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Assessment of diet composition of free-ranging antelopes (Addax nasomaculatus) by the combination of microhistological procedures and n-alkanes and long-chain alcohols as faecal markers
Abstract
Understanding herbivore foraging behaviour is crucial for adequate wildlife management decisions. This study assessed the diet composition of free-ranging addax antelope (Addax nasomaculatus (de Blainville, 1816)). Samples collected during the spring season were analyzed using microhistological procedures along with n-alkanes and long-chain alcohols as fecal markers. Twelve animals were monitored and fresh fecal samples were collected daily during a 7-day period. Diet composition estimates obtained by both methods were similar and indicate that Stipagrostis pungens (Desf.) De Winter was the main diet component followed by Fagonia glutinosa Delile, Helianthemum kahiricum Delile, and Hammada schmittiana (Pomel.) Botsch. Data showed that addax have mixed diets composed of perennial woody and herbaceous plant species depending on their availability. The four species most selected by the animals were also the most abundant species in terms of plant cover. In contrast, species that accounted for less than 5% of the plant cover were not present in the fecal samples. Results of this study represent a single grazing season, and for that reason, further studies are required to fully understand how the grazing behaviour of addax varies with seasonal changes in vegetation cover.
... Campos-Arceiz et al., 2004; (5) Clemente et al., 2009; (6) Codron et al., 2007; (7) Cook, 2002; (8) Dagg, 2014; (9) Davis et al., 2008; (10) Djagoun et al., 2013; (11) Flores-Miyamoto et al., 2005; (12) Gagnon and Chew, 2000; (13) Hart and Hart, 1989);(14)Heffelfinger, 2018; (15) Hejcmanová et al., 2010; (16) Hofmann and Roth, 2003; (17) Jiang et al., 2002; (18) Johnsingh and Sankar, 1991; (19) Leslie, 2008; (20) Marin et al., 2020; (21) Müller et al., 2011; (22) O'shaughnessy et al., 2014; (23) Owen-Smith, 1997; (24)Pinder and Grosse, 1991; (25) Renecker and Schwartz, 1997; (26) Schaller, 1967; (27) Sempéré et al., 1996; (28) Seri et al., 2018; (29) Sokolov, 1974; (30) Tomas and Salis, 2000; (31) Tripathi et al., 2019; (32) Tuboi and Hussain, 2016; (33) Wegge et al., 2006; (34) Wilson and Mittermeier, 2011; (35) Watter et al., 2020. ...
Knowledge on diet selection of different herbivore species under each specific vegetation community is essential to develop and apply appropriate management decisions for each grazing system in order to, simultaneously, have a more efficient and sustainable utilization of pasture resources and the best animal performance level. In this chapter, traditional and more recent methodologies that can be used for studying diet selection of both domestic and wild herbivores are briefly presented, identifying the main advantages and limitations of their use. Particular emphasis is given to the utilization of epicuticular compounds, namely alkanes, long-chain fatty acids and long-chain alcohols, as faecal markers. The validation of their use is presented taking into account studies performed with different animal species under controlled conditions. The main advantages and shortcomings for their application to field studies with grazing animals are highlighted. Data indicate that the combination of these epicuticular compounds seems promising to overcome the enumerated constraints, allowing its application to more complex vegetation communities.
This study was carried out in the region of Ouled Chehida located in the Tunisian south. It aims at assessing the impact of the exploitation (grazing) on the dynamic of plant cover of various types of rangelands of the region. The variations of the cover rate, the species density, specific diversity as well as the grazing value both in grazed and rested rangelands were observed. The results of this study show that all observed parameters vary enormously from one rangeland type to another according to the degree of disturbance and that the practice of the rest technique seems to be very beneficial for the whole of parameters and this in spite of the high soil and climatic aridity.
L'étude de la composition chimique de principales plantes broutées par le dromadaire à savoir Calligonum cosmosum, Cyperus conglomeratus, Danthonia fragilis, Gymnocarpos decander, Panicum turgidum, Pithoranthus chloranthus, Retama retam, Stipagrostis pungens, Tamarix gallica et Traganum nudatum, récoltées dans les différents parcours camelins du Sahara occidental algérien , laisse apparaitre une grande variabilité interspécifique. La valeur en matière azotée totale la plus élevée est enregistrée chez le Rtam (Retama retam). Cette espèce est abondante au niveau des parcours sablonneux. Elle est réputée toxique pour les ovins et les caprins, bien qu'elle est broutée par le dromadaire dans certaines conditions. En revanche, la valeur la plus basse est enregistrée chez Panicum turgidum, espèce abondante dans les lits d'oueds à Acacia radiana. Par ailleurs, les plantes les plus appréciées ont des valeurs élevées en cellulose brute et faibles en matière azotée totale. En effet, le comportement alimentaire et le choix des plantes nourricières par le dromadaire sont en fonction de la composition chimique de l'aliment, du stade phénologique de la plante, de la saison et de la composition floristique des parcours. Chemical composition variability of main grazed plants by the dromedary in the Southwestern of Algeria Summary The study of the chemical composition of the main plants grazed by dromedary namely Calligonum cosmosum, Cyperus conglomeratus, Danthonia fragilis, Gymnocarpos decander, Panicum turgidum, Pithoranthus chloranthus, Retama retama, Stipagrostis pungens, Tamarix gallica and Traganum nudatum, collected within different rangelands of the AlgerianWestern Sahara, shows a high variability among the different species. The highest total nitrogenous matter value was recorded in the Rtam (Retama retama). This species is abundant in sandy pastures. It is reputed to be poisonous to sheep and caprine races, though it is grazed by dromedary in certain conditions. On the contrary, the lowest value was recorded in Panicum turgidum, abundant species in Acacia radiana wadis. However, the most appreciated plants present high values in crude cellulose and low ones in total nitrogen. Indeed, the food mode and the selection of nourishing plants by the dromedary are based on food chemical composition, the phenological stage of the plant, the season and the floristic composition of rangelands.
