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Effects of short-term early gestational exposure to endophyte-infected tall fescue diets on plasma 3,4-dihydroxyphenyl acetic acid and fetal development in mares^1,2

R. C. Youngblood^*, N. M. Filipov, B. J. Rude^*, D. L. Christiansen, R. M. Hopper, P. D. Gerard, N. S. Hill, B. P. Fitzgerald^¶ and P. L. Ryan^*,,3

^* Department of Animal and Dairy Sciences, and College of Veterinary Medicine, and and Experimental Statistics Unit, Mississippi State University, Mississippi State 39762; and Department of Crop Sciences, University of Georgia, Athens 30602; and and ^¶ Gluck Equine Research Center, University of Kentucky, Lexington 40546

³ Correspondence: 4025 Wise Center, Box 9815 (phone: 662-325-2938; fax: 662-325-8873; e-mail: Ryan{at}cvm.msstate.edu).

Consumption of wild-type (toxic) endophyte-infected tall fescue (E+) by horses during late gestation is known to adversely affect pregnancy outcome; however, little is known of the potential disruptive consequences of E+ consumption by mares during the critical phases of placentation and fetal development in early