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Department of Animal Science, Lilly Hall, Purdue University, West Lafayette, IN 47907 * Pittman-Moore, Inc., Terre Haute, IN
Eighty barrows were used in a 2 x 2 x 4 factorial experiment to examine the effects of genetic line (Hampshire x Yorkshire, H x Y, and Yorkshire x Landrace, Y x L), somatotropin (dose, 0 and 5 mg/d) and energy intake (ad libitum, 93%, 86% and 80%) on growth performance and energy requirements for lean gain over the finishing phase of growth. Four diets were formulated to maintain equal intakes of protein, vitamins and minerals at different energy intakes. Somatotropin increased growth rate 30 to 35% across diets despite an 8 to 12% reduction in ad libitum feed intake. Lean growth rate (kg/d) was increased preferentially by ST in the faster-growing H x Y barrows, which showed a 2.8-fold greater maximum rate increase than the slower-growing Y x L barrows. In control barrows, 10% reductions in energy intake had no effect on lean gain and improved feed/lean gain about 10%. In somatotropintreated barrows, lean gain was reduced with each energy restriction in H x Y; energy intake had no effect on lean gain in Y x L barrows. Feed/lean gain was improved 22% in Y x L barrows at the lowest energy intake. Data indicate that somatotropin accentuates breed differences in lean gain and energy requirements. Pigs with low lean-growth potential will benefit from restricted feeding, whereas strategies to increase energy intake in pigs with high lean-growth potential may be desirable.
KEY WORDS: pigs somatotropin genotypes energy requirements
1 A preliminary report of this research was presented at the 81st Annual Meeting of the American Society of Animal Science, July 31August 4, 1989, in Lexington, KY [Nossaman, D. A., Schinckel, A. P., Miller, L. F. & Mills, S. E. (1989) Effects of energy intake and porcine somatotropin on growth performance and carcass composition in two genetic lines of finishing pigs. J. Anim. Sci. 67 (Suppl. 1): 259 (abs. 633)].
2 Work supported in part by Central Soya, Decatur, IN, Pitman-Moore, Inc., Terre Haute, IN and the Indiana Pork Producers Association.
3 Journal paper No. 12548 of the Purdue Univ. Agric. Exp. Sta., West Lafayette, IN.
4 Present address: Land O'Lakes, Inc., Leighton, IA.
5 To whom reprint requests should be sent.
Manuscript received 27 June 1990. Revision accepted 27 August 1990.
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