An Aristida pungens-Retama retam rangeland in the arid Jeffara plain in Libya produced 2,000 and 950 kg (dry matter) ha-1 of net above-ground phytomass with 200 mm and 171 mm of rainfall during the 1977/78 and 78/79 growing seasons, respectively. Annual plants contributed 460 and 300 kg (dry matter ha-1) in the 2 seasons, respectively. Perennial shrubs lost their 1978 winter-spring aerial production during the long 1978 summer and dry winter when grazable forage was most needed. In contrast, spring production of annual plants remained available and grazable until late summer. Settlement of shepherds' families on site is not advised as the dead standing phytomass (270 kg dry wood ha-1) may be rapidly exhausted for fuel consumption, leading to wind erosion problems on presently fixed sand dunes.
Knowledge about forage is fundamental to the survival of pastoral populations around the world. In this paper, we address the knowledge of camel forage of Sahrawi nomads and refugees of Western Sahara. We analyze the distribution of this knowledge through cultural consensus analysis and develop an explanation for intra-cultural variation based on changing processes of knowledge transmission. In total, 100 plant species were free-listed by informants, with five species (i.e., Acacia tortilis (Forssk.) Hayne, Nucularia perrinii Batt., Astragalus vogelii (Webb) Bornm., Panicum turgidum Forssk., and Stipagrostis plumosa Munro ex T.Anderson) found to be culturally highly salient. These five represent five local categories of forage that are necessary for camel management in the Western Sahara desert. The Sahrawi listed 25 forage plants that influence the taste and properties of camel milk, demonstrating that cultural values, as much as survival functions, underpin local knowledge systems. Perhaps unsurprisingly, age and nomadic experience are positively correlated with forage knowledge. Forced displacement and sedentarization are hypothesized as causes of progressive non-use of this knowledge and the lack of its transmission to younger generations of refugees. Nonetheless, across the study area, refugees are re-engaging with pastoralism and nomadism, which is leading to a revitalization of forage knowledge and its transmission. This should be regarded as an adaptation pathway for refugees.
As an important constituent of animal feeds, fiber represents the portion of feeds that is bulky and difficult to digest. The neutral detergent fiber (NDF) method, developed over 30 years ago, is the method of choice for measuring total fiber in for-ages and other feeds. Several modifications that were made to improve its general applicability to all feeds and others developed in individual labora-tories often resulted in variability among laborato-ries in measuring NDF. The amylase-treated NDF (aNDF) method, therefore, was developed as an ac-curate and precise method of measuring total in-soluble fiber in feeds. A collaborative study was conducted to evaluate the repeatability and reproducibility of the aNDF method over the full range of animal feed materials. Twelve laboratories representing research, feed company, regulatory, and commercial feed testing laboratories analyzed 11 materials as blind duplicates. The materials rep-resented feed matrixes, including animal products; high-protein, high-fat, and high-pectin feeds; oil seeds; grains; heated by-product feeds; and le-gume and grass hays and silages. Materials se-lected varied in chemical composition and con-tained 0–90% aNDF, 1–16% ash, 1–20% crude fat, 1–40% crude protein, and 0–50% starch. Cor-recting results for changes in blanks and reporting results as ash-free aNDF organic matter (aNDFom) improved the repeatability and reproducibility of results when aNDF was <25%. The within-labora-tory repeatability standard deviation (s r) for per-centage aNDFom in feeds varied from 0.21 to 1.82 and among-laboratory reproducibility standard de-viation (s R) varied from 0.37 to 2.24. The HORRAT was <2 for all materials except feed materials con-taining >10% fat. However, standard deviations of repeatability and reproducibility for feeds with >10% fat were similar to those of other materials. It is recommended that the aNDF method be ac-cepted for Official First Action status.
