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Selection for Postweaning Gain in Rats: II. Correlated Response in Reproductive Performance¹

University of Nebraska and U.S. Department of Agriculture, Lincoln 68583-0908

Abstract

Reproductive performance was evaluated on lines of rats selected 34 generations for up (U) and down (D) 3- to 9-wk weight gain and from a control (C). Direct response to 3- to 9-wk weight gain was 16% in U and –8% in D lines. Inbreeding was similar among lines. Both selection lines were poorer in percentage of fertile pairs than the C line, especially so in D (P<.10). The lines differed (P<.05) in litter size born with means of 11.4, 10.4 and 9.6 for U, C and D, respectively. The significant positive correlated response in litter size corresponded to that expected from intraline association with female body weight. Selection for increased postweaning gain resulted in 5% earlier age but little change in weight at vaginal opening. The D line was similar to C in age, but 7% lighter in weight at vaginal opening. The U line was significantly higher (14, 12 and 69%) for ovulation rate, number of fetuses and post-implantation losses, but not for pre-implantation losses. The D females were similar to C females in all components of litter size. Males of all lines were similar in age at first mating, but U males were 22% heavier than C males in weight at first mating. A positive correlated response in weight of testes at 91 d of age disappeared when adjusted for intraline association with body weight.

¹ Published as Paper No. 7879, Journal Ser., Nebraska Agr. Exp. Sta., Lincoln. Appreciation is expressed to A. B. Chapman and J. J. Rutledge, Univ. of Wisconsin, Madison, for providing the genetic stocks used in this study.

² Present address: Facultad de Zootecnia, Univ. of Chihuahua, Chihuahua, Mexico.

³ Anim. Sci. Dept., Univ. of Nebraska, Lincoln, 68583-0908.

⁴ Roman L. Hruska U.S. Meat Anim. Res. Center, ARS, USDA, 225 Baker Hall, Univ. of Nebraska, Lincoln 68583-0908.