Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 14, 2011
Publication Date: July 1, 2011
Citation: Cushman, R.A., Kuehn, L.A., Thallman, R.M., Snelling, W.M., Freetly, H.C. 2011. Using ultrasonography to determine reproductive tract development in beef heifers [abstract]. Journal of Animal Science. 89 (E-Supplement 1):418-419 (Abstract #327). Technical Abstract: Choosing replacement beef heifers is a decision with long-term implications for profitability for the cow-calf producer. If a replacement heifer fails to wean the number of calves necessary to recover her development costs, then she incurs a net loss for the ranch. To avoid such losses, it is imperative to develop technologies that aid in identifying heifers with little chance of weaning three or more calves. The first hurdle to reproductive competency is the establishment of reproductive cycles (puberty). No intensive research has evaluated the size of the ovaries or uterus in relation to reproductive status in beef heifers. Therefore, the objective of the present study was to use ultrasonography to measure the sizes of these structures and relate them to reproductive status in yearling crossbred beef heifers (n = 368). At weaning, heifers were moved to a feedlot and placed on a growing ration. At 13.6 ± 0.6 months of age (range 12 to 15 months), development of the reproductive tract was evaluated using ultrasonography. Each ovary was measured for length and height and a cross-sectional measurement of the endometrium was taken on the right side, approximately 1 cm anterior to the uterine body. Antral follicles > 3 mm and corpora lutea were counted. Percentages of Brahman, Continental, or British breeds were fitted as fixed covariates. Numbers of antral follicles increased as the percentage of Brahman influence in an individual heifer increased (P < 0.0001). There was no breed effect for ovarian size or endometrial diameter. Both ovarian size and endometrial diameter were greater in 15-month-old heifers than 12-month-old heifers (P = 0.03). The percent of heifers that had initiated reproductive cycles as determined by the presence of a corpus luteum at ultrasonography increased as age increased and as percent Brahman decreased (P = 0.001). The use of ultrasonography to evaluate the ovaries and uterus in yearling beef heifers is a practical tool to aid in determining the reproductive status of replacement heifers. *USDA is an equal opportunity provider and employer.