The objective of this paper is to quantify the magnitude of the major sources of variation, which affect in vitro digestibility (DMD) and concentrations of neutral detergent fibre (NDF), acid detergent fibre (ADF), and crude protein (CP) of annual pastures in Mediterranean-type climate zones. Four experiments were conducted in the south-west of Western Australia in 200607 and 200708, where the supply of nitrogen, phosphorous, potassium, or sulfur and pasture types were varied. Effects of seasonality, fertiliser application, pasture type, and site were analysed with an auto-regression maximum likelihood procedure. Temperature sum was used to explain the seasonal differences in DMD, CP, NDF, and ADF. Seasonality explained 82, 79, 79, and 62% of the total variation in DMD, NDF, ADF, and CP, respectively, with only an additional 5, 5, 6, and 24% being explained by the combined effects of site/management, fertiliser application, and pasture type. The differences in DMD, NDF, ADF, and CP, between sites, were 2.36.0%, 4.618.7%, 5.88.6%, and 1.517.4%, respectively. Pasture types differed by 6.69.5%, 9.011.4%, 3.16.1%, and 5.15.2% for DMD, NDF, ADF, and CP, respectively. The differences between sites and pasture types were markedly larger for CP, NDF, and ADF than for DMD. Fertiliser application did not affect nutritive characteristics, with the exception of N application rates on CP. It was concluded that the seasonality model captured nearly all of the temporal variation in DMD, NDF, and ADF but not in CP. The spatial variation in DMD was mostly determined by pasture type. By comparison, NDF and ADF were most strongly affected by grazing management, and CP by the availability of N.
Few validated studies have tested the n-alkane method for diet estimation in non-ruminants and the technique has rarely been validated for estimating diet composition for more than two dietary components. The arboreal marsupial Trichosurus vulpecula was fed leaf and fruit diets with up to five component species in two trials. In Trial 1, alkane recovery was estimated, and in Trial 2 these estimates were used to predict digestibility, diet composition and dry matter intake. Alkane recovery increased non-linearly (convex up) with increasing n-alkane chain length. Recovery was linearly and negatively correlated with diet digestibility and appeared to explain a progressive bias with observed digestibility in the alkane estimates of digestibility (slope = 0.37). Diet composition was successfully estimated for up to five leaf dietary components without correction for recovery. Correcting for recovery gave less reliable diet-composition predictions, indicating that the recovery estimates could not be extrapolated to the second trial. Dry matter intake appeared to be relatively robust to variation in alkane recovery between individuals (mean bias =1.6%). If recovery is shown to vary with digestibility in other taxa, calibration of the alkane technique will require diet- and taxon-specific calibration trials to give reliable estimates of diet composition and dry matter digestibility.
A study of rhizosphere physical-chemical and biological properties for dominant vegetation, including Stipa tenacissima and Rosmarinus officinalis, and for relict natural vegetation, namely Olea europaea subsp. sylvestris, Pistacia lentiscus, Retama sphaerocarpa, and Rhamnus lycioides, was carried out in an abandoned agricultural soil from a semiarid Mediterranean area. Rhizospheres of R. sphaerocarpa and S. tenacissima had the highest concentration of total N. Rhizospheres of R. sphaerocarpa and R. lycioides showed the highest soluble C-fraction values (water soluble C and water soluble carbohydrates). The highest percentages of stable aggregates were recorded in the rhizospheres of P. lentiscus (about 69%) and S. tenacissima (about 79%). O. europaea and R. sphaerocarpa had the highest capacity to enhance the development of mycorrhizal propagules in their rhizospheres. The mycorrhizal potential of S. tenacissima was on average 3.2-fold lower than that of O. europaea and R. sphaerocarpa, which points to the necessity ofreconstituting it prior to carrying out revegetation processes.
The limitations of the alkane technique in estimating the diet components of herbivores call for the introduction of new diet composition markers. Recently, long-chain alcohols (alcohols) and long-chain fatty acids (acids) have received the most attention and show great potential, when combined with alkanes, to estimate composition of complex diets. In the current study, faecal recoveries of alcohols and acids were determined in sheep in four different live weight groups fed three herbage species, either Leymus chinensis, L. dasystachys or Elymus sibiricum. Analysis of variance (ANOVA) was used to examine the effects of herbage species and live weight of sheep on faecal recoveries of individual alcohols and acids. Further, an indoor experiment with six sheep fed a diet of equal proportions, on dry matter (DM) basis, of three herbages was performed, allowing to assess the accuracy of alcohols and/or acids in combination with alkanes, to estimate diet composition. A one-sample t-test was carried out to test the accuracy of these estimates. Results of the first experiment indicated that the faecal recoveries of alcohols and acids were significantly affected by herbage species (P < 0.05). While the effects were significant or near significant for the faecal recoveries of some alcohols (C24-ol, C30-ol and C26-ol) (P 0.05), no effect of live weight on faecal recoveries of acids was observed (P > 0.05). Therefore, adjustments based on diet-specific faecal recoveries might improve diet composition estimates. This was illustrated by the results of the second experiment. The diet composition estimated from alcohols or all combinations of alcohols with other marker types, after diet-specific correction of faecal recoveries, did not significantly differ from the actual composition (P > 0.05). However, using acids as additional markers resulted in poorer diet composition estimates. This study confirmed the utility of alcohols, combined with alkanes, as markers to estimate composition of complex diets. Although corrections based on mean faecal recoveries, average over animals and diets, resulted in some accuracy loss, results were still satisfactory and better than without recovery correction.
