Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2006
Publication Date: 6/1/2006
Citation: Macneil, M.D., Geary, T.W., Perry, G.W., Roberts, A.J., Alexander, L.J. 2006. Genetic partitioning of variation in ovulatory follicle size and probability of pregnancy. Journal of Animal Science 84:1646-1650. Interpretive Summary: Sustained reproductive success is the most important determinant of efficient and profitable beef production. However, a lack of identified highly heritable traits that are closely correlated with fertility limits opportunity for genetic improvement of efficiency and profitability. Previous research has identified size of the ovulatory follicle as being temporally associated with the conception and/or establishment of pregnancy. However, there has been no previous attempt to estimate the degree to which genetic effects control neither variation in follicle size nor the magnitude of its relationship with pregnancy rate. Thus, objectives of this work were to estimate heritability of follicle size and to assess its usefulness as an indicator trait associated with reproductive success in beef cattle. Data were collected during the years 2002 to 2005 from 780 beef females that ranged in age from 1 to 12 yr. There were on average 2.4 observations per female. Results indicate heritability of size of the ovulatory follicle is greater than the heritability pregnancy rate. However, owing to a very low genetic correlation of follicle size with pregnancy rate its greatest usefulness in genetic selection is as an ancillary trait. This research is of greatest value in the continued exploration of the biological basis for sustained successful reproduction.
Technical Abstract: Objectives of this research were to partition variation in ovulatory follicle size into genetic and non-genetic components and to assess the utility of ovulatory follicle size as an indicator trait associated with reproductive success in beef cattle. Data were collected during the years 2002 to 2005 from 780 beef females that ranged in age from 1 to 12 yr. There were on average 2.4 observations per female. Data were analyzed with a multiple trait Gibbs sampler for animal models to make Bayesian inferences from flat priors. A chain of 500,000 Gibbs samples was thinned to every 200th sample to produce a posterior distribution comprised of 2500 samples. Heritability estimates (posterior mean ± SD) were 0.16 ± 0.03 for follicle size and 0.07 ± 0.02 and 0.02 ± 0.01 for pregnancy rate as a trait of the female and service sire, respectively. Genetic correlations were all < 0.10 and did not approach significance. Results indicate that while follicle size is of greater heritability than pregnancy rate, its usefulness to improve reproductive rate is greatest as an ancillary phenotype in multiple trait selection.