Difference in reproductivity and offspring growth between litter numbers in four strains of mice.

As a means to improve mouse production, the differences among litter numbers in reproductivity, post-weaned growth and puberty of offspring were examined in 4 strains of mice, SHN/Mei, SLN/Mei, C3H/HeMei and GRS/AMei. Females were mated to be concurrently pregnant and lactating and reproductivity was recorded from the 1st to the 3rd litters. Some offspring of both sexes were weighed at 30, 40 and 50 days of age and vaginal opening was also checked in females. Pre-weaned growth of offspring differed little between litter numbers in all strains except GRS/A. Meanwhile, post-weaned growth of offspring was higher in the 2nd and 3rd litters than in the 1st litter of SHN and SLN, associated with a decreased rate of still-born pups. In C3H/He, post-weaned growth of offspring was higher in the 1st and 2nd litters and rearing rate decreased for the 3rd litter. In GRS/A, the 1st litter showed the greatest pre- and post-weaning growth rate of offspring. All findings indicate that in SHN and SLN strains the later litters are better for offspring production, while in C3H/He and GRS/A strains it is the earlier litters. The results stress the value of having information on reproductive characteristics of mouse strains for efficient offspring production.