In a feeding trial with 24 sheep, we used the alkanes, long-chain alcohols (LCOH) or both of these plant wax markers, to estimate the diet composition of animals offered diets comprising alkane-labelled cottonseed meal (CSM) together with up to four forages. The diets used were: Diet 1 subterranean clover (Trifolium subterraneum); Diet 2 subterranean clover + phalaris (Phalaris aquatica); Diet 3 subterranean clover, phalaris + annual ryegrass (Lolium rigidum); and Diet 4 subterranean clover, phalaris, annual ryegrass + wheat straw (Triticum aestivum). Estimates of diet composition were made following correction of faecal alkane or LCOH concentrations for incomplete faecal recovery, using recovery estimates derived from individual animals, mean recoveries for a given dietary treatment or grand mean recoveries. Estimated dietary proportions of CSM and known intakes of CSM were used to estimate forage intake. The LCOH concentrations of the diet components were much higher than their alkane concentrations, especially for phalaris. Multivariate analyses showed that the discriminatory information provided by the LCOH was additional to that provided by the alkanes, and that a combination of (LCOH + alkanes) discriminated better between diet components than either class of marker alone. Faecal recoveries of LCOH increased with increasing carbon-chain length; there were no differences in recovery attributable to diet. The most accurate estimates of diet composition were obtained with the combination of (LCOH + alkanes). Estimates of diet composition based on LCOH alone were not as good as alkanes alone, due to the high correlation between the LCOH profiles of phalaris and ryegrass. Total grass content of the diet was very accurately estimated using LCOH. Diet composition estimates provided estimates of whole-diet digestibility, which did not differ from the measured values. Trends in the accuracy of forage intake estimates reflected those found with diet composition and almost two-thirds of estimates based on (LCOH + alkanes) had lower error than those found with alkanes alone. The results confirm that supplements labelled with plant wax components can be used to estimate forage intake, and also show that the LCOH are useful markers for estimating diet composition. Intakes were also computed using a combination of natural LCOH concentrations in the diet and the daily dose rate of even-chain alkanes administered by intra-ruminal device. Differences between intakes so estimated and the measured intakes were closely related to the difference in faecal recovery between the LCOH/alkane pair used to estimate intake, by an amount close to that expected on theoretical grounds. It is concluded that the use of plant wax LCOH, especially in combination with alkanes, will result in improved estimates of diet composition and intake in grazing animals.
To investigate the potential use of n-alkanes (alkanes), long-chain alcohols (alcohols) and long-chain fatty acids (acids) for estimating the diet composition of sheep, in a feeding trial. A total of 18 sheep were assigned randomly to three different diets (diet A, diet B and diet C) containing up to eight herbage species (Leymus chinensis, Leymus dasystachys, Elymus sibiricum, Chenopodium album, Puccinellia chinampoensis, Medicago sativa, Saussurea sinuata and Bromus inermis). Faecal recoveries of alkanes, alcohols and acids were determined, and diet compositions were estimated using different combinations of alkanes, alcohols and acids. The faecal concentrations of individual alkanes, alcohols and acids were corrected using the mean recovery of the dietary treatment that the respective animal belonged to (diet recovery), or the mean recovery across all dietary treatments (general recovery). In general, diets did not affect the faecal recovery values for alkanes, alcohols and acids, and no difference in accuracy was found between diet composition estimates based on dietary recovery and general recovery. The accuracy of diet composition estimates declined as the number of dietary components increased from four to eight herbage species (P < 0.001). Better (P < 0.05) estimates of diet composition were obtained with the combinations of two or three marker types instead of alkanes alone. Moreover, results showed that excluding minor diet components from the calculations decreased (P < 0.05) the accuracy of diet composition estimates, whereas including extra non-grazed herbage species did not reduce (P > 0.05) the quality of diet composition estimates. These results confirmed the usefulness of alkanes, alcohols and acids as markers for determining complex diet composition of sheep. However, a negative impact on the accuracy of diet composition estimates, caused by missing minor diet components from the calculation of diet composition, could happen when plant wax markers are used to estimate the diet composition of free-ranging animals.
The study was carried out at the communal rangeland in the community of Chenini, Southern Tunisia aiming at assessing the effect of the rest technique on plant cover dynamics and productivity. In both protected and grazed (control) rangelands, total plant cover, species richness as well as biomass production and range value were determined. The results showed considerable and positive effects of protection on the parameters scored. The short term protection (2 years only) permitted an increase of the rangeland production of about about 352000 forage units, an equivalent of 352 tones barley. In addition to the conservation of biodiversity and natural resources, the communal rangeland rest may be considered as an interesting technical option and tool to face the increase of animal feeding resources costs and to mitigate drought in Southern Tunisia.
Plant-wax markers can be used for estimating forage intake, diet composition and supplement intake in grazing livestock, wild ruminants and other mammals. We describe protocols for using the saturated hydrocarbons (alkanes) of plant wax as markers for estimating fecal output, intake and digestibility. Procedures for investigating digestion kinetics are also discussed. Alkanes can also be used to estimate diet composition and the procedures required to do this are also described, including the special case where supplementary feed is treated as a component of the diet composition estimate. The long-chain alcohols (LCOHs) and very long-chain fatty acids (VLCFAs) of plant wax show particular promise for discriminating a greater number of species in the diet. The use of all these plant-wax markers in nutrition studies depends on having quantitative, repeatable and mutually compatible assay procedures for alkanes, LCOHs and VLCFAs; we present protocols for these assays in detail. Analysis of a single sample of feces or plant material for all these plant-wax markers can be completed within 2 days; however, it is possible to process up to 50 samples (analyzed in duplicate) per week.
