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The effect of increased growth rate during the suckling period on subsequent body growth rate and muscle weight to body weight (MW/BW) ratio was examined in inbred and outbred male and female mice. Growth rate during the suckling period was increased by reducing litter size to 4 pups within six hours of birth. Body weight, MW/BW ratio, and dry weight to wet weight (DW/WW) ratio for the soleus, tibialis anterior, extensor digitorum longus, biceps brachii, and heart muscles were measured at 4, 8, 16, and 24 weeks of age. The results indicate that increasing growth rate during the suckling period results in an increased body weight at 24 weeks of age in outbred male and female mice; whereas, in inbred male and female mice body weight is greater at 4 weeks of age but by 8 weeks of age the mice raised in normal litters have "caught up" with those raised in small litters. MW/BW ratio is increased in several muscles during the suckling period but returns to normal during the post weaning period.