Effects of dietary protein and β-agonist on growth and fat deposition in prepubertal lambs
Weaned female lambs were used to study the effects of dietary protein (15 or 20%) and β-agonist (L-644,969: 0 mg kg−1 or 1 mg kg−1) on fat deposition between weaning and puberty. Lambs were fed pelleted concentrate plus 200 g hay d−1 to achieve a target weight gain of 260 g d−1. The trial continued for 102 d with dietary protein treatment starting on day 1 and β-agonist starting on day 20. Comparisons were made between the two levels in each of the two factors when there was no interaction. Carcass fat was reduced by 19.1% (P < 0.01) and carcass protein was increased by 15.8% (P < 0.01) in lambs fed the β-agonist. Carcass fat and protein were not affected by dietary protein. There was a nonsignificant trend to lower kidney-pelvic fat and subcutaneous fat thickness with the β-agonist (P > 0.1). Treatment did not affect the total mammary-gland weight, expressed as a proportion of final body weight. Neither the diameter nor the number of fat cells in kidney–pelvic fat and the MGFP were affected by dietary protein or β-agonist. Results indicate that the β-agonist is effective in the control of fat deposition other than that in the MGFP in rapidly growing female lambs. However, there was no apparent effect of dietary protein on adipose tissues. Key words: Lambs, β-agonist, dietary protein, fat deposition