Comparative Studies of the Ingestive Behaviour and Herbage Intake of Sheep and Cattle Grazing Indigenous Hill Plant Communities

(1) Groups of mature, non-lactating ewes and cows grazed together on a series of four grassy communities (a perennial rye-grass sward, and indigenous communities dominated by Agrostis-Festuca, Nardus and Molinia, respectively) and two dwarf shrub communities (Calluna vulgaris-Eriophorum vaginatum blanket bog and Calluna moor). The communities were grazed in random sequence over a period of 4 years, to provide information on seasonal variations in ingestive behaviour and herbage intake on each community. (2) Information on diet digestibility was obtained by sampling from animals fistulated at the oesophagus, and estimates of herbage organic matter intake were made from these measurements and from determinations of faecal output by chromic oxide dilution. (3) Estimates of diet digestibility were consistently higher on the rye-grass 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 rye-grass sward. (4) Diet digestibility values tended to decline progressively from spring to late autumn, but intakes were usually highest in summer. (5) Levels of 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. (6) 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. (7) Species differences in biting rate and grazing time were small. However, in the Molinia community sheep had particularly low bite rates and grazing times, and high levels of intake per bite. (8) There was a significant community x animal species interaction in herbage intake, the relative advantage of sheep being substantially greater on the shrubby than on the grassy communities. (9) These results are discussed in terms of the foraging strategy and habitat exploitation of the two species, and the adequacy of nutrient supply for productive animals from the alternative communities.