The ability of endocrine manipulation of the neonate to effect prolonged changes in body composition was examined. Treatment of lambs with recombinant bovine somatotropin (rbST) at doses of 0.1 or 0.3 mg/kg liveweight/day for 11 weeks from birth elevated circulating ST concentrations (P<0.01) but had no effect on circulating concentrations of insulin-like growth factor-1 or on liveweight gain compared with excipient-treated lambs. However, at 8 months of age (5 months after cessation of treatment), ultrasound backfat depths (Mean±SE) were significantly (P<0.05) higher in lambs previously treated with excipient (3.4±0.3 mm) than in those treated with rbST at 0.1 mg/kg (2.8±0.3 mm) or 0.3 mg/kg (2.5±0.3 mm). In a second study, rats were treated with saline vs. 0.2 ug/g rbST vs. 0.4 ug/g rbST vs. 0.2 ug/g pituitary ovine prolactin (poPRL) vs. 0.4 mu/g poPRL for the first 21 days of life. At 120 days of age they were euthanased, selected fat depots weighed and the carcasses analysed for fat content. Neonatal treatment with rbST or poPRL significantly (P<0.05) reduced weight of the subcutaneous scapular fat depot (1.08±0.18 vs. 0.46±0.17 vs. 0.52±0.18 vs. 0.50±0.17 vs. 0.49±0.17 g) and carcass fat content (5.88±0.27 vs. 5.03±0.26 vs. 4.58±0.27 vs. 5.28±0.26 vs. 4.70±0.26%) but did not influence weights of the subcutaneous abdominal, genital or perirenal fat depots. These results suggest that endocrine manipulation of the neonate may offer a means of producing desirable changes in the composition of production animals while avoiding consumer resistance to the use of hormonal growth promotants close to the time of slaughter.

SN, McCutcheon, IT Kadim, GA Wickham, and RW Purchas

Proceedings of the New Zealand Society of Animal Production, Volume 54, , 51-54, 1994
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