Utilization of long-chain alcohols (LCOH) as diet composition markers in horses and cattle was assessed in a study conducted with 12 mature crossbreed mares (385±47 kg BW) and six adult non-lactating cows (499±36 kg BW) of Asturiana de los Valles breed. The LCOH data were combined with alkane and long-chain fatty acid (LCFA) data to test the applicability of combining these markers to estimate diet composition. Animals were randomly divided into groups of three animals and received a daily total amount of 1.0 kg dry matter/100 kg BW of diets composed of different proportions of ryegrass (Lolium perenne) and woody species (Ulex gallii and heather). Diet composition was estimated from even-chain LCOH (C20-OH to C30-OH) combined or not with alkane (C25-C31 and C33) and/or LCFA (C22-FA to C28-FA, C30-FA, C32-FA and C34-FA) concentrations in diet components and faeces by least-squares procedures, using marker faecal concentrations uncorrected for incomplete faecal recovery (FR0) or corrected using mean recoveries across diets within animal species (FR1). Results showed large differences between plant species in their LCOH profiles, and that these markers offered additional discriminatory information to that provided by alkanes and LCFA. The LCOH markers were incompletely recovered in the faeces of both animal species. In cattle, LCOH FR tended to increase with carbon-chain length in a linear manner in both diets (P<0.001), whereas in horses overall data showed a curvilinear relationship between these variables. Combination of LCOH, LCFA and alkanes resulted in more accurate diet estimates. Correction of faecal LCOH concentrations to incomplete FR led to more accurate diet composition estimates in both animal species. Results obtained in this study suggest the usefulness of LCOH markers combined with alkanes and LCFA to estimate diet composition of horses and cattle grazing mixed grassy-woody plant communities.
This study indicated that the bite-count and fecal analysis methods give similar results for estimating major components of cattle diets in Texas. The bite-count method could not be used on large, brush-infested pastures with rough terrain; however, the fecal analysis method was easily used under such conditions. Other advantages of fecal analyses were: samples were collected with a minimum of field work, diets of wild and domestic animals could be obtained, and bad weather and poor field conditions were not problems. Major disadvantages of the fecal analysis technique were: forages with dense stellate trichomes were overestimated; mesquite beans were retained in the digestive tract for abnormally long periods; the laboratory phase required a trained technician; and the work was tedious.
This study aimed to evaluate the possible utilization of carbon isotope enrichments (δ13C) of n-alkanes as faecal markers for estimating diet composition of goats fed with diets composed of different proportions of browse (Erica umbellata, Erica cinerea, Calluna vulgaris, Erica arborea, and Ulex gallii) and herbaceous feeds (Lolium perenne and Trifolium repens). Diet composition was estimated from δ13C of n-alkanes (C27 and C29-C33) in plant species and faeces alone and/or their combination with alkanes, long-chain fatty acids and long-chain alcohols, using least square optimization procedures. Large variation between plant species in their δ13C profiles was observed with the level of enrichment varying from -31.20 ‰ to -38.40 ‰ and tending to be higher for the odd-chain δ13C compared to even-chain ones (-34.12 ± 1.90 ‰ vs. -35.13 ± 1.39 ‰, respectively). Results suggest that δ13C values of alkanes provided different discriminatory information to that given by other markers. No differences were found between the faecal recovery of 13C and 12C in individual alkanes, showing evidence that no differential degradation in the gastrointestinal tract occurred between isotopes for any of the alkanes. These results indicate that δ13C values of alkanes can be used without the need to apply any faecal correction factor as they are relative values. Accuracy of diet composition estimates based on δ13C data alone was lower (P < 0.05) than when using alkanes, LCFA and LCOH. Moreover, data showed that the inclusion of δ13C in the input data used in diet composition calculations resulted in lower (P < 0.05) accuracy of the estimates in several combinations. Results indicate limitations on the use of δ13C values of alkanes, possibly because differences between plant species in their profiles may have been not sufficiently wide to obtain accurate estimates of diet composition.
