A note on the effect of bulk density and digestibility on the voluntary intake of concentrate diets by sheep of two ages

Three pelleted diets based on rolled barley, whole oats and ground oats respectively were offered ad libitum to mature wethers and growing lambs. With wethers, intakes on the whole oat diet were significantly greater than on the barley diet but digestible dry-matter intakes were not significantly different. On average, growing lambs ate significantly greater quantities of the ground oat diet and whereas digestible dry-matter intakes on the ground oat and barley diets were not significantly different, both were higher than on the whole oat diet. Examined at successive live weights, intakes on the whole oat diet were, at 15 kg, initially lower than on the barley diet but were ultimately higher at 60 kg, when there were no significant treatment differences in digestible drymatter intakes.

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

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 (P<0·05) whereas gut contents increased from 9·9% of live weight to 16·1% (P< 0·001) from A to E. Differences in efficiency of utilization of ME above maintenance were variable but for gross efficiency (i.e. retention/total ME intake), there was a significant decline from A to E.

Dry-matter intakes for the whole experimental period were similar for all five diets, but initially intake was lower for diet E than for A (780v.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.