Effect of energy supplementation on gravid mares grazing endophyte-infected fescue

Abstract

Summary Fourteen Arabian and Quarter horse gravid mares were randomly assigned by breeding date and breed to individual .5 hectare Ky-31 endophyte-infected pastures. Mares in half of the 14 pastures received 50% of the National Research Council (NRC) recommended daily energy allowance as cracked corn during the last 90 days of gestation (E) and the control mares received no energy supplementation (NE). Body weights and blood samples for estrogen, progesterone and prolactin were collected at 29 d intervals and at foaling. Serum levels of estrogen (pg/ml), progesterone (ng/ml) and prolactin (ng/ml were: 30.5, and 27.9±1.3; 4.2 and 4.9 ± .8; 7.6 and 7.4 ± .9 for E and NE, respectively and were not different (P>.05). Of the first 7 mares to foal, with an average gestation length of 360 days, all exhibited dystocia. Four of these mares died as a result of dystocia and only 1 foal survived due to a Caesarean section. Based on subjective observation, none of these mares exhibited the classical or normal signs of approaching parturition (i.e., udder development, “hollowing” of the paralumbar fossa and softening of the gluteal muscles). These mares all delivered live foals and lactated. The supplementation of 50% NRC energy requirements for gravid mares grazing endophyte infected fescue appears to be of little or no benefit for reducing symptoms of fescue toxicity. Mares that have gone beyond their normal gestation length on endophyte infected pasture appear to foal normally after removal to endophyte free fescue pastures.