Evaluation of 3 techniques for determining diet composition

Henley, S. R.; Smith, D. G.; Raats, J. G.

doi:10.2458/azu_jrm_v54i5_henley

Cited by 14 publications

(25 citation statements)

References 16 publications

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“…The density dependence observed in diet was robust to the methodology used, as both direct observation and microhistological analyses of diet composition yielded similar results. However, the absolute values obtained by these two methods differed, as faecal analyses tended to underestimate the proportion of easily digestible plants such as many forbs, whereas grasses and especially shrubs may be overestimated (Stewart & Stewart, 1970; Kessler et al , 1981; Mofareh, Bech & Schneberger, 1997; Henley et al , 2001). On the other hand, it can be very difficult to obtain unbiased estimates by direct observation, as some plants are removed completely, leaving no observable bite marks.…”

Section: Discussionmentioning

confidence: 99%

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Density‐dependent foraging behaviour of sheep on alpine pastures: effects of scale

Kausrud

Mysterud

Rekdal³

et al. 2006

Journal of Zoology

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Foraging patterns of large herbivores may give important clues as to why their life history varies depending on population density. In this landscape-scale experiment, domestic sheep Ovis aries were kept at high (80 sheep km À2 ) and low (25 sheep km À2 ) population densities during summer in high mountain pastures in Hol, Norway. We predicted an increasing use of less preferred plant species or habitat types with increasing sheep population density. Foraging behaviour was investigated by direct observations of individually marked sheep on different spatial scales, and diet composition was also assessed with microhistological analysis of faecal samples from known individuals. We found that the effects of density on foraging behaviour depended on scale and were only detected at the scale of diet choice. Use of the common grass species Deschampsia flexuosa, which provided the bulk forage (10-65% of the diet), remained constant throughout the season at low densities, but increased significantly over time at high densities. On a coarser spatial scale, neither within vegetation type nor between vegetation types, selection was affected by density, but vegetation type selection differed depending on whether the sheep were grazing or resting. Our study provides evidence of density dependence in foraging behaviour, but only at the finest spatial scale (diet choice).

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Section: Discussionmentioning

confidence: 99%

“…Determining the diet of ungulates in field studies is difficult, as all methods have their different biases (e.g. Gaare, Sørensen & White, 1977;Kessler, Kasworm & Bodie, 1981;Henley, Smith & Raats, 2001). We therefore used two methods (direct observation and faecal analysis) to assess dietary choice.…”

Section: Fine-scale Foraging: Dietmentioning

confidence: 99%

Density‐dependent foraging behaviour of sheep on alpine pastures: effects of scale

Kausrud

Mysterud

Rekdal³

et al. 2006

Journal of Zoology

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“…Since it was impossible to distinguish consumption signs on herbs in the field, we evaluated the preference of herbivores for different resources (woody versus herbaceous species) using microhistological analysis of plant remains in faecal samples (Holechek et al 1982;McInnis et al 1983;Putman 1984;Henley et al 2001). Fresh faeces were collected during spring 2006 and in winter 2006 and 2007 from the three ungulate species.…”

Section: Laboratory Analysesmentioning

confidence: 99%

Seasonality and edge effect determine herbivory risk according to different plant association models

et al. 2010

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We report evidence of hierarchical resource selection by large herbivores and plant neighbouring effects in a Mediterranean ecosystem. Plant palatability was assessed according to herbivore foraging decisions. We hypothesize that under natural conditions large herbivores follow a hierarchical foraging pattern, starting at the landscape scale, and then selecting patches and individual plants. A between- and within-patch selection study was carried out in an area formed by scrubland and pasture patches, connected by habitat edges. With regard to between-patch selection, quality-dependent resource selection is reported: herbivores mainly consume pasture in spring and woody plants in winter. Within-patch selection was also observed in scrub habitats, influenced by season, relative patch palatability and edge effect. We defined a Proximity Index (PI) between palatable and unpalatable plants, which allowed verification of neighbouring effects. In spring, when the preferred food resource (i.e. herbs) is abundant, we observed that in habitat edges large herbivores basically select the relatively scarce palatable shrubs, whereas inside scrubland, unpalatable shrub consumption was related to increasing PI. In winter, a very different picture was observed; there was low consumption of palatable species surrounded by unpalatable species in habitat edges, where the latter were more abundant. These outcomes could be explained though different plant associations described in the literature. We conclude that optimal foraging theory provides a conceptual framework behind the observed interactions between plants and large herbivores in Mediterranean ecosystems.

