Submitted to: Animal Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 7, 1996
Publication Date: N/A
Interpretive Summary: There is genetic variation in ovulation rate in cattle. Ovulation rate has been shown to be a useful indirect selection criterion for twinning rate. If present, Quantitative Trait Loci (QTLs) for ovulation rate could be used to increase rate of improvement of twinning rate in cattle. Genetic markers for ovulation rate QTLs were detected on chromosomes 7 and 23 in the daughter progeny of two sire families in which ovulation rate was determined. The marker on chromosome was associated with an effect in excess of one phenotypic standard deviation and accounted for 10% of the phenotypic variation in ovulation rate. The marker on chromosome 23 in a second sire family was associated with an effect of slightly less than half a phenotypic standard deviation and accounted for 4% of the phenotypic variation in ovulation rate.
Genetic variation in ovulation rate is known to exist in cattle. Seventy- seven polymorphic microsatellites were analyzed in offspring of three elite sires that were part of the foundation of an experimental population selected for twinning rate at the Roman L. Hruska U.S. Meat Animal Research Center. All females were assessed for ovulation rate by rectal palpation of corpora lutea over 8-10 consecutive estrous cycles from approximately 1 to 18 mo of age, and associations between ovulation rate and sire allele were examined in each of the three sire groups. A preliminary analysis was performed using selectively genotyped daughters of each sire. Markers found significant or approaching significance, were also genotyped in all daughters, sons and granddaughters of these sires. A test of marker association limited to the granddaughter data provided an independent confirmation of marker effect and significance relative to the initial test twith daughter data. Putative ovulation rate QTL's were detected on chromosomes 7 and 23. Marker UWCA20 on chromosome 7 was associated with an effect in excess of one phenotypic standard deviation and accounted for approximately 10% of phenotypic variation in ovulation rate. Marker CYP21 (steroid 21-hydroxylase) on chromosome 23 was associated with an effect of slightly less than half of a phenotypic standard deviation and accounted for approximately 4% of phenotypic variation. The significance of markers nearby these purative QTLs aided in validating these results.