Utilization of long-chain alcohols (LCOH) as diet-composition markers in sheep consuming six diets composed of improved pasture species (Lolium perenne and Trifolium repens) with heather–gorse components (Erica spp., Calluna vulgaris and Ulex gallii) was evaluated. Twenty-four adult cross-bred sheep were housed in individual stalls. Diet composition was estimated from LCOH concentrations, combined or not with alkanes and long-chain fatty acid (LCFA) data using least-squares procedures. Prior to calculations, faecal concentrations were corrected using mean treatment (faecal recovery 1, FR1) recoveries and mean recoveries across diets (FR2). Estimates were compared with those obtained without faecal correction (FR0) and known values. Large differences between plant species and plant parts were found in LCOH patterns and total LCOH concentrations. LCOH provided complementary information to that given by alkanes and LCFA. Even-chain LCOH comprised the largest fraction, representing on average 0·894 of total concentrations. Faecal recovery was incomplete and tended to increase with carbon-chain length (CCL) in a curvilinear manner (FR = −7·872 + 0·580 × CCL − 0·010 × CCL2; P < 0·001; r2 = 0·752). Diet composition influenced (P < 0·001) LCOH recovery, although variability within (CV of 9·0%) and between (CV of 13·3%) diets was low. Accuracy of estimates was influenced (P < 0·001) by faecal-correction method and markers used, and the best estimate was obtained combining LCOH and alkanes. Improvement in estimate accuracy can be achieved if suitable correction of LCOH faecal concentrations is performed prior to calculations. Results indicated that LCOH showed lower dependence than alkanes and LCFA on the use of accurate faecal-correction data.
Few methods exist for estimating quantitatively the diet composition of free-ranging herbivores. The current study examined whether long-chain fatty alcohols (alcohols) or long-chain fatty acids (acids) could be used along with n-alkanes to allow reliable diet composition estimates to be made in herbivores consuming complex diets. Twelve Scottish Blackface wether sheep housed in metabolism crates were fed four different mixtures of three plant species (three animals per mixture) for a seven-period experiment. Concentrations of cuticular wax n-alkanes, alcohols and acids were estimated in samples of individual plant species, and the faeces from animals that consumed mixtures of these species. These concentrations were then used to calculate the dietary proportions of each species by a least-squares optimization procedure. To explore the differences between the estimation methods (individual markers and their combinations), the mean squares of errors (EMS) between the actual and predicted proportions of plant species were calculated.
In three out of the four mixtures, alcohols had the lowest discrepancies (lowest EMS values), followed by n-alkanes and then acids. Acids yielded the lowest discrepancy in one mixture and the highest in the others.
It is concluded that, for this particular set of mixtures, alcohols had great potential to estimate composition of complex diets. However, the estimation using acids was less good and n-alkanes were of intermediate potential. Estimation from the combination of the three marker classes was always better than using the poorest individual marker.
The use of plant alkane concentrations to measure diet composition of
herbivores has been shown to be a reliable technique in animals grazing
temperate, sown pastures that contain a relatively small number of plant
species. There is potential to develop this technique for use with free-range
animals foraging upon species-rich rangeland. In order for the technique to be
effective, the alkane concentration patterns (ACP) of the component species of
the diet must be distinct from one another. Common species of grasses from
southern Africa were analysed for their alkane concentrations in order to
evaluate the use of the alkane technique for measuring diet composition under
complex rangeland conditions. The alkane profiles were determined in different
plant parts from 40 grass species gathered during the wet season and 23
gathered during the dry season. Statistical analysis, using ANOVA, showed that
there were highly significant differences (P <
0.001) in the C 25, C 27 , C
29 C 31 , C
33 , and C 35 alkane
concentrations between flower head and stem during both the dry and wet
seasons. Similar statistical differences were apparent in the C
25 , C 27 , C
29 , and C 31 alkane
concentrations of leaf and stem during both seasons; differences in C
33 and C 35 concentrations were
significant but at a lower level (P < 0.01 and
P < 0.05, respectively). Differences in C
25 , C 27 , and C
29 alkane concentrations between flower head and leaf
were only significant (P < 0.001) during the wet
season. Statistical differences (P < 0.001)
between whole plant samples obtained in different seasons were due to changes
in the proportion of flower head, leaf, and stem. Cluster analysis often
showed less similarity between plant parts of the same species than between
whole plant samples of different species. It was concluded that ACPs measured
in the selected species were probably too similar and thus, plants could not
be identified using the alkane technique. However, it was possible to use the
alkane technique to determine the proportions of flower-head, leaf, and stem
in the diet.
1. In north-east Scotland on a mixed heather and grassland pasture grazed by sheep, 2 x 2 m areas of Calluna vulgaris heath and Deschampsia flexuosa grassland were artificially contaminated with 134Cs by soil injection. Estimates of the 134Cs intake by sheep were made on the basis of measurements of dry matter intake, diet composition and 134Cs concentrations in diet components, assuming that the whole pasture had been contaminated. 2. Dry matter intake by sheep was measured using a natural n-alkane of plant waxes and an orally administered n-alkane as markers. Diet composition was determined by a combination of botanical analysis of samples of ingested material and relationships between n-alkane patterns in faeces and ingested material. 3. From May to September the percentage of grasses in the diet of the sheep decreased from 74% to 10%, while the percentage of C. vulgaris increased from 1% to 77%. Over the same period dry matter intake decreased and the botanical composition of vegetation and diet became more similar. However, the similarity in botanical composition between vegetation and diet was overall relatively low. 4. The 134Cs concentrations of dietary components increased in the order: Erica cinerea shoots, herbaceous dead matter, dead shoots of C. vulgaris, grasses (D. flexuosa and Festuca ovina), broad-leaved grasses (Agrostis spp. and others), Carex pilulifera, non-flowering and flowering shoots of C. vulgaris. 5. Intake of 134Cs by sheep was markedly higher in July compared to May as a result of increased 134Cs concentrations in all dietary components and increased consumption of C. vulgaris. Intake of 134Cs did not change significantly between July and September despite a further increase in the percentage of C. vulgaris in the diet. This was predominantly due to a decline of 134Cs concentrations in the green shoots of C. vulgaris. Seasonal changes in diet composition strongly influenced the relative contribution of different vegetation components to the total 134Cs intake. C. vulgaris contributed 82% and 70% of the total 134Cs intake in July and September respectively, while grass species contributed 82% in May. 6. It was calculated that between May and September the sheep had utilized 72% of herbage produced on the grassland and 29% of heather shoots produced on the heath. Assuming that the whole pasture had been contaminated, this was equivalent to a removal through grazing of 0.9% on the grassland and 2% on the heath of the 134Cs injected into the soil. By taking the sheep off the pasture at the end of September approximately 0.08% of the injected 134Cs would be removed from the site via the body tissues of the sheep.