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“…A lot of methods have been used until now to evaluate ruminant diet selection under grazing systems [e.g., faecal analysis, esophageal fistulation (Papachristou and Nastis, 1993;Henley et al, 2006;Mellado et al, 2012), direct observation of grazing animals (Dumont and Boissy, 2000;Foroughbakhch et al, 2013;Mancilla-Leytón et al, 2013) and direct estimation of grazing damage of each species (Hejcman et al, 2008;Nagaike, 2012)]. However, in the current study the BR percentage of the whole flock on the half-long term was evaluated fitting the method proposed by Nagaike (2012) to the vertical point-quadrat method.…”

Section: Vegetation Surveys Browsing Ratio and Species Intake Assessmentioning

confidence: 99%

Browsing ratio, species intake, and milk fatty acid composition of goats foraging on alpine open grassland and grazable forestland

Iussig

Renna

Gorlier

et al. 2015

Small Ruminant Research

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Aims of this study were to investigate diet selection of dairy goats foraging on two alpine vegetation types and to assess the related effects on milk fatty acid (FA) composition. Two enclosures laid out on an open grassland (OG) and a grazable forestland (GF) were exploited by 14 Camosciata goats. A commercial concentrate was supplemented during milking. Forty-five plots were randomly selected inside each enclosure and used to assess the species relative abundance (SRA) and phenological stage of plants, as well as goats' preferences (browsing ratio, BR) and intake (SI) for each species.Representative samples of the diet in each enclosure were built up considering the most ingested plant species and plant parts. Feed samples were analyzed for proximate, FA, and phenolic compositions.Milk samples were collected in each enclosure and analyzed for their FA profile. The enclosures showed a similar level of vegetation diversity. If compared to the GF enclosure, the OG one had higher proportion of Poaceae (81.2 vs 44.8% of SRA) and lower proportion of non-legume dicotyledons (14.6 vs 50.7% of SRA). The goats mostly selected eutrophic species in OG and forbs and woody species leaves in GF. The ingested vegetation was almost completely represented by grasses in OG (89.6% of SI), and by similar proportions of grasses and herbs and woody species in GF (54.9 and 45.1% of SI, respectively). The ingested forages from the OG and GF showed a comparable proximate composition; if compared to OG, the GF vegetation type was however richer in α-linolenic acid (ALA) and phenolic compounds (PC). Fatty acid analysis showed that GF milk had higher concentrations of ALA, total omega-3 FA, total trans-octadecadienoic acids, total conjugated linoleic acids, total trans-octadecenoic acids, and a reduced omega-6/omega-3 FA ratio than OG milk.Branched-chain FA were not significantly affected by treatment, suggesting that the activity of ruminal bacteria in the goats was not inhibited by the higher concentration of PC in GF plants. The main reason for the observed improvement of the FA profile in GF milk seems to be attributable to the FA profile rather than the concentration and composition of PC of the ingested plants. The abundance of herbs and woody species in the ingested vegetation was positively associated with the presence of nutritionally desirable FA in goat milk fat.

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Evaluation of 3 techniques for determining diet composition

Cited by 14 publications

References 16 publications

Density‐dependent foraging behaviour of sheep on alpine pastures: effects of scale

Density‐dependent foraging behaviour of sheep on alpine pastures: effects of scale

Seasonality and edge effect determine herbivory risk according to different plant association models

Browsing ratio, species intake, and milk fatty acid composition of goats foraging on alpine open grassland and grazable forestland

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