EFFECTS OF GRAZING ENDOPHYTE-INFECTED TALL FESCUE ON ECG AND PROGESTOGEN CONCENTRATIONS FROM GESTATION DAYS 21 TO 300 IN THE MARE

The influence of grazing endophyte-infected tall fescue on endometrial cup formation and function, progestogen production, and embryonic and fetal development were examined in pregnant mares between Day 21 and Day 300 of gestation. Total immunoreactive progestogens and equine cho rionic gonadotropin (eCG) concentrations were compared between untreat ed controls (endophyte-free, n=12) and treated mares (endophyte-infect ed, n=12). There were no differences in endometrial cup formation or f unction, as determined by eCG concentrations at Days 45, 60, 75, 90 an d 120 (P > 0.05) between mares grazing endophyte-infected and endophyt e-free tall fescue. Mares grazing the endophyte-infected tall fescue h ad lower total progestogen concentrations (P < 0.01) from Days 90 to 1 20 than the mares grazing endophyte-free tall fescue. Embryonic develo pment based on mean vesicle height was not affected by endophyte expos ure. No pregnancies were lost by mares in either treatment group durin g the trial period. The results of this study indicate that grazing en dophyte-infected tall fescue between Day 21 and Day 300 does not alter endometrial cup formation and function, or result in increased pregna ncy losses during this period. Lower progestogen concentrations betwee n Days 90 and 120 with exposure to endophyte-infected tall fescue coul d reflect decreased luteal progesterone production.