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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Livestock Bio-Systems » Research » Publications at this Location » Publication #178393
Title: EVALUATION OF OVULATION RATE AND OVARIAN PHENOTYPE IN PUBERAL HEIFERS FROM A CATTLE POPULATION SELECTED FOR INCREASED OVULATION RATE

Author
item Cushman, Robert - Bob
item Allan, Mark
item Snowder, Gary
item Thallman, Richard - Mark
item Echternkamp, Sherrill

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/7/2005
Publication Date: 8/20/2005
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 increased ovulation rate. Journal of Animal Science. 83(8):1839-1844.

Interpretive Summary: Bilateral pregnancies (1 CL/ovary) result in decreased dystocia and increased calf survival in cows selected to produce twin calves. Analysis was performed on palpation data collect during the history of the project to re-examine trends in ovulation rate change and determine what has happened to the frequency of bilateral ovulations as ovulation rate has increased due to selection. Ovulation rate increased linearly at a rate of 0.026 CL per year, and currently averages 1.48 +/ 0.04 CL per estrous cycle in heifers. Concurrent with the increase in ovulation rate, the frequency of triplet ovulations increased from 0% to 2.3 +/ 0.8%. 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. The proportion of bilateral ovulations averaged 55.7 +/ 0.7%, a value greater than the predicted 49.5%. Because triplet pregnancies increase the incidence of pregnancies gestating fetuses of opposite sexes and subsequent incidence of freemartins, selection pressure on ovulation rate may need to be adjusted in the MARC Twinner population. The proportion of bilateral ovulations in the population is greater than expected, and this may be an economically important trait, which will respond to selection and be beneficial for improving bovine reproductive efficiency. 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.

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 by rectal palpation in 29,547 estrous cycles for 3,910 heifers (12-18 months of age) in this population. Bilateral ovulations (1 CL on each ovary) were of interest because bilateral twin pregnancies result in decreased dystocia and increased calf survival. Ovulation rate increased linearly at a rate of 0.026 CL per year, and currently averages 1.48 +/ 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). Ovulation rate of one ovary was negatively correlated (P < 0.0001; r = -0.07) with ovulation rate of the same ovary in the previous estrous cycle but positively correlated (P < 0.0001; r = 0.13) with the contralateral ovary of the previous estrous cycle. The proportion of bilateral ovulations averaged 55.7 +/ 0.7%, a value greater than the predicted 49.5% (P < 0.0001). In addition to dystocia and retained placenta, triplet pregnancies increase the incidence of pregnancies gestating fetuses of opposite sexes and subsequent incidence of freemartins, selection pressure on ovulation rate may need to be adjusted in the MARC Twinner population. The proportion of bilateral ovulations in the population is greater than expected, and this may be an economically important trait, which will respond to selection and be beneficial for improving bovine reproductive efficiency. 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.