the DMI of individual cows would allow herd managers to formulate supplementary rations that consider the amount of nutrients ingested from grass. The 2 related aims of this experiment were to define the mean number of swallowed boli and mass of the swallowed boli in Holstein-Friesian dairy cattle offered a variety of forages commonly fed in the dairy industry of southeastern Australia, and to evaluate 2 indirect methods for counting the number of swallows. Twelve ruminally-fistulated, lactating Holstein-Friesian cows were randomly assigned to 3 replicated 4 × 4 Latin square designs and offered 4 forages: fresh chicory (FC), fresh perennial ryegrass (RP), alfalfa hay (AH), and perennial ryegrass silage (RS). The experiment was conducted over 28 d with each of 4 periods consisting of 7 d with 3 d of measurement. Forage diets were offered to individual cows following the partial evacuation of the rumen. The first 20 min after forage was offered constituted the measurement period, during which all swallowed boli were manually captured by samplers who placed their hand through the ruminal fistula and over the cardia entrance of the rumen of each cow. Concurrently, microphones and video cameras were used for the indirect measurement of swallows. The average swallowed bolus mass overall was 17.4 g dry matter (DM) per bolus with the lowest mass observed in cows offered FC (8.9 g DM/bolus), followed by RP (14.9 g DM/bolus), compared with cows offered AH (23.6 g DM/bolus) and RS (22.3 g DM/bolus). The swallowing rate was greater in cows offered FC (78 swallows/20 min) than in cows offered RP, AH, and RS (62.3 swallows/20 min). The audio recording method showed greater concordance (Lin's concordance correlation coefficient = 0.90) with the physical capturing of the boli through the rumen, than the video recording method did (Lin's concordance correlation coefficient = 0.54). It is concluded that the mass of the swallowed boli is related to forage type and that using a microphone attached to the cow's forehead can provide an accurate measure of the number of swallows when verified against the actual number of swallows counted by manual interception of the boli at the rumen cardia.

Bite mass is the dry matter ingested per prehension bite. It has previously been reported that sward characteristics such as herbage height, density and allowance can affect bite mass in grazing cows. Animal characteristics such as liveweight and incisor arcade breadth may also affect bite mass. Understanding factors that influence bite mass can lead to an improvement in the estimate of dry matter intake of grazed herbage. The aim of this study was to determine the effects of liveweight and incisor arcade breadth on average daily bite mass of grazing dairy cows. The research consisted of two parts. In Part I, 113 multiparous lactating Holstein-Friesian cows were assessed for their 7-d average liveweight and incisor arcade breadth. In Part II, from the 113 cows screened in Part I, 32 cows were selected for use in a grazing experiment. The 32 cows were allocated to one of four groups of 8 cows based on the following factors: light cows (mean liveweight of 542 kg) with narrow incisor arcade (mean of 8.2 cm) (LN), light cows (mean liveweight of 581 kg) with wide incisor arcade (mean of 9.5 cm) (LW), heavy cows (mean liveweight of 658 kg) with narrow incisor arcade (mean of 8.2 cm) (HN) and heavy cows (mean liveweight of 660 kg) with wide incisor arcade (mean of 9.5 cm) (HW). Each cow grazed in an individual plot and herbage intake was calculated as the difference between estimated pre-and post-grazing herbage mass in each plot, as measured with a rising plate meter. Prehension bites were counted using jaw movement sensors. In Part I, incisor arcade breadth of the cows was between 7.0 and 9.8 cm and liveweight was between 490 and 745 kg. There was no relationship (P = 0.30) between liveweight and incisor arcade breadth of these cows. In Part II, mean bite masses were 0.46, 0.50, 0.50 and 0.49 g DM/bite for LN, LW, HN and HW, respectively and the differences between them were not significant (P = 0.30, SED = 0.03). There was also no effect of liveweight category (P ≥ 0.68) or incisor arcade breadth category (P ≥ 0.72) or their interaction (P ≥ 0.78) on prehension bites, mastication chews or total eating bites. These findings suggest that mechanistic models for estimating bite mass and herbage intake may not need to include liveweight or incisor arcade breadth.

