Effects of reduction of litter size on subsequent growth and reproductive performance in mice

Abstract

SUMMARYLitters that contained at least 13 mice were reduced at birth to 12, 8, or 4; and any natural litters of these sizes were also kept. The growth of these mice and their subsequent reproductive performance when mated at 6,10 and 14 weeks of age were recorded. All their offspring were weighed at weaning (4 weeks); some were weighed also at 12 days and 6 weeks of age.The amount of milk supplied was not fully adjusted to the size of the litters. This had lasting effects so that, even at the oldest age for mating, the mice from the small litters were noticeably the heaviest. Litter size effects extended to significant differences in fertility (numbers born) and less obviously to the numbers weaned. The mice that were mated at 14 weeks were the most fertile. There was little to distinguish the mice from natural and reduced litters of the same size.Small differences in weights of the offspring at 12 days, 4 weeks and 6 weeks of age bore no consistent relation to these factors.