J. Anim Sci.
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J. Anim Sci. 1975. 40:590-597.
© 1975 American Society of Animal Science
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Selection Index Based on the Nursing Ability of the Mother and the Mature Weight of the Offspring in Mice1

Jiro Nagai, C. G. Hickman and G. R. Barr2

Animal Research Institute, Agriculture Canada, Ottawa, K1A 0C6

Abstract

Data from two mouse populations of different origin (P and Q) were analyzed to estimate genetic parameters for the nursing ability of the mother (m) and the body weight of the offspring at 42 days of age (w), and to develop a selection index based on m and w. The nursing ability of the mother was measured by the mean individual 12-day weight of a nursed litter. At birth, the young were exchanged among mothers so that each nursed litter contained eight young representing four mothers. For the line (M) selected for m, the line (W) selected for w, the line (B) selected for an index combining m and w, and the unselected line (C), heritability estimates of m from daughter-dam regressions pooled over three generations were .37, .27, .29 and .33 in P, and .25, .10, .17 and .04 in Q, respectively. For W, B and C, heritabilities of w estimated by doubling the litter (prenatal) component of variance within crossfostering groups were .20, .33 and .26 in P and .28, .36 and .34 in Q. Genetic correlations between m and w estimated from the marginal totals of crossfostering groups for W, B and C were .24, .99 and .37 in P and –.25, .07 and .29 in Q, respectively. In the index where equal economic weights were assumed for M and W, the coefficients in P and Q were .33 and .14 form and .53 and .38 for w. This indicated that when selecting for both m and w, more emphasis was placed on the performance of w than on the performance of m, and that m could be genetically improved through selection of w alone as indicated by the genetic correlation between m and w. It was found that the expected responses to selection based on the index were larger in w than in m, and the expected response for m relative to that for w was larger in P than in Q.

Footnotes

1 Contribution No. 535 Animal Research Institute, Research Branch, Agriculture Canada, Ottawa, Ontario, K1A 0C6.

2 The authors wish to express their appreciation to Drs. B.1 B. Bohren and Alan Emsley for their valuable comments on the manuscript.






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Copyright © 1975 by the American Society of Animal Science.