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EFFECTS OF EXPOSING LATE-TERM PREGNANT MARES TO TOXIC AND NON-TOXIC ENDOPHYTE-INFECTED TALL FESCUE PASTURES.
Ryan, Peter1,3, Rude, Brian 1, Warren, Beth1, Boyd, Leroy1, Lang, David2, Scruggs, Daniel3, Hopper, Richard3, 1 3 2
ABSTRACT- Tall fescue infected with Neotyphodium coenophialum (E+) produce ergot alkaloids known to be toxic in late-term pregnant mares. However, a novel fescue cultivar infected with a non-toxic endophyte (NTE+) has been developed for cattle grazing but its safety for pregnant mares is unknown. The objective of this study was to evaluate the health risks of pregnant mares grazing NTE+ compared with E+ and endophyte-free fescue (E-). Mares (n = 15) were matched by expected foaling date (April-June) and placed on 5 hectare pastures (n = 5/pasture) from March 1 until day 21 postpartum (PP). Mares were monitored daily for signs of fescue toxicity. Blood was collected 3x/week up to 30 days prior to expected foaling date then 6x/week through to day 15 PP for prolactin (PRL) analysis. Urine was collected weekly for ergot alkaloid analysis and placental membranes were submitted for histopathology. Pasture endophyte infestation rates were 2.3%, 63% and 91% in March and 1.5%, 92% and 91% in May for E-, NTE+ and E+ pastures, respectively. Of the infected tillers sampled in each pasture during May, 6% of the E- and NTE+ were positive for ergot alkaloids while 100% of the E+ tested positive. Only mares grazing E+ showed symptoms consistent with fescue toxicity which included agalactia (4/5), compromised delivery (2/5), retained placenta (3/5), and one mare aborted at 301 days gestation. Moreover, mares grazing E+ pastures had longer (p<0.05) gestation (353 ± 3.2 days) compared to those exposed to E- and NTE+ (333 ± 3.2 and 340 ± 5.4, respectively). Mean ergot alkaloid content of urine was highest (p<0.01) in E+ (38.5 ng/mg creatinine) compared with NTE+ and E- mares (5.9 and 3.4, ng/mg creatinine, respectively; SEM = 5.74). Milk sampled weekly for 21 days PP tested negative for ergot alkaloids. Placental measurements showed increased (p<0.03) thickening of the cervical aspect of the placenta in E+ compared with NTE+ and E- mares (4.5, 1.6 and 1.6 mm, respectively, SEM = 0.65). Peak PRL serum concentrations of mares tended to differ (p< 0.07) at peripartum and were 73.9, 66.4 and 38.7 ng/ml (SEM = 10.28) for E-, NTE+ and E+ exposed mares, respectively. These findings suggest that there is minimal or no health risk to pregnant mares grazing non-toxic, endophyte-infected tall fescue. (Funded by MAFES and Pennington Seed Inc., GA).
KEY WORDS: equine, pregnancy, toxic, non-toxic endophyte-infected fescue