Identification of quantitative trait loci affecting reproduction in pigs

The objective of this research was to identify chromosomal regions containing QTL affecting reproduction in pigs. A three-generation resource population was developed by crossing low indexing animals from a randomly selected control line (C) with high indexing animals of a line selected for increased index of ovulation rate and embryonic survival (1). Differences between Lines I and C at Generation 10 of selection were 6.7 ova and 3.3 fetuses at 50 d of gestation and 3.1 fully formed and 1.6 live pigs at birth. Phenotypic data were collected in F2 females for ovulation rate (n = 423), age at puberty (n 295), litter-size (n = 362) and number of nipples (n = 423). Litter-size data included number of fully formed, live, stillborn, and mummified pigs. Grandparent, F1, and F2 animals were genotyped for 151 microsatellite markers distributed across all 18 autosomes and the X chromosome. Genotypic data was available on 423 F2 females. Average spacing between markers was 19.3 Kosambi centimorgans. Calculations of LOD scores were by least squares including fixed effects of sire-dam combination and replicate. Genome-wide significance level thresholds of 5% and 10% were calculated using an empirical permutation approach. There was evidence at the 5% significance level for QTL affecting ovulation rate on Chromosome 9, age at puberty on Chromosomes 7 and 8, number of nipples on Chromosomes 8 and 11, number of stillborn pigs on Chromosomes 5 and 13, and number of fully formed pigs on Chromosome 11. At the 10% significance level there was evidence of additional QTL affecting age at puberty on Chromosomes 7,8, and 12, number born live on Chromosome 11, and number of nipples on Chromosomes 1, 6, 7, and 8. Ovulation rate and litter traits are lowly to moderately heritable and sex limited. Therefore, response to selection for these traits might be enhanced by marker-assisted selection (MAS). Ovulation rate and age at puberty are labor intensive to measure and thus, may benefit most from marker-assisted selection