P O S T N a T a L L Itter Size Effects on Growth a N D R E P R O D U C T I O N in Rats 1

The effects of postnatal litter size on preand postweaning growth, daughter 's litter size and rebreeding performance of the dam were examined in rats that had undergone 14 generations of selection for rate (LG) or efficiency (LE) of postweaning protein gain followed by relaxed selection, and in a randomly selected control line (C). Data came from generations 23 to 24 (standardized litters) and 25 to 26 (unstandardized litters). Generation 25 dams were remated at weaning for two addit ional parities. Regressions of average pup weight on average postnatal litter size were negative and increased in magnitude from birth to weaning, but decreased with parity number. Average litter size from birth to weaning (3 wk) affected postweaning weights at 5 and 7 wk, but compensatory growth occurred, especially during wk 3 to 5. The effect of dam's litter size (the litter in which the daughter was born) on daughter 's weight was still negative and significant at mating and affected litter size of daughters. This negative maternal effect on daughter 's litter size was larger when the dam's litter was not standardized. Litter size weaned also affected rebreeding interval of females. (