The use of plant-wax markers for estimating forage intake, diet composition and supplement intake in grazing/browsing sheep and goats is reviewed in relation to some of the shortcomings of pre-existing techniques. The saturated hydrocarbons (alkanes) of plant wax are well validated as markers for estimating intake. Alkane-based estimates of intake have the advantage of accommodating individual differences in digestibility and those arising from supplement/forage interactions. Alkanes can also provide an estimate of diet composition and hence the inputs required to estimate herbage intake. Total intake can thus be partitioned into intake of individual species. It is probable that the alkane approach to estimating diet composition can discriminate fewer species in the diet of sheep and especially goats, than these animals encounter in complex plant communities. We discuss approaches to coping with this issue, such as grouping species in diet composition estimates, and the use of other plant-wax markers as diet composition markers. The long-chain alcohols and fatty acids are shown to have particular promise for discriminating a greater number of species in the diet. We then discuss the estimation of supplement intake using plant hydrocarbons, as a special case of the estimation of diet composition. Finally, we demonstrate that when supplement intakes are known, alkane-based estimates of the supplement proportion in the diet can be used to estimate the intake of all dietary components, without the need to dose animals with synthetic alkanes.
The application of n-alkanes as faecal markers to estimate diet composition of equines and cattle was studied. Twelve mature crossbreed mares (385 ± 47 kg live weight – LW) and six adult non-lactating cows (499 ± 36 kg LW) of Asturiana de los Valles breed were divided in groups of three animals (H1, H2, H3 and H4 in equines and C1 and C2 in cattle) and housed in individual stalls. Animals received a daily total amount of 1.0 kg DM/100 kg LW of different experimental diets composed of herbaceous (Lolium perenne L.) and woody species (Ulex gallii Planchon and heather: Erica spp. and Calluna vulgaris L.). Diet composition varied among treatments: H1 and C1 – L. perenne as sole component; H2 and C2 – L. perenne (0.70) and heather (0.30); H3 – L. perenne (0.70) and U. gallii (0.30); H4 – L. perenne (0.40), heather (0.30) and U. gallii (0.30).
Alkanes can be used as natural markers for estimating diet composition, but a factor should be used to correct for incomplete recovery in faeces. Faecal alkane recovery rates may be influenced by diet and animal factors. However, little research has been conducted to evaluate the effects of herbage species and live weight of animals on faecal alkane recoveries. In the current study, faecal recoveries of alkanes were determined in sheep in four different live weight groups (from 20 to 40 kg) fed three plant species (Elymus
sibiricum, Leymus
chinensis and L.
dasystachys). In a second experiment, the accuracy of intake and diet composition estimates, using alkanes as faecal markers, was assessed by feeding known amounts of the same plant species as a three-component mixture. The results showed that faecal alkane recoveries were influenced significantly by herbage species (P<0·01), but no effect of live weight of animals was observed. Total dry matter intake was estimated correctly based on either C31:C32 or C29:C32 alkane pairs. With respect to estimators of E.
sibiricum intake, reasonable results could only be obtained if the faecal alkane concentration was corrected based on diet-specific faecal recovery. More accurate estimations were obtained only if the alkanes found in relatively higher concentrations were used in diet composition estimates instead of using all available alkanes. Due to lower alkane concentrations or similar alkane patterns of L.
chinensis and L.
dasystachys in the diet, estimates of diet composition of these two herbage species were significantly different from the actual ones (P<0·05), implying that other markers need to be used for accurate estimation.
In many terrestrial ecosystems, variation in aboveground net primary production (ANPP) is positively correlated with variation in interannual precipitation. Global climate change will alter both the mean and the variance of annual precipitation, but the relative impact of these changes in precipitation on mean ANPP remains uncertain. At any given site, the slope of the precipitation-ANPP relationship determines the sensitivity of mean ANPP to changes in mean precipitation, whereas the curvature of the precipitation-ANPP relationship determines the sensitivity of ANPP to changes in precipitation variability. We used 58 existing long-term data sets to characterize precipitation-ANPP relationships in terrestrial ecosystems and to quantify the sensitivity of mean ANPP to the mean and variance of annual precipitation. We found that most study sites have a nonlinear, saturating relationship between precipitation and ANPP, but these nonlinearities were not strong. As a result of these weak nonlinearities, ANPP was nearly 40 times more sensitive to precipitation mean than variance. A 1% increase in mean precipitation caused a À0.2% to 1.8% change in mean ANPP, with a 0.64% increase on average. Sensitivities to precipitation mean peaked at sites with a mean annual precipitation near 500 mm. Changes in species composition and increased intra-annual precipitation variability could lead to larger ANPP responses to altered precipitation regimes than predicted by our analysis.
