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Journal of Animal Science, Vol 71, Issue 3 608-617, Copyright © 1993 by American Society of Animal Science

JOURNAL ARTICLE

Changes in ovulation rate, uterine capacity, uterine dimensions, and parity effects with selection for litter size in swine

L. L. Gama and R. K. Johnson
Department of Animal Science, University of Nebraska, Lincoln 68583-0908.

This study was conducted with random samples of pigs of a line (LS) selected for eight generations for litter size and a randomly selected control line (RS) in the Nebraska Gene Pool population and of crosses of these lines with a Large White-Landrace composite line (I) that was selected for an index of ovulation rate and embryonic survival to 50 d of gestation. Two experiments were done to obtain information on ovulation rate, uterine dimensions, and uterine capacity. In Exp. 1, 103 gilts were slaughtered 9 to 16 d after their second estrus to obtain reproductive tracts for evaluation of ovulation rate and uterine dimensions. In Exp. 2, unilateral hysterectomy-ovariectomy was performed 3 to 10 d after puberty in 109 gilts that were then mated at their next estrus and slaughtered at 93 to 100 d of gestation to recover reproductive tracts for evaluation. Litter size at birth was recorded at first (n = 414), second (n = 159), and third (n = 143) parity of pureline and crossline gilts. The cumulative response to eight generations of selection for litter size pooled over type of cross and parity was 1.21 +/- .38 pigs, in good agreement with the realized response of 1.06 pigs previously estimated for the period of selection. This response was due to an increase of 1.30 +/- .54 eggs in ovulation rate (measured by the number of corpora lutea in cyclic and pregnant gilts) and .66 +/- 1.28 pigs in uterine capacity (measured after unilateral hysterectomy-ovariectomy). No significant changes were found in uterine dimensions in cyclic gilts. Approximately 25% of the increase in litter size could be explained by a reduction in number of mummified pigs at birth, an indication that uterine capacity in late gestation was increased. Estimated differences between lines (gLS - gRS) were not significantly different for pureline and crossline gilts and sows, and no interactions of these estimates with parity were detected. Estimates of heterosis for LS x I and RS x I did not differ significantly, nor were interactions of heterosis with parity significant.


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Copyright © 1993 by the American Society of Animal Science.