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Prenatal and Postnatal Effects in Mouse Lines Selected for Body Weight and Litter Size: Performance of Postnatal Dams and Growth of Progeny^1,2,

North Carolina State University, Raleigh 27695-7621

Abstract

A crossfostering experiment that included litter size standardizations of 8 (LS8) and 16 (LS16) was performed to determine line differences in postpartum maternal performance of dams and prenatal and postnatal effects on growth of young. Lines evaluated were: W, selected for increased 6-wk body weight; L, selected for increased litter size at birth; LW, selected for increased litter size and decreased 6-wk body weight and K, selected at random. Line differences in feed consumption of lactating dams paralleled those in body weight (W > L > K > LW). For litter efficiency [litter weight gain/dam feed consumption] to 12 d postpartum (pp), increasing litter size affected only LW; litter efficiency decreased at LS16. Line rank at LS8 was L > W > LW, but neither L nor W differed from K; whereas at LSI6 the rank was (L, W, K) > LW. There were no line differences in litter efficiency from 12 to 21 d pp. Line differences in mortality within litters were observed only at LS16 and were not dependent on the genotype of the pups. Rank of lines for mortality to 12 d pp was LW > K > (L, W). From 12 to 21 d pp, all selected lines had lower mortality rates than K, but correlated responses were significant only in L and W. Generally, the rank for prenatal effects on individual body weights at 12, 21 and 42 d was W > L > K > LW. For postnatal effects the rank was (W, L) > K > LW. Interactions of LS with pre- or postnatal effects and between pre- and postnatal effects were biologically unimportant. Through 21 d, LS16 tended to depress prenatal effects but had less influence on postnatal effects. While postnatal effects decreased with age, and prenatal effects increased, the time schedule and relative degree of these changes varied with line. At the litter size at which the lines had been selected (LS8), prenatal effects usually accounted for more of the positive response for weight in W, whereas postnatal effects were the reason for decreased weight in LW.

¹ Paper No. 8986 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the products named, nor criticism of similar ones not mentioned.

² The authors are thankful for the technical assistance of Mses. J. Sherrod and C. Powers.

³ Present address: Dept. of Anim. Sci., Purdue Univ., Lafayette, IN 47907.

⁴ Dept. of Anim. Sci.

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