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Selection for Ovulation Rate in Swine: Correlated Response in Litter Size and Weight¹

University of Nebraska, Lincoln 68583^4,5,

Abstract

Nine generations of direct selection for ovulation rate (OR) were evaluated to determine the magnitude of the correlated response in three litter size and two litter weight traits. A total of 387 Select line and 394 Control line litters were included in the ten generations of data. Realized heritability of OR was .42 ± .06 based on the regression of response (Select-Control) on weighted cumulative selection differential.

Regressions of line means on generation number were significant for litter birth weight in both lines (–.31 ± .12 kg, Select; –.41 ± .06 kg, Control) and for litter weaning weight (–3.4 ± .8 kg) in the Control line. None of the other regressions of line means on generation number was significantly different from zero. Regressions of line difference (Select-Control) on generation number were .06 ± .07, .07 ± .07, .10 ± .07, .10 ± .10 kg and 1.2 ± .8 kg for total number farrowed (TNF), number farrowed alive (NFA), number weaned (NW), litter birth weight (LBW), and litter weaning weight (LWW), respectively. However, none of these estimates of correlated response was significantly different from zero.

Estimates of realized genetic correlation obtained were .07 (OR-TNF), .11 (OR-NFA), .24 (OR-NW), .18 (OR-LBW) and .20 (OR-LWW). Although positive, none of the estimates approached statistical significance indicating that direct selection for ovulation rate would be expected to have little genetic effect on litter productivity. The failure to obtain significant correlated responses in litter size was suggestive of a decline in fertilization rate and/or embryonic survival since ovulation rate has been increased by selection.

¹ Published with the approval of the Director as Paper No. 5542, Journal Series, Nebraska Agr. Exp. Sta. Research reported was conducted under Project 13-1.

² Present address: University of Nebraska, North Platte Station, North Platte.

³ Present address: USMARC, Clay Center, NE.

⁴ Department of Animal Science. The authors wish to express their sincere appreciation to the unit managers and other employees for their diligence in the collection of the data used in this study.

⁵ This research was supported in part by a cooperative agreement with the Agricultural Research Service, USDA.

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