FACTORS AFFECTING THE SURVIVAL AND GROWTH OF YOUNG MICE BORN AND REARED AT 36°

Summary About 90% of the pups born to mothers gestating and lactating at 36° died during the first 24 hr. of extra‐uterine life. Maternal failure accounted for approximately 50% of these losses, and poor pup viability for about 25% of pup deaths. Maternal failure appeared to be due to several factors: to failure to secrete milk in the pre‐natal period, to an increase in the time between the birth of the litter and the first feed or to a reduction in the amount of milk produced during the first 24 hr. after parturition. Transfer of mothers from 21° to 36° on the day of parturition led to the death of all pups. When transfer to 36° was delayed until 4 days after parturition, 83% of the mothers were alile to rear a litter, in whole or in part, to 21 days. The weaning weights of pups reared by mothers gestating at 21° and lactating at 36° were similar to those of pups reared by mothers gestating and lactating at 36°. The weaning weights of pups reared by mothers gestating at 36° and lactating at 21° were similar to those of pups reared by mothers Restating and lactating at 21°. There was a significant difference between the weaning weights of pups reared at 21° and those reared at 36°.