Submitted to: Society for the Study of Reproduction Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2001
Publication Date: 7/1/2001
Citation: BURKE, J.M., RORIE, R.W., PERRY, G.A., KEISLER, D.H. 2001. CHANGES IN OVARIAN FUNCTION IN MATURE BEEF COWS GRAZING ENDOPHYTE-INFECTED (E+) TALL FESCUE. SOCIETY FOR THE STUDY OF REPRODUCTION ANNUAL MEETING. 64(Suppl. 1):344.
Technical Abstract: The objective was to examine follicular and luteal development and function and changes in serum concentrations of leptin in mature, lactating beef cows grazing endophyte-free (E-; n = 12) or E+ (n = 16) tall fescue during the early postpartum period. Angus, Hereford, and Angus x Hereford cows were exposed to pasture for 37 to 39 d before synchronized estrus. Ovaries were monitored for one estrous cycle and blood collected for determination of serum concentrations of progesterone, estradiol, prolactin, and leptin in cows that responded to synchronization. Signs of fescue toxicosis in E+ cows included decreased serum concentrations of prolactin (84.9 +/- 13.6 vs 32.3 +/- 12.0 pg/ml; P<0.009) measured during luteal phase (Day 37 of grazing) and decreased BCS (0 +/- 0.2 vs -0.9 +/- 0.2 loss in BCS; P<0.02) and body weight (15.2 +/- 7.0 vs -10.0 +/- 5.7 kg change in body weight; P<0.01) during first 60 d of grazing. Neither serum concentrations of progesterone or estradiol, nor diameter of the CL differed between treatments. Diameter of the largest follicle was reduced between D 8 and 12 of the estrous cycle in E+ cows (D 0 = first day of standing estrus; P<0.08). Numbers of Class 1 (3 to 5 mm) and 3 (>9 mm) follicles were not different between treatments, but number of Class 2 (6 to 9 mm) follicles was reduced in E+ cows for much of the cycle [yE- = 0.81 + 0.26x - 0.031x2 + (1.19 x 10-3)x3 and yE+ = 0.46 + 0.93x - 0.13x2 + (4.5 x 10-3)x3; pasture x d, P<0.009; R2 = 0.07]. Neither length of cycle nor serum concentrations of leptin measured during the estrous cycle differed between treatments. In summary, while follicular dynamics were altered in cows grazing E+ tall fescue, function did not appear to be affected.