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U.S. Department of Agriculture3,4,, Clay Center, NE 68933-0166
Abstract
Experimental objectives were to measure the effect of ovulation rate on litter size at 86 d of gestation and at farrowing in 110 unilaterally hysterectomized-ovariectomized (UHO) gilts and in 142 intact, control gilts and to evaluate postnatal survival and development of progeny. Surgery (UHO) was performed on gilts 8 to 12 d following first estrus. Control and UHO gilts were mated and then randomly assigned to be slaughtered at d 86 of gestation or allowed to farrow. Gilts scheduled to farrow were observed by laparoscopy on d 40 of gestation to count corpora lutea (CL). Ovulation rate (number of CL) was similar for control (12.1 CL) and UHO (11.9 CL) gilts, thus indicating that compensatory ovarian hypertrophy had occurred in UHO gilts and resulted in a near doubling of ova per uterine horn relative to control gilts. Average litter size at 86 d of gestation and farrowing was greater (P<.01) for control than UHO gilts. At farrowing, litter size for control and UHO gilts was 9.0 ± .3 and 5.7 ± .3 pigs, respectively. Fetal losses were greater and pig weights at birth were less in litters by UHO gilts. Postnatal pig survival, growth rate to 14 d of age and 14-d individual pig weight did not differ for progeny of control and UHO gilts, and performance of UHO pogeny did not appear to compromise the usefulness of this animal model. Regression of litter size on ovulation rate was .41 ± .15 pigs/CL for UHO and .60 ± .12 pigs/CL for control gilts at d 86 of gestation. Regression was .07 ± .17 pigs/CL for UHO and .42 ± .14 pigs/CL for control gilts at farrowing. Averaged over time of evaluation, regression of litter size on ovulation rate was smaller (P<.05) in UHO gilts (.24 ± .12 pigs/CL) than in control gilts (.51 ± .10 pigs/CL). Litter size of UHO gilts at farrowing approached independence from ovulation rate, therefore the UHO procedure may allow estimation of uterine capacity per uterine horn unconfounded by ovulation rate.
1 Roman L. Hruska U.S. Meat Anim. Res. Center, P. O. Box 166, Clay Center, NE 68933-0166.
2 The cooperation of the Nebraska Agr. Exp. Sta., Univ. of Nebraska, Lincoln, is acknowledged.
3 Mention of a trade name, proprietary product or specific equipment does not constitute a guarantee or warranty by the USDA and does not imply approval to the exclusion of other products that may be suitable.
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