Reproductive Trait Genetic Trends In American Landrace Swine


K.J. Stalder1*, J.W. Mabry2, J. Venner3, T. J. Baas2, S. J. Moeller4, and M.T. See5

1University of Tennessee, Knoxville,

2Iowa State University, Ames,

3National Swine Registry, West Lafayette, IN,

4Ohio State University, Columbus, and

5North Carolina State University, Raleigh U.S.A.



Maternal performance of the breeding herd greatly impacts the profitability of commercial and seedstock swine producers. The traits generally considered to be the most economically important include: number born alive (NBA), litter birth weight, number of pigs weaned (NWN), 21-d litter weight (LWT) and litters per sow per year. Though generally considered lowly heritable, genetic improvement of reproductive traits can be successful because of recent implementation of best linear unbiased prediction (BLUP) statistical methodologies. Hence, genetic improvement of swine reproductive traits can improve the profitability of swine production.


Materials and Methods

American Landrace breeders have conducted across herd genetic evaluations of their animals since 1988.  Breeding values (BV) for NBA, NWN and LWT were estimated using an animal model that includes contemporary group (CG) as a fixed effect and genetic effect of the animal as a random effect. Permanent environment and mate within CG were included as uncorrelated random effects. Contemporary groups were defined as a group of sows that were bred, gestated, farrowed and weaned together and were designated by the breeders. Data were pre-adjusted for known sources of variation as described in (1). NBA was adjusted for parity of sow and age at farrowing. NWN was adjusted for the number of pigs allowed to nurse and is therefore, a measure of pre-weaning mortality. LWT was adjusted for parity of sow, age at farrowing, number of pigs nursed and age of litter at weaning. Components of (co) variance used for breeding value estimation were specific for the American Landrace breed as described in (2). Breeding values for post-weaning traits of days to (DAYS), backfat (BF) and loin muscle area (LMA) and kg of lean in an 84kg carcass were estimated using a model that included CG and sex within herd as fixed effects. The genetic effect of the pig was used as a random effect, while an uncorrelated random effect for the pig’s birth litter was included in the analysis model. Breeders defined CG as a group of pigs that were housed and fed together. All post-weaning data were adjusted to 114kg as described in (2). Genetic trends were estimated by averaging the BV of animals born within a specific year for each trait.


Results and Discussion

Eleven years (1988-1998) of reproductive trait data collection has allowed for BV genetic trends to be estimated over a long period of time. Since 1988, the average BV for NBA, NWN and LWT has improved .33 pigs, .037 pigs and 1.11kg, respectively. Yearly genetic improvement for NBA, NWN and LWT has averaged .03 pigs, .003 pigs and .1kg, respectively. American Landrace breeders have made significant genetic improvement for economically important reproductive traits by implementing effective selection programs. Genetic improvement should help breeders and their commercial clientele improve the profitability of their pork operations.



(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)   Mabry, J.W. 1998. The new STAGES program: How will the numbers change? Seedstock Edge 5:45-49 (no.4). West Lafayette, IN U.S.A.


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Originally presented at the 14th International Congress on Animal Reproduction, Stockholm, Sweden, 2-6 July, 2000 and

 published in the Proceeding of the 14th International Congress on Animal Reproduction Volume 1 page 305.

2000 NSIF Proceedings