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 zinc, it provides a potential model for selection studies designed to increase growth rate. To determine the effect of oMT1a-oGH on growth, fat content, and reproduction in the genetic background and environment in which selection would be conducted, males homozygous for the transgene were mated to females from high-growth (M16) and control (ICR) lines 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 interactions 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) testis weights as a percentage of body weight, while there was no difference 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 discontinuation of zinc stimulation of transgene expression resulted in no significant differences between Z and C females in percentage infertile matings, days from exposure to a male to littering, and number of dead pups on day of birth; however, Z females had larger (p<0.007) litters. This transgenic model is suitable for selection studies involving growth. When transgene expression is stimulated by exogenous zinc, growth rate is increased and there is no negative effect on female reproductive fitness when zinc supplement is discontinued.