Effects of genotype on the performance and intake characteristics of sheep grazing contrasting hill vegetation communities

Abstract

The live-weight responses, voluntary herbage intakes and diet compositions of two breeds of sheep of different mature live weights, grazing two contrasting hill vegetation communities, were studied over three consecutive grazing seasons. A total of 228 Latxa and 255 Gallega non-lactating ewes, with mature live weights of 42.4 and 33.1 kg respectively, grazed two replicates, each of two 5-ha plots comprising by area either 0.3 Calluna vulgaris and 0.7 grass species (Agrostis capillaris, Festuca rubra and Nardus stricta) (treatment C3) or 0.7 C. vulgaris and 0.3 of the above grass species (treatment C7). The Latxa ewes achieved higher rates of live-weight gain than the Gallega ewes under conditions of high availability (sward surface height >3.0 cm) of the preferred grass species (A. capillaris and F. rubra) but had lower rates of live-weight gain in the later part of the grazing season when the availability of the preferred grass species was low. In general, the Latxa ewes had higher voluntary herbage intakes per unit live weight and selected a diet of higher digestibility than the Gallega ewes (P<0.001). The composition of the diet was significantly affected by treatment (P<0.001) and was of a higher digestibility in the earlier part of the grazing season (P<0.001). The results indicate the existence of a significant (P<0.001) genotype X environment interaction affecting diet selection and animal performance. Between-breed differences in diet selection are likely to be important in determining grazing behaviour and thus the suitability of different genotypes for particular environments. Breeds with a small body size are likely to be better suited to the poorer land resources where the availability of preferred species is low.