EFFECTS OF DIETARY-PROTEIN AND BETA-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 beta-agonist (L-644,969: 0 mg kg(-1) or 1 mg kg(-1)) o n fat deposition between weaning and puberty. Lambs were fed pelleted concentrate plus 200 g hay d(-1) to achieve a target weight gain of 26 0 g d(-1). The trial continued for 102 d with dietary protein treatmen t starting on day 1 and beta-agonist starting on day 20. Comparisons w ere 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 ca rcass protein was increased by 15.8% (P < 0.01) in lambs fed the beta- agonist. Carcass fat and protein were not affected by dietary protein. There was a nonsignificant trend to lower kidney-pelvic fat and subcu taneous fat thickness with the beta-agonist(P > 0.1). Treatment did no t 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 be ta-agonist. Results indicate that the beta-agonist is effective in the control of fat deposition other than that in the MGFP in rapidly grow ing female lambs. However, there was no apparent effect of dietary pro tein on adipose tissues.