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Summary To examine reproductive performance during lifetime in mice with and without the rat-growth-hormone transgene, transgenic and non-transgenic males and females were pair mated at about 8 weeks of age to form four mating groups (+/- × +/-, +/- × -/-, -/- × +/- and -/- × -/-). Pair breeders were maintained continuously in the same cages throughout their life. Reproductive longevity (days from the first cohabitation to the last parturition), litter size, and parturition intervals were recorded for each pair. The relative contribution of five interval-related variables to reproductive longevity, and the total number of 18-day young per breeding pair, were evaluated, using standardized partial regression coefficients. Correlation coefficients between the reproductive longevity and total number of 18-day young were moderate, ranging from 0.58 to 0.74 in the four mating groups. Mean reproductive longevity was longest (153.5 days) in -/- × -/-, followed by +/- × -/- (137.4 days), -/- × +/- (92.9 days), and +/- × +/- (82.0 days), indicating reproductive impairment of transgenic mice. Weight gain from 3 to 12 weeks of age differed significantly between transgenic and non-transgenic mice. The four mating groups had similar rankings, in terms of the total number of young born per pairs during a lifetime and reproductive longevity. When the parturition intervals of breeding pairs within groups varied greatly during a lifetime, they tended to have a shorter reproductive longevity. On the otherhand, when breeding pairs had a single long interval, they tended to have a long reproductive longevity. The findings suggest that rhythmicity of parturition intervals and, to a lesser degree, the physiological homeostatic ability are important in sustaining a long reproductive life and producing a large number of progeny during a life time. |
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