A simple technique for the determination in vitro of the dry- or organic-matter digestibility of small (0·5 g) samples of dried forages is described. It involves incubation first with rumen liquor and then with acid pepsin. Using 146 samples of grass, clover and lucerne of known in vivo digestibility (Y), the regression equation Y= 0·99 X– 1·01 (S.E. ± 2·31) has been calculated, where X=in vitro dry-matter digestibility. This technique has been used for the study of the digestibilities of plant breeder's material, of the leaf and stem fractions of herbage and of herbage consumed by animals.
The antlion fauna was investigated by black-lighting in late spring and late summer at two sites in southern Tunisia, representing pre-Saharan acacia savanna and dwarf shrub semi-desert of the Sahara, respectively. The species compositions recorded differed very markedly between sites and seasons, with few species encountered in both habitats or in both collecting periods. Di-versity was distinctly lower at the semi-desert site, where only 21 species, but a high number of individuals, were caught, with a strong dominance of one species each in the two seasons. At the acacia savanna location, 26 species were found, a few of which may, however, be asso-ciated with adjoining biotopes of oasis vegetation, ravines and hillside grassland. The species assemblage of the savanna is compared to a previous, similarly rich sample from the same re-gion. Some taxonomic and faunistic remarks are given regarding the species collected.
The effects of different grazing intensities of heifers on sward parameters such as sward structure, plant species diversity, herbage growth and forage quality as well as individual live-weight gains and live-weight gains per pasture area were studied in an upland area in the northern part of the Czech Republic over 4 years (1998–2001). The sward was maintained at a target height of 5 and 10 cm under intensive (IG) and extensive (EG) grazing, respectively. The total biomass production was higher under the IG than the EG treatment. In the Czech upland conditions, double peak curves of biomass growth during the grazing season were more typical than curves with one high spring peak. Species that responded positively to both treatments were the predominately short growing Trifolium repens, Taraxacum spp., Veronica arvensis and Agrostis capillaris. Tall species like Senecio ovatus, Alopecurus pratensis, Elytrigia repens and Aegopodium podagraria were associated with unmanaged plots. Total crude protein contents and forage digestibility were higher under IG. The content of crude fibre showed a reverse effect. Seasonal live-weight output per hectare under IG was approximately 1.5 times higher than EG treatment. However, if state subsidies are included, EG can be more profitable under the current Czech conditions than IG and satisfies both farmers and nature conservation objectives.
1. Mechanisms that affect the spatial distribution of animals are typically scale‐dependent and may involve forage distribution. Forage quality and quantity are often inversely correlated and a much discussed trade‐off is whether or not to select for high‐quality forage at the expense of forage abundance. This discussion has rarely involved scale‐dependence or been applied to Northern browsing herbivores. At small spatial scales, browsers are assumed to select for the best quality forage. But, as high‐quality forage resources are often scarce and may become depleted, coarse‐scale habitat selection is assumed to be driven by forage availability.
2. To evaluate if moose selection for forage quantity and quality is scale‐dependent we modelled summer and winter habitat selection of 32 GPS‐marked female moose ( Alces alces ) at two spatial scales (landscape‐scale vs. within‐home range‐scale). We used mixed‐effects resource selection functions (RSFs) and landscape‐scale forage availability models of six tree species of varying quality for moose. We considered silver birch ( Betula pendula ), downy birch ( Betula pubescens .), Scots pine ( Pinus sylvestris ) as low quality browse species and rowan ( Sorbus aucuparia ), aspen ( Populus tremula ), willow ( Salix spp.) as high‐quality species.
3. As expected, the overall selection patterns for available browse biomass and quality varied across spatiotemporal scales. At the landscape‐scale, moose selected for habitat with high available browse biomass of low quality species while at the within‐home range‐scale moose selected for sites with the highest quality browse species available. Furthermore, selection patterns during summer remained fairly stable, while during winter, selection at the within‐home range‐scale switched from sites with high quality to sites with lower quality browse species which suggests depletion of high‐quality species. Consistent with expectations from seasonal resource depletion, site fidelity (bimonthly home range overlap) was much lower in winter than in summer.
4. Coarse‐scale habitat selection by moose as a function of forage variability revealed a scale‐dependent trade‐off between available browse quantity and browse quality. Moreover, resource depletion changed the winter selection criteria of free‐ranging moose and we demonstrate how the behavioural response to such a dynamic process can be inferred from RSFs.
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Evolution of ecological characteristics along a gradient of soil degradation in the South Tunisian rangelands
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Régime et comportement alimentaire du dromadaire dans son milieu naturel désertique en Algérie
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Manipulating grazing distribution
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