Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2004
Publication Date: 3/1/2005
Citation: Snowder, G.D., Cushman, R.A., Allan, M.F., Thallman, R.M., Echternkamp, S.E. 2005. Heritability estimate for bilateral ovulation in heifers [abstract]. Midwestern Section of the American Society of Animal Science 83(2):39. Interpretive Summary: No interpretive summary is required.
Technical Abstract: Recent studies have reported that cows giving birth to twin calves as a result of bilateral ovulations have lower incidences of dystocia and higher calf survival than twins born from the same uterine horn. Therefore, the objective of this study was to determine if bilateral ovulation in heifers is genetically influenced. The data set included multiple ovarian palpation records from a total of 3,910 heifers born from 1984 to 2002. The average number of estrous cycles per heifer was 7.5 times (total records = 29,548). Heifers were from a MARC herd selected for increased calving rate. Over the time span of this project, selection has increased total ovulation rate at an annual rate of 0.026. Bilateral ovulation was defined as a binomial trait within double ovulation records (1 = bilateral and 2 = unilateral; total records = 5,780). Ovulation rate was defined as the total number of corpora lutea per estrous cycle. Heritability and covariance components for bilateral ovulation and ovulation rate were estimated using a two-trait repeated measures animal model. Because the herd population was a composite of 11 different breeds, breed composition fractions for each heifer were considered as covariates. Linear and quadratic forms of age of heifer at palpation were also included as covariates. Year and season of birth subclass code was considered a fixed effect. The heritability estimate for bilateral ovulation was low (0.02 ± 0.01), as is common for most reproductive traits. The heritability estimate for ovulation rate was also low (0.09 ± 0.01) consistent with previous estimates. The estimated genetic correlation between bilateral ovulation and ovulation rate was 0.72. Selection response for bilateral ovulation in heifers will be slow. Cumulative advantages of selecting for bilateral ovulation in heifers may be determined by future studies that estimate the genetic relationships of heifer bilateral ovulation with calving rate, cow longevity, dystocia incidence, and calf survival.