The effect of litter size on the growth, survival and behaviour of neonatal bulbectomised mice.

Bilateral lesions of the olfactory bulbs in 1-day-old mice led to a slow rate of growth both before and after weaning and the growth changes were positively associated with the size of the lesion. Mothers continued to care for the bulbectomised mice which showed no evidence of retarded motor development though their eyes opened later and they were less active when exposed to an artificial perfume. Bulbectomised mice failed to survive in litters of two where both infants were bulbectomised and in litters with a large number of unoperated littermates. Keeping litters small and having both bulbectomised and control mice present enhanced the chances of survival and the presence of infant control mice is a necessary condition for the maintenance of lactation and the survival of the bulbectomised babies. Failure to respond to the odours( pheromones) of the mothers may be responsible for the infrequent suckling and the slow growth and development.