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Effects of Maternal Environment and Selection for Litter Size and Body Weight on Biomass and Feed Efficiency in Mice^{1 ,2,}

North Carolina State University, Raleigh 27650

Abstract

Five lines of mice differing markedly in litter size at birth and 6-week body weight were compared at several ages for litter size, biomass (litter size x mean individual body weight) and feed efficiency (biomass gain/feed intake). The lines were selected as follows: large litter size (L⁺), large 6-week body weight (W⁺), selection index to decrease litter size and increase 6-week body weight (L^-W⁺), selection index to increase litter size and decrease 6-week body weight (L⁺W^-) and random selection (K). In Exp. 1, females of each line were reared in postnatal litter sizes (PLS) of N8, N12 or N16 to determine the importance of this maternal environment on their subsequent reproductive performance. In Exp. 2, L⁺ and W⁺ females were reared in litters of eight. Litter size differences among lines (L⁺ > [W⁺,L⁺W^-] >K>L^-W⁺) and among PLS ([N8, N121] > N16) established at birth were maintained through weaning. At 12 days and 3 and 6 weeks, biomass of W⁺ females exceeded that of L⁺ females, and both lines had greater biomass than the controls. The two index lines exhibited negative correlated responses in biomass. The observed correlated responses in biomass at 6 weeks were compared to predicted values based on direct and correlated responses observed for litter size and 6-week body weight in each line. Observed and predicted responses were in reasonable agreement. The L⁺ and W⁺ lines did not show any correlated response in litter feed efficiency from birth to 12 days, whereas the index lines exhibited negative correlated responses. From 12 days to weaning, the line rankings in litter feed efficiency were W⁺>L⁺>K>L^-W⁺, while L⁺W^- was not different from K. Litter feed efficiency from conception to weaning had similar positive correlated responses in the W⁺ and L⁺ lines, while no improvement was found in the L⁺W^- and a decrease occurred in L^-W⁺. There was no important effect of either PLS or line x PLS interaction on biomass and litter feed efficiency.

¹ Paper No. 6066 of the Journal Series of the North Carolina Agr. Res. Service, Raleigh. The use of trade names in this publication does not imply endorsement by the North Carolina Agr. Res. Service of the products named, nor criticism of similar ones not mentioned.

² The technical assistance of Ms. Billie Jean Edwards is acknowledged.

³ Dept. of Anim. Sci.

⁴ Present address: Zoological Soc. of San Diego, San Diego, CA 92112.

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