EVIDENCE FOR QUANTITATIVE TRAIT LOCI AFFECTING OVULATION RATE IN PIGS

Fifty-five microsatellite markers were scored in an F-2 population of pigs (n = 114 females) developed at the University of Nebraska. The po pulation was produced by crossing a line previously selected for 10 ge nerations using an index of ovulation rate and embryonal survival and a line selected at random. The lines were from a common base populatio n and differed by 6.7 ovulations and 3.1 fetuses at 50 d of gestation. Ovulation rate and number of fully formed and mummified pigs were rec orded for each female. Data were analyzed with regression models that included random animal effects. Likelihood-ratio tests were used to te st for quantitative trait loci (QTL) effects by deviating the log-like lihood for the full model that included additive and dominance QTL eff ects from the log-likelihood for the reduced model that did not contai n QTL effects. A QTL for ovulation rate was found on chromosome 8 (P < .001) with an additive effect of 3.07 ovulations. Other evidence of po tential QTL affecting ovulation rate was found on chromosomes 4 (P <.1 0), 13, and 15 (P <.05). Effects on chromosomes 4, 13, and 15 were not significant for an experiment-wise threshold value of P <.001. No sig nificant QTL for litter size or number of mummified pigs were found. A dditional data are needed to confirm the location and the effect of QT L found for ovulation rate before markers associated with them can be used in marker-assisted selection.