Submitted to: Theriogenology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2001
Publication Date: 4/1/2002
Citation: BURKE, J.M., RORIE, R.W. 2002. CHANGES IN OVARIAN FUNCTION IN MATURE BEEF COWS GRAZING ENDOPHYTE-INFECTED TALL FESCUE. THERIOGENOLOGY. 57:1733-1742. Interpretive Summary: Tall fescue toxicosis is a condition associated with grazing endophyte- infected tall fescue that can reduce economic outcome of a cow-calf operation. Reduced income results from decreased pregnancy and calving rates and reduced weaning weights of calves. The current study examined follicular and luteal development and function in mature, lactating beef cows grazing endophyte-free or infected tall fescue during the early postpartum period. Diameter of the largest follicle, which contains the egg that can ovulate, tended to be smaller, especially in mid cycle, and number of 6 to 9 mm follicles was reduced for much of the cycle for cows grazing endophyte-infected fescue, but ovarian hormone concentrations were similar between treatment groups. This study informs producers and extension agents that under good management conditions, mature cows can graze infected fescue without harm to ovarian function.
Technical Abstract: The objective was to examine follicular and luteal development and function in mature, lactating beef cows grazing endophyte-free (E-) or endophyte-infected (E+) tall fescue during the early postpartum period. Angus, Hereford, and Angus Hereford cows were exposed to pasture for 37 to 39 d before synchronized estrus. Serum concentrations of prolactin were evaluated during the luteal phase before the synchronized estrus. Every Monday, Wednesday, and Friday for one estrous cycle ovaries were monitored by transrectal ultrasonography and blood collected for determination of serum concentrations of progesterone and estradiol 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 body condition of cows and weight of cows and calves (P<0.001). Neither serum concentrations of progesterone or estradiol, nor diameter of the CL differed between treatments. Diameter of the largest follicle tended to be smaller for cows grazing E+ fescue, especially between Days 8 and 12 of the estrous cycle (P<0.08). Numbers of Class 1 (3 to 5 mm) and 3 (>10 mm) follicles were similar between treatments, but number of Class 2 (6 to 9 mm) follicles was reduced in E+ cows for most of the cycle (P<0.03). Length of synchronized estrous cycle, days open, calving interval, and pregnancy rate at 30, 45, 60, and 90 days post-breeding was similar among treatment groups. Even though follicular dynamics (diameter of the largest follicle and number of Class 2 follicles) were altered in cows grazing E+ tall fescue, follicular function was apparently not affected by ergot alkaloids.