Comparative studies of the ingestive behaviour and herbage intake of sheep and cattle grazing indigenous hill plant communities.
In field studies in Scotland, groups of non-lactating ewes and cows grazed together on 3 native grassland communities (Agrostis-Festuca, Nardus-Festuca-Deschampsia and Molinia), an established sward dominated by Lolium perenne, and 2 dwarf shrub communities (Calluna vulgaris-Eriophorum vaginatum blanket bog and Calluna moor). The communities were grazed in random sequence in 1987-90. Diet digestibility estimates were consistently higher on the L. perenne sward than on the indigenous grassy communities, and substantially higher on grassy than on dwarf shrub communities. Herbage intakes were also substantially higher on grassy than on dwarf shrub communities and were higher on the indigenous grassy communities than on the L. perenne swards. Diet digestibility values tended to decline progressively from spring to late autumn, but intakes were usually highest in summer. Bite rate and intake per bite were lower on dwarf shrub than on grassy communities. Overall, the results indicated the dominant influence of intake per bite on daily herbage intake. The sheep consistently maintained higher diet digestibility than did the cattle. Variations in diet digestibility were lower for sheep than for cattle both within and between periods, but the reverse was the case for variations in biting rate and intake per bite. Species differences in biting rate and grazing time were small, but sheep had particularly low bite rates and grazing times, and high levels of intake per bite in the Molinia community. There was a significant community × animal species interaction in herbage intake, the relative advantage of sheep being substantially greater on the shrubby than on the grassy communities. The results are discussed in terms of the foraging strategy and habitat exploitation of the 2 species, and the adequacy of nutrient supply for productive animals from the alternative communities.