AN OVINE-GROWTH-HORMONE TRANSGENE MODEL SUITABLE FOR SELECTION EXPERIMENTS FOR GROWTH IN MICE

Because the oMT1a-oGH transgene in mice can be regulated by dietary zi nc, it provides a potential model for selection studies designed to in crease growth rate. To determine the effect of oMT1a-oGH on growth, fa t content, and reproduction in the genetic background and environment in which selection would be conducted, males homozygous for the transg ene were mated to females from high-growth (M16) and control (ICR) lin es to create hemizygous transgenics, TM and TC, respectively. Progeny either did (Z) or did not receive (C) 25 mM ZnSO4 from 3 (weaning) to 8 weeks. TM mice had larger (p<0.001) weekly body weights than TC from 3 to 10 weeks, and Z mice were larger than C from 5 to 10 weeks in TC and from 6 to 10 weeks in TM. Significant (p<0.001) line-treatment in teractions for weekly body weights from 4 to 8 weeks were caused by TC responding more to the transgene than TM mice. Compared to controls, male mice given zinc had reduced (p<0.001) epididymal and subcutaneous fat-pad weights as a percentage of body weight, but liver percentage was increased (p<0.001). TC mice given zinc had reduced (p<0.05) testi s weights as a percentage of body weight, while there was no differenc e in TM mice. TM mice had larger liver (p<0.01) and epididymal fat-pad (p<0.08) percentages than TC. Mating of Z females 2 weeks after disco ntinuation of zinc stimulation of transgene expression resulted in no significant differences between Z and C females in percentage infertil e matings, days from exposure to a male to littering, and number of de ad pups on day of birth; however, Z females had larger (p<0.007) litte rs. This transgenic model is suitable for selection studies involving growth. When transgene expression is stimulated by exogenous zinc, gro wth rate is increased and there is no negative effect on female reprod uctive fitness when zinc supplement is discontinued.