Genetic Trends for Reproductive Traits in Duroc Swine
Tom J. Baas1, John W. Mabry1, Steven J. Moeller2, Kenneth J. Stalder3, and Miles T. See4
1Department of Animal Science, Iowa State University, Ames, IA 50011;
2Department of Animal Sciences, The Ohio State University, Columbus, OH 43210;
3Department of Animal Science, The University of Tennessee, Jackson, TN 38305;
4Department of Animal Science, North Carolina State University, Raleigh, NC 27695
Best Linear Unbiased Prediction (BLUP) genetic evaluation procedures are used in the swine industry to produce breeding value (BV) estimates for seedstock replacements that can be used in making selection decisions. BV estimates rank animals according to their genetic merit as parents, thus identifying genetically superior seedstock for traits of interest. Evaluation of BV genetic trends over time provides an indication of selection emphasis and rate of genetic improvement in a breed or population.
Materials and Methods
Genetic trends in the U.S. population of purebred Duroc swine were evaluated using data from participating breeders over an 11-year period from 1988-1998. The PEST genetic evaluation software was used to produce BV estimates. Genetic trends were estimated based on the average BV for all animals born during a specific year. The model used to estimate BVs for the reproductive traits of number born alive (NBA), number weaned (NW), and 21-day litter weight (LWT) included the fixed effect of contemporary group (CG) and the random effect of the genetic effect of the animal. Permanent environment and mate within CG were included as uncorrelated random effects. CG was determined by the breeder and was defined as a group of females that were bred, gestated, farrowed, and weaned together under similar environmental conditions. Data were preadjusted using breed-specific adjustment factors for known sources of variation as described in (1). NBA was adjusted for parity, age at farrowing, number allowed to nurse, and age at weighing. Components of (co)variance used for BV estimation were specific to the Duroc breed as described in (2). Four postweaning traits were evaluated: days to 114 kg (DAYS); backfat at 114 kg (BF); loin muscle area at 114 kg (LMA); and kg of lean in a 84 kg carcass (LEAN). BVs for these traits were estimated with a model that included fixed effects of CG and sex within herd, the genetic effect of the pig as a random effect, and the litter in which the pig was born as an uncorrelated random effect. CG was a group of pigs that was farrowed, housed, and fed together. All postweaning data were adjusted to 114 kg using procedures described in (2). Maternal Line Index (MLI), a multi-trait bio-economic index combining NBA, NW, LWT, DAYS, BF, and LEAN, was computed.
Results and Discussion
Genetic trends from 1988-1998 indicate significant progress in NBA, LWT, and MLI in the Duroc breed, with most of the improvement occurring since 1992. Genetic improvement for this period for NBA, LWT, and MLI was 0.028 pigs/year, 0.083 kg/year, and 1.02 index units/year, respectively. Significant improvement in DAYS (-0.327 days/year), BF (-0.411 mm/year), LMA (0.357 sq cm/year), and LEAN (0.148 kg/year) was also realized. Selection emphasis on postweaning traits over an 11-year period did not inhibit genetic progress in reproductive traits in the Duroc population.
(1) Culbertson, M. S., J. W. Mabry, J. K. Bertrand, and A. H. Nelson. 1998. Breed specific adjustment factors for reproductive traits in Duroc, Hampshire, Landrace, and Yorkshire swine. J. Anim. Sci. 75:2362-2367.
(2) (2) Mabry, J. W. 1998. The new STAGES program: How will the numbers change. Seedstock Edge 5:45-49 (No. 4).
Previously published in the proceedings of the 14th International Congress on Animal Reproduction (ICAR), Vol 1:P 304. July, 2000. Stockholm, Sweden