Plant & Animal Genome VI Conference

W61

ANALYSIS OF NEW CANDIDATE GENES FOR REPRODUCTION IN THE PIG

Department of Animal Science, Iowa State University, Ames, IA 50011-3150

Litter size is one of the most economically important traits of interest to swine producers. Because of its low heritability (.10), litter size has not responded well to conventional selection approaches. Beginning in 1991, we began a major effort to investigate the role of candidate genes in controlling litter size. Our first gene, Estrogen Receptor (ESR), has now been shown to have a major effect on litter size. Results from Chinese pig crosses demonstrated a 2.3 pig advantage between homozygotes for first parity. In commercial Large White crosses, analyzing 4,262 first parity records has shown that differences between homozygotes are over .8 pigs/litter with no negative effects on other traits. More recent studies now include Retinoic Acid Receptor Gamma (RARG), Retinol Binding Protein 4 (RBP4), Melatonin Receptor 1A (MTNR1A) and the Prolactin Receptor (PRLR). The most promising of these genes is the PRLR. Analysis of six commercial lines involving Meishan, Large White, Landrace, Pietrain and Duroc origin have shown that the A-allele is significantly associated with increased litter size in four of them. Effects of the A-allele in these four lines range from .6 to over 1 pig per litter difference between homozygotes. Further validation work is needed to confirm these results, but this PRLR gene test has the potential to be another powerful tool to improve litter size. The financial support for this research was provided in part by PIC and is gratefully acknowledged.