Factors limiting the intake of feed by sheep. 14. Comparisons of voluntary feed consumption and various transactions in the alimentary tract between lambs and sheep fed roughage diets

Abstract

Comparisons were made of the voluntary intake and digestion of diets based on chopped straw, chopped lucerne and ground lucerne by lambs (c. 23 kg body weight) and adult sheep (c. 53 kg), and of feed intake and digestion by larger lambs (c. 35 kg) and adult sheep (c. 53 kg) grazing senescent pasture. With both the chopped and ground diets the lambs (i) had digesta of finer texture, (ii) cleared larger particles (>600 ¦m sieve) more slowly from the rumen, (iii) cleared organic matter more rapidly from the omasum and caecum + proximal colon, and (iv) performed more rumination bites. With the chopped diets, digestibility and feed intake pcr unit metabolic body weight were similar for lambs and adults but the lambs (i) spent more time eating, (ii) had more digesta in the reticulorumen per unit reticulo-rumen digesta free body weight, (iii) clcarcd organic matter from the abomasum more rapidly, and (iv) had less ash in abomasal digesta (straw-based diet only). With the ground lucerne diet the lambs (i) consumed more feed per unit of metabolic body weight, (ii) regurgitated more rumination boluses and (iii) cleared organic matter more rapidly from the reticulorumen. At pasture, it was estimated that the lambs (i) consumed more feed per unit metabolic body weight, (ii) had more digesta in the reticulo-rumen per unit rcticulo-rumen digesta free body weight, (iii) clearcd organic matter more rapidly from the omasum and abomasum, (iv) tended to have digesta of finer texture and (v) had less ash in abomasal digesta (-64%). The differences between the lambs and adults and their possible implications arc discussed, and it is suggested that with lower-quality roughages the smaller lamb may be placed at a disadvantage, relative to the adult, because of an inability to exhibit a higher feed intake commensurate with its higher maintenance energy need.