Submitted to: Animal Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/28/2011
Publication Date: 4/1/2012
Citation: Mousel, M.R., Leymaster, K.A., Christenson, R.K., Nonneman, D.J., Rohrer, G.A. 2012. Validation and fine mapping of a QTL for ovulation rate on swine chromosome 3. Animal Genetics. 43(2):220-224.
Interpretive Summary: Ovulation rate is an important component of litter size yet causative mutations or genetic markers have been identified in pigs. Markers within a QTL region on chromosome 3 were tested in three white composite lines selected for 10 generations for increased ovulation rate, uterine capacity or an unselected control. Selection increased ovulation rate 3.2 eggs in the ovulation rate selected line compared to the control and uterine capacity selected lines. Six microsatellites and 10 single nucleotide polymorphisms (SNP), which spanned from the QTL region, were genotyped in pigs from all lines in generations 11 through 13. Significant changes in allele frequencies were found in the ovulation rate selected line compared to the control line. In addition, a significant association of one genetic marker with ovulation rate was detected along with additional marker associations approaching significance. The estimated effects on ovulation rate were approximately 0.6 additional eggs ovulated for each copy of the desirable allele. Current results suggest there may be two genes affecting ovulation rate in this region. This study has validated the ovulation rate QTL previously identified. Further evaluations of this region in other populations need to be conducted to resolve the number of genes affecting ovulation rate and develop markers for use in industry populations.
Technical Abstract: Ovulation rate (OR) is an important component of litter size. The causative mutation(s) in gene(s) underlying OR QTLs have yet to be identified in pigs. Markers within an OR QTL on SSC3 were genotyped in three white composite lines selected for 10 generations for increased OR, uterine capacity (UC) or an unselected control. A realized increase of 3.2 corpora lutea (CL) was observed in the ovulation rate selected line compared to the control and uterine capacity selected lines. Number of CL and UC (number of fully-formed fetuses) were collected at approximately 105 days of gestation as well as ovary weight (OW), uterine length (UL) and uterine weight (UW) measurements at 160 d of age in generations 12 and 13 of females from all three lines. Six microsatellites and 10 single nucleotide polymorphisms (SNP), which spanned from 0 cM to 42 cM, were genotyped in pigs from all lines in generations 11 through 13. Allele frequencies of 24269.1, SW2429, 7907.2 and 7637.2 were different (P < 0.01) in the ovulation rate selected line compared to the control line. A significant (P < 0.05) association of CL with 24269.1 (additive effect 0.65+0.32) was detected and additive genotypic effects approached significance for markers at 28 through 35 cM (16963.2, 27514.1 and SWR1637) of SSC3. Haplotyping of 7637.2 and 16963.2 (31 through 32 cM) identified a significant additive association of haplotype 1 with CL (-0.62+0.30). In addition to associations with CL, these markers were associated with OW (24296.1 and SWR1637), UL (16963.2, 27514.1 and haplotypes of 7637.2/16963.2) and UW (haplotypes of 7637.2/16963.2). This study verifies an OR QTL on SSC3; however, these data indicate there may be two genes, at 0 through 18 cM and 28 through 35 cM, controlling OR in this region.