Identification of quantitative trait loci affecting reproduction in pigs

The objective of this research was to identify chromosomal regions harborin g QTL affecting reproduction in pigs. A three-generation resource populatio n was developed by crossing low-indexing pigs from a randomly selected cont rol line (C) with high-indexing pigs of a line selected for increased index of ovulation rate and embryonic survival (I). Differences between Lines I and C at Generation 10 were 6.7 ova and 3.3 fetuses at 50 d of gestation an d 3.1 fully formed and 1.6 live pigs at birth. Phenotypic data were collect ed on Fz females, born in three replicates, for ovulation rate (n = 423), a ge at puberty (n = 295), litter size (n = 370), and number of nipples (n = 428). Litter-size data included number of fully formed, live, stillborn, an d mummified pigs. Grandparent, F-1, and F-2 animals were genotyped for 151 microsatellite markers distributed across all 18 autosomes and the X chromo some. Genotypic data were available on 423 F-2 females. Averages pacing bet ween markers was 19.3 Kosambi centi-morgans. Calculations of logarithms of odds (LOD) scores were by least squares, and fixed effects for siredam comb ination and replicate were included in the models. Genome-wide significance level thresholds of 5% and 10% were calculated using a permutation approac h. There was evidence (P < 0.05) for QTL affecting ovulation rate on SSC9, age at puberty on SSC7 and SSC8, number of nipples on SSC8 and SSC11, numbe r of stillborn pigs on SSC5 and SSC13, and number of fully formed pigs on S SC11. There was evidence (P < 0.10) for additional QTL affecting age at pub erty on SSC7, SSC8, and SSC12, number born live on SSC11, and number of nip ples on SSC1, SSC6, and SSC7. Litter size is lowly heritable and sex-limite d. Therefore, accuracy of selection for litter size may be enhanced by mark er-assisted selection. Ovulation rate and age at puberty are laborious to m easure, and thus marker-assisted selection may provide a practical and effi cient method of selection.