GROWTH, FEED-EFFICIENCY AND BODY-COMPOSITION OF TRANSGENIC MICE EXPRESSING A SHEEP METALLOTHIONEIN 1A-SHEEP GROWTH-HORMONE FUSION GENE

Growth, feed efficiency and body composition were studied in male mice possessing a sheep metallothionein la-sheep growth hormone transgene (oMT1a-oGH). The transgene was activated at weaning (21 d) by 25 mM zinc sulfate provided in drinking water. Body weight and feed intake were measured at weekly intervals until 70 d. Transgenic males gained 53.3% more weight than controls during the test period (P<0.001) while consuming only 10.9% more feed (P<0.001). When adjusted for metabolic body weight, feed intake was similar for the two genotypes. Transgenics had more epididymal and subcutaneous fat at 70 d (P<0.001), but less fat at both depots (P<0.05) when adjusted to a common body weight. Lean tissue, estimated by trimmed hind carcass weight, was greater in transgenics when compared at a common age (P<0.01) but lower when compared at a common body weight (P<0.001). If analyzed for a common weight pin, transgenics exhibit much higher efficiency of lean tissue production, due to a much lower intake required to produce lean. Visceral organs were heavier in transgenics than in controls, but only liver and spleen exhibited disproportional enlargement relative to overall body size increases (P<0.001). These results demonstrate that mice possessing an oMT1a-oGH transgene exhibit increased efficiency of growth and of lean tissue production, especially when considered over a standard weight pin period.