To increase the dry matter and metabolisable energy intake of cows, dairy farmers often supplement pasture with concentrates and conserved fodder. Feeding large amounts of highly fermentable concentrates to cows can result in metabolic issues, such as ruminal acidosis, and thus safer but more efficient introduction strategies are desirable. We assessed the role that forages play in ruminal, behavioural and production responses to a wheat grain challenge in dairy cows with no previous wheat adaptation. Multiparous lactating Holstein dairy cows (n = 16) were fed a forage-only diet of either lucerne (Medicago sativa) hay, perennial ryegrass (Lolium perenne L.) hay or one of two cultivars of zero-grazing fresh perennial ryegrass herbage (Bealey or Base), for 3 weeks. The forage diet was then supplemented with crushed wheat grain at 8 kg dry matter/cow day−1, with no adaptation period. Wheat comprised between 32 and 43% of total dry matter intake. Cows fed hay maintained a higher mean ruminal fluid pH than those fed herbage, on both the forage-only diet (6.43 vs. 6.17) and the forage plus wheat diet (6.03 vs. 5.58). Following supplementation of wheat, cows fed herbage exhibited minimum ruminal fluid pH levels indicative of acute ruminal acidosis, at 5.15 and 5.06 for cultivars Bealey and Base, respectively. Furthermore, for both herbage cultivars, adding wheat resulted in a ruminal fluid pH under 6 for >20 h/day. The ruminal environment of cows fed lucerne hay remained most stable throughout the grain challenge, spending the least amount of time below pH 6.0 (9.0 h/day). Hay created a ruminal environment that was better able to cope with the accumulation of acid as wheat was digested. A combination of increased ruminating time and a slower rate of fermentation, due to higher neutral detergent fiber and lower metabolisable energy concentrations in the hays, is likely responsible for the higher ruminal fluid pH values. Forage plays a critical role in wheat introduction strategies; aggressive adaptation strategies could be implemented when a hay such as lucerne is used as the base forage.

The RumiWatch System (Itin+Hoch GmbH, Liestal, Switzerland) is a sensor system that enables quantification of ingestive behaviors of cattle that may be useful, amongst other things, for estimating dry matter intake. There are currently multiple versions of the RumiWatch Converter software used to convert the recorded data into specific animal behaviors through the use of algorithms. The objective of this research was to evaluate the use of RumiWatch System noseband sensors for quantifying the number of prehension bites and mastication chews in grazing and stall-fed dairy cows using RumiWatch Converter software versions 0.7.3.36 (RWC36) and 0.7.4.13 (RWC13). Two experiments using lactating Holstein-Friesian dairy cattle were conducted. In Experiment I, ten cows grazed perennial ryegrass pasture (Lolium perenne L.) in individual plots that measured 35 m², with a pasture mass of 2,500 kg DM/ha and pasture allowance of 28 kg DM/d. In Experiment II, 14 cows were offered 16 kg DM/d of perennial ryegrass pasture silage in individual indoor feed stalls. In both experiments, ingestive behaviors were quantified with the jaw movement halters and through visual observation using video recordings. The performance of the RumiWatch Converter software was evaluated through Lin’s concordance correlation coefficients with video observation. For grazing cows, there was greater concordance between the RumiWatch System and video observation for the number of prehension bites (0.94 for RWC36 and 0.75 for RWC13) than for the number of mastication chews (0.20 for RWC36 and 0.14 for RWC13). In cows fed in stalls, there was also greater concordance for the number of prehension bites (0.54 for RWC36 and 0.64 for RWC13) than for the number of mastication chews (0.46 for RWC36 and 0.58 for RWC13). However, the RWC36 was more accurate for quantifying feeding behaviors of grazing cows than the RWC13, while for stall fed cows the reverse was true. Overall, both RumiWatch Converters were better at quantifying prehension bites in grazing cows than in stall fed cows, but better at quantifying mastication chews in stall fed cows than grazing cows. These data enable a new understanding of the how these RumiWatch sensors should best be used for measuring cows' feeding behaviors in different feeding systems.

The economics of grazing dairy cows offered a range of herbage allowances and fed supplements as a partial mixed ration (PMR) were examined where profit was defined as the margin between total milk income and the cost of pasture plus PMR supplement. The analysis made use of milk production and feed intake data from two dairy cow nutrition experiments, one in early lactation and the other in late lactation. In early lactation and at a PMR intake of 6 kg DM/cow per day, the profit from the cows with access to a medium herbage allowance (25 kg DM/cow per day) was AUD 1.40/cow per day higher than that for cows on a low allowance (15 kg DM/cow per day). At a higher PMR intake of 14 kg DM/cow per day, the profit from the cows on a medium herbage allowance was AUD 0.45/cow per day higher than the cows on a low allowance; there was no additional profit from increasing the herbage allowance from medium to high (40 kg DM/cow per day). In late lactation, the profit from the cows fed a PMR with a medium herbage allowance (20 kg DM/cow per day) was only higher than the cows on a low allowance (12 kg DM/cow per day) when the PMR intake was between 6 and 12 kg DM/cow per day. There was also a difference of AUD +0.50/cow per day between the PMR with medium and high herbage allowance (32 kg DM/cow per day). It was concluded that farmers who feed a PMR to dairy cows should offer at least a medium herbage allowance to optimize profit. While feeding additional PMR increases milk production and profit, further gains would be available by offering a higher herbage allowance. These findings provide an estimate of the net benefits of different herbage allowances when feeding a PMR and will enable farmers to manage their feeding systems more profitably.

