Submitted to: Midwestern Section of the American Society of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: November 26, 2004
Publication Date: September 1, 2005
Citation: Cushman, R.A., Allan, M.F., Snowder, G.D., Thallman, R.M., Echternkamp, S.E. 2005. Evaluation of ovulation rate and ovarian phenotype in puberal heifers from a cattle population selected for multiple births [abstract]. Journal of Animal Science. 83 (Supplement 2):86-87. Technical Abstract: Long-term selection for increased ovulation rate (1984 - 2002) has resulted in a unique ovarian phenotype in the MARC Twinner cattle population. Ovulation rate and frequency of bilateral ovulations were examined in heifers (n = 3910) in this population. Bilateral ovulations (one CL on each ovary) were of interest because bilateral pregnancies result in decreased dystocia and increased calf survival in cows with twin pregnancies. Heifers (12 - 18 mos. of age) were evaluated by ovarian palpation per rectum for 7.6 +/ 0.03 estrous cycles. Ovulation rate increased linearly at a rate of 0.026 CL per year, and currently averages 1.5 +/ 0.04 CL per estrous cycle. Concurrent with the increase in ovulation rate, the frequency of triplet ovulations increased from 0% to 2.3 +/ 0.8% (P < 0.0001). Ovulation rate of both the right and left ovary increased equally at a rate of 0.013 CL per year, and mean ovulation rate of the right ovary remained greater than mean ovulation rate of the left ovary throughout the study (0.66 vs. 0.55 +/ 0.003 CL per estrous cycle, P < 0.0001). The proportion of bilateral ovulations averaged 54.5 +/ 0.8%, a value greater than the predicted 49.5%. Because triplet pregnancies increase the incidence of inter-sex pregnancies and subsequent incidence of freemartins, selection pressure on ovulation rate may need to be adjusted in the MARC Twinner population. Based on the greater than expected proportion of bilateral ovulations in the population, this may be a trait that is beneficial for improving bovine reproductive efficiency and that may respond to selection. Understanding factors controlling the increased functional activity of the right ovary and bilateral ovulations may provide further insights into the mechanisms controlling follicle selection, and provide methods to improve reproductive management of cattle.