Selection of roughage diets by sheep and goats
The objective of the present work was to elucidate some of the possible choice determinants involved in diet selection by sheep and goats. The first experiment investigated the ingestive and digestive responses of these two species to a range of forage chemical composition attributes (i.e. nitrogen and fibre content). Forage DM intake was positively associated with their nutritive quality. Goats had higher voluntary DM intakes (P<0.05) and lower apparent digestibility coefficients (P<0.001) for any given forage than sheep, but the intake of digestible DM was similar for the two species. When forages were offered in pairs in a preference trial, the two species ranked forages similarly by favouring those of higher nutritive quality. The second experiment investigated the effects of different staple lengths of a single hay on the ingestive and digestive responses of sheep and goats. Goats had higher voluntary DM intakes (P<0.05) and lower apparent digestibility coefficients (P<0.001) for any given length than sheep, but the intake of digestible DM was similar for the two species. Goats allocated less time (P<0.001) than sheep to chewing the feed consumed and the mean retention time of the undigested residues in the animals' digestive tract was significantly shorter (P<0.01) for goats than sheep. When staple lengths of the grass hay were offered in pairs none of them was favoured and the choices were not significantly different between goats and sheep. In a third experiment a new method of feed presentation was developed and compared with conventional feed-bins. Goats had higher voluntary intakes than sheep (P<0.05), whereas there was no effect of the feed presentation method on DM intake.