a1 North of Scotland College of Agriculture, 581 King Street, Aberdeen AB9 1UD
a2 Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB
a3 Scottish Agricultural Statistics Service, Kings Buildings, University of Edinburgh, Edinburgh EH9 3JZ
The effect of undegradable protein supply was studied in overfat lambs given low-energy diets to reduce carcass fatness. Two trials involving sequential batches of 48 overfat Suffolk × lambs investigated the effects of supplementing an ad libitum straw diet with either 0 or 100 g fish-meal pellets daily for 14-, 28- and 42-day periods. Lambs supplemented with fish meal in trials 1 and 2 lost significantly less weight. Weight losses (g/day) were - 2 v. -129 (s.e.d. 26) and -5 8 v. -188 (s.e.d. 29) respectively. There were highly significant and favourable effects of fish-meal supplementation on carcass weight and composition (recorded in the second trial only). Carcass weight (kg) after 14, 28 and 42 days was 21·8, 20·4 and 18·3 for unsupplemented lambs and 22·4, 21·9 and 21·6 for supplemented lambs; saleable lean (kg) as determined by a commercial boning-out process was 12·1, 11·3 and 10·0 v. 12·7, 12·6 and 12·3 respectively. There were corresponding changes in conformation but fat trimmed off the carcass was not significantly reduced by the dietary treatments. There was, however, a reduction by one-fifth in excess carcass fat (about 0·5 kg) over the period 14 to 42 days on trial, and over the trial as a whole, fat trim fell from an estimated proportion of carcass weight of 0·17 to 012, equivalent to a fall in Meat and Livestock Commission fatness score from 4H to 3L. Results indicated very favourable financial rewards for supplementing diets of overfat lambs with fish meal.
(Received April 16 1988)
(Accepted August 01 1988)
p1 Present address: East of Scotland College of Agriculture, APAD, Bush Estate, Penicuik. Midlothian