Resource heterogeneity and foraging behaviour of cattle across spatial scales

Santiago A Utsumi,Mary B Mceachern,Emilio A Laca,Montague W Demment,Julio R Galli,Carlos A Cangiano

doi:10.1186/1472-6785-9-9

Abstract

BackgroundUnderstanding the mechanisms that influence grazing selectivity in patchy environments is vital to promote sustainable production and conservation of cultivated and natural grasslands. To better understand how patch size and spatial dynamics influence selectivity in cattle, we examined grazing selectivity under 9 different treatments by offering alfalfa and fescue in patches of 3 sizes spaced with 1, 4, and 8 m between patches along an alley. We hypothesized that (1) selectivity is driven by preference for the forage species that maximizes forage intake over feeding scales ranging from single bites to patches along grazing paths, (2) that increasing patch size enhances selectivity for the preferred species, and that (3) increasing distances between patches restricts selectivity because of the aggregation of scale-specific behaviours across foraging scales.ResultsCows preferred and selected alfalfa, the species that yielded greater short-term intake rates (P < 0.0001) and greater daily intake potential. Selectivity was not affected by patch arrangement, but it was scale dependent. Selectivity tended to emerge at the scale of feeding stations and became strongly significant at the bite scale, because of differences in bite mass between plant species. Greater distance between patches resulted in longer patch residence time and faster speed of travel but lower overall intake rate, consistent with maximization of intake rate. Larger patches resulted in greater residence time and higher intake rate.ConclusionWe conclude that patch size and spacing affect components of intake rate and, to a lesser extent, the selectivity of livestock at lower hierarchies of the grazing process, particularly by enticing livestock to make more even use of the available species as patches are spaced further apart. Thus, modifications in the spatial pattern of plant patches along with reductions in the temporal and spatial allocation of grazing may offer opportunities to improve uniformity of grazing by livestock and help sustain biodiversity and stability of plant communities.

Highlights

Understanding the mechanisms that influence grazing selectivity in patchy environments is vital to promote sustainable production and conservation of cultivated and natural grasslands
Preferences were constrained under the 9 treatments, resulting in a lower selectivity index compared to preference (Table 2)
When integrating behaviors along the grazing process, cumulative selectivity increased from patch encounters to total intake, but became significant only when bite formation and mass were included as final steps in the grazing process (Table 2)

Summary

Introduction

Understanding the mechanisms that influence grazing selectivity in patchy environments is vital to promote sustainable production and conservation of cultivated and natural grasslands. A better understanding of the mechanisms governing forage preference and selectivity in patchy, heterogeneous environments is needed to inform new management approaches that enhance grazing distribution at spatial sales ranging from bites to patches [3]. Preferences are traditionally determined by offering accessible amounts of alternative forage and comparing forage intake. Selectivity, on the other hand, is a measure of forage intake under patchy, heterogeneous conditions where alternative forages are not available or uniformly distributed [5]. In this context, selection of preferred forage can often be constrained by environmental and physiological tradeoffs [4,5]. Depending on the trade-offs involved, selectivity will not necessarily coincide with preference

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