Pregnant Mares Grazing a Novel Endophyte-Infected Tall Fescue Foal Normally

Abstract These experiments were conducted to determine if pregnant mares grazing a novel endophyte tall fescue (NETF) pasture would have satisfactory foaling outcomes. The hypotheses tested were that mares grazing the NETF pasture or an orchardgrass/Kentucky bluegrass (OGBG) pasture would have statistically equivalent (1) serum progesterone, estradiol, and prolactin concentrations, (2) blood chemistry analyte concentrations, and (3) palmar artery sizes. In addition, foals born on the respective pastures would grow at comparable rates. Over 4.5 months, during each of two summers, 12 foaling mares were placed on either NETF or OGBG pastures (n = 6 mares/pasture/year). There were no differences in the blood sample concentrations of progesterone, estradiol, prolactin, and chemistry analytes between the groups. Combined uterine placental thickness and placental weights were not different between the two groups of mares, and foals grew at equivalent rates. The diameter of the palmar artery of each mare was measured via Doppler ultrasonography as a bioassay for consumption of ergot alkaloids of fescue pastures. Diameters were not different between mares grazing NETF versus OGBG pastures. However, palmar artery diameters of nonpregnant mares grazing a pasture of toxic Kentucky 31 tall fescue were reduced compared to mares on the NETF or OGBG pastures. Pasture analyses demonstrated that the NETF was endophyte infected but produced no or trace amounts of ergovaline. In summary, there were no differences in any variable tested between mares grazing the new, NETF fescue pasture, compared with mares grazing a standard OGBG pasture.