Effect of increased production of growth hormone on body composition in mice: transgenic versus control.

The body composition (water, fat, protein and ash) of male and female transgenic mice which had a sheep metallothionein 1a-sheep growth hormone fusion gene and their non-transgenic controls was determined at intervals from birth to 21 days of age (weaning) in 66 mice of each group, and in an additional 64 mice over the period 25 to 98 days of age. Overall 520 mice were analysed. Weaned mice were starved overnight prior to slaughter. Food was available ad libitum. and, after weaning, a zinc sulphate supplement was added to the drinking water to initiate expression of the transgene. Growth and body composition were similar in all groups before weaning. From 39 days of age, transgenic females became progressively heavier than corresponding controls, being 60% heavier at the end of the experiment. They contained less fat, more water and slightly less ash than did controls of the same live weight but similar amounts of protein. When examined on a fat-free basis, they had less protein and ash and more water than corresponding controls. Appropriate linear and quadratic regression equations are presented to describe the above relationships. Growth and body composition were more variable in transgenic males but, on average, similar to controls.