Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: March 12, 2007
Publication Date: June 20, 2007
Citation: Cushman, R.A., Allan, M.F., Thallman, R.M., Cundiff, L.V. 2007. Influence of breed on postpartum interval and estrous cycle length in beef cattle [abstract]. Journal of Animal Science. 85 (Supplement 1):370. (Abstract #401) Technical Abstract: Before genetic markers can be generated for fertility in beef cows, greater characterization of reproductive phenotypes is needed to understand the components of reproductive efficiency. The present study tested the hypotheses that 1) breeds vary in postpartum interval (PPI) and estrous cycle length, 2) a longer estrous cycle immediately prior to breeding increased pregnancy rates, and 3) a greater number of cycles prior to breeding increased pregnancy rates. PPI, estrous cycle length, and number of cycles prior to breeding were examined in F1 cows (n = 519) obtained from mating Hereford, Angus, and USMARC III cows to Hereford, Angus, Simmental, Limousin, Charolais, Gelbvieh, and Red Angus sires. Cows were classified as having 0, 1, 2, or 3 observed estrous cycles prior to breeding. Sire breed of the cow influenced the length of the PPI and number of cycles prior to the start of breeding (P < 0.001). Simmental-sired cows had the shortest PPI and greatest number of cycles prior to breeding while Limousin-sired cows had the longest PPI and least number of cycles prior to breeding. Cows with a greater number of cycles prior to breeding did not have greater pregnancy rates than cows that had not exhibited standing estrus prior to breeding (P = 0.87). In cows that cycled prior to breeding, the length of the estrous cycle immediately prior to breeding was influenced by dam breed and body condition score (BCS, P < 0.01). Cows out of Hereford dams had shorter estrous cycles than cows out of USMARC III or Angus dams, and estrous cycle length increased as body condition score increased. Pregnancy rate decreased as length of the estrous cycle immediately prior to breeding increased (P = 0.05; -2.2% per day of cycle length). Previously anestrous cows were just as likely to conceive as cows that had cycled prior to breeding, and an increased number of observed estrous cycles prior to breeding did not increase pregnancy rates. There may be an influence of length of the estrous cycle immediately prior to breeding on conception rates, possibly because a longer estrous cycle results in a prolonged preovulatory follicle and lower quality oocyte. Breed differences in PPI and estrous cycle length suggest that there are genetic components to these traits.