Dry matter intake (DMI) of herbage is a product of bite rate and bite mass and is a determinant of the performance of grazing ruminants. This research tested the effect of herbage allowance and herbage mass on average bite mass of individual dairy cows grazing perennial ryegrass herbage (Lolium perenne L.). Two experiments were conducted, one in each of winter (Experiment 1) and spring (Experiment 2). In each experiment, 24 Holstein-Friesian dairy cows grazed individual perennial ryegrass plots over 10 d. In each experiment cows grazed one of six treatments: low or medium herbage mass (1,900 or 2,200 kg DM.ha⁻¹ in Experiment 1 and 2,200 or 3,000 kg DM.ha⁻¹ in Experiment 2) combined with either low, medium or high herbage allowance (15, 25 or 40 kg DM.cow⁻¹.d⁻¹ in Experiment 1 and 20, 30 or 40 kg DM.cow⁻¹.d⁻¹ in Experiment 2). Grazing behaviour was measured with jaw movement sensors and DMI was determined by herbage disappearance measured with a rising plate meter daily, and at hourly intervals during the first 4 h of grazing after the morning milking. Average bite mass (g DM.bite⁻¹) per day and per hour was determined as the mass of herbage that had disappeared in each period (g.d⁻¹ or g. h⁻¹) divided by number of prehension bites in that period. The combined data from two experiments was analysed by Linear Mixed Model and it was found there was no effect of herbage mass (P = 0.686) on bite mass per day. However, cows offered high herbage allowance had greater (P < 0.001) bite mass per day (0.62 g DM.bite⁻¹) than cows offered the lowest herbage allowance (0.38 g DM.bite⁻¹) across both experiments. The effect of herbage allowance was similar across both herbage masses. Bite mass per hour was the highest (P < 0.001) in the first hour of grazing in both experiments with average bite mass per hour across two experiments in the first hour of grazing (0.69 g DM.bite⁻¹) greater than in the second (0.40 g DM.bite⁻¹), third (0.35 g DM.bite⁻¹) and fourth (0.32 g DM.bite⁻¹) hours of grazing. We conclude that herbage allowance is a significant factor in determining bite mass and should be included in models aimed at predicting bite mass and hence daily herbage intake of grazing dairy cows.

Accurate measurement of pasture depletion and, therefore, dry matter intake (DMI) is fundamental in both research and commercial settings for understanding the behaviour and nutrition of grazing animals. Remote sensing technologies such as unmanned aerial vehicles (UAV) equipped with sensors have been used to estimate biomass of crops and un-grazed pastures. The aim of the experiment reported here was to develop and validate empirical models to estimate pasture depletion in paddocks while cattle are grazing using an UAV-borne multispectral sensor with a rising plate meter measurements as the reference data. Data were collected in winter and spring with 24 different cows used in each period and grazing in individual plots. UAV flights were undertaken before cows entered the paddock and then every hour for the first 5 h of grazing coinciding with rising plate meter measurements. Four types of datasets were prepared and compared to determine which produced the best estimate of herbage mass. The first two datasets were created by extracting data from either the cow’s whole AM plot (AP) area, or a small polygon of homogenous data (SP) subjectively chosen from within the AM plot area. A further two training datasets were created by combining either the AM plot data or small polygon data with additional extreme data (EX) collected pre (0 h) and post (24 h) grazing from days before or after the days of UAV measurements. Therefore, the four training datasets compared were AP, SP, APEX and SPEX. The best performing model was the APEX model with a concordance correlation coefficient of 0.67, an r² of 0.54 and RSME of 406 kg DM/ha in independent validation, however accuracy of estimates decreased with pasture biomass below 1,000 kg DM/ha and above 2,000 kg DM/ha. Dry matter intake estimated using the UAV images and the APEX model had a concordance of 0.39 with the RPM method. The APEX model was also used to demonstrate how this model allowed pasture depletion to be mapped through time during a grazing session. This research has highlighted the potential of using a UAV-borne multispectral imaging system for estimating pasture depletion in paddocks while cows graze, however, we suggest further research is required to improve the accuracy of our models for estimating extreme values of pasture biomass before it can be used to estimate daily DMI.