The effect of different dietary energy concentrations on the voluntary intake and growth of intensively-fed lambs

Abstract

In a comparative slaughter trial which covered growth from about 16 kg to 40 kg live weight, five groups of six Romney × Swaledale lambs were offeredad libitumfive pelleted diets (A to E) in which rolled barley was gradually replaced by an 80 : 20 mixture of rolled oats : oat husks to the extent that the calculated metabolizable energy (ME) concentration fell from approximately 2–9 (A) to 2·5 (E) Mcal/kg DM.Although daily live-weight gains did not differ significantly between treatments, the daily carcass gain fell from 143 g/day on A to 105 g/day on E (Pv.927 g/day) and ultimately it was higher for E (1410v.1150 g/day). In a second experiment, involving diets A and E and a third diet of chopped dried grass, the pattern of intake and growth changed with live weight in a similar manner to that described above, except that appetite and growth on dried grass were consistently poorer. Daily variation in intake and rumen pH tended to be greater on the concentrate diets.It is suggested that, amongst other factors, the stage of maturity of an animal may influence the point at which the digestible energy content of the diet restricts dietary intake in preference to physical limitations.