Initial results of genomic scans for ovulation rate in a cattle populationselected for increased twinning rate

Genomic scans were conducted with 273 markers on 181 sires from a cattle po pulation selected for increased twinning rate to identify chromosomal regio ns containing genes that influence ovulation rate. Criteria used for select ing markers were number of alleles, ease of scoring, and relative position within linkage group. Markers were multiplexed or multiple-loaded on the ge ls to reduce the costs and labor required to obtain genotypic data. This ap proach reduced the number of gels by 45% when compared with running each ma rker independently Male animals selected for the genomic scan sired the maj ority of the population. A modified interval analysis was used in a grandda ughter design to compare effects of each allele within sire for 10 differen t sire families. The midparent deviation of the son's estimated breeding va lue for ovulation rate was used as the phenotype. Forty-one potential peaks were identified with a nominal significance level less than or equal to0.0 5. The 10 peaks with the highest significance levels (P < 0.02) were select ed for further analysis. Markers were genotyped across daughters of the sir e where nominal significance was found for each of the 10 peaks. One peak ( BTA5, relative position 40 cM) was found to be nominally significant in the daughters. The nominal significance levels were P = 0.01 for the sons (n = 32) and P = 0.02 for the daughters in = 94) of sire 784403. A combined gen omewide significance value (P = 0.07) was calculated that accounted for the 10 analyses with sons and the 10 analyses with daughters. These results st rongly suggest that this region contains a gene(s) that is involved in the follicular recruitment and development process.