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Influence of the Male's Presence on Sexual Maturation, Growth and Feed Efficiency of Female Mice^{1, 2,}

North Carolina State University, Raleigh 27607

Abstract

The influence of early mating of female mice on sexual maturation, fecundity, gain, feed intake and feed efficiency (gain/feed) was evaluated. Females were weaned at 3 weeks and randomly paired with a mature male at either 3 weeks (early-mated) or 7 weeks (late-mated), or maintained as virgin controls. Age at vaginal opening occurred significantly (P < .01) sooner in the early-mated group (26 vs 28 days) but at similar body weights (18.1 vs 18.4 g). Females that were larger at weaning tended to reach sexual maturity earlier. The correlation between weaning weight and age at copulatory plug was –.34 (P < .01) in the early-mated group. In addition, the regression of age at vaginal opening on weaning weight was –.90 ± .10 and –.93 ± .16 in the early- and late-mated groups, respectively. In late-mated females, age at vaginal opening was negatively related to early postweaning gain (b = –.84 ± .20), feed intake (–.53 ± .11) and feed efficiency (–.16 ± .06), whereas weight at vaginal opening was associated positively with these traits (.34 ± .10, .29 ± .05 and .05 ± .03, respectively). Early- and late-mated females differed markedly in age (29.2 vs 51.8 days) and weight (20.2 vs 24.5 g) at vaginal plug. However, early-mated females had an accelerated body weight gain so that by 16 days of gestation their mean weight was not significantly different from the late-mated group. The greater feed efficiency (gain/intake) of young females during gestation was due to their own efficiency and not to treatment differences in fetal efficiency. Body weights of early- and late-mated females were not different at about 3-weeks postpartum (10 and 13 weeks of age, respectively). However, early-mated females were 3.5 g heavier than virgin controls at 10 weeks while late-mated females were only 1 g heavier at 13 weeks.

¹ Paper No. 4436 of the Journal Series of the North Carolina Agricultural Experiment Station, Raleigh. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Experiment Station of the products named, nor criticism of similar ones not mentioned.

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

³ Department of Animal Science.