Comparative Studies of Diet Selection by Sheep and Cattle: The Hill Grasslands

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Abstract
(1) A comparative study was made of the seasonal variation in floristic composition of the diets selected by sheep and cattle grazing together on Agrostis-Festuca, Nardus, and Molinia grassland communities in southern Scotland [UK]. Fenced plots at each site were grazed in sequence with the experimental animals moved between sites as appropriate. (2) For each period at each site, sward biomass, species and morphological composition and canopy structure were characterized. Diet samples were collected from three to five oesophagealy-fistulated animals of each species from four to seven, separate, two-week periods of observation at each site over three years. (3) Sheep diets were more variable than cattle diets, both between and within animals, for all sites. Sheep and cattle differed significantly for almost all major dietary components; exceptions were Molinia leaf, grass sheath and dead material at the Molinia site. (4) At all sites in summer, sheep diets contained more forbs and less grass flowerstem than did cattle diets. (5) At the Agrostis-Festuca and Nardus sites, sheep diets contained more live components than did cattle diets on all sampling dates. At the Molinia site, sheep and cattle diets contained smaller proportions of live components in early summer, but in autumn after the Molinia and Holcus leaves died, sheep grazed other grass species and their diets contained less live components than those of the cattle which grazed Juncus spp. (6) At the Nardus site, both sheep and cattle preferentially grazed the Festuca and Deschampsia (from between the Nardus tussocks) and the small patches of broad-leaved grasses. The progressive reduction in herbage biomass and height on the preferred areas in successive grazing periods was associated with a marked increase the Nardus content of cattle diets but not sheep diets. (7) Differences between sheep and cattle diets were explicable by (i) a difference in the height at which the animals grazed in relation to differences in the distribution of plant species within the sward canopy, (ii) the greater ability of sheep to select from fine-scale mixtures; and (iii) the greater readiness of cattle to graze tall, more fibrous components. (8) The implications of the differences in diet selection between sheep and cattle for sward responses and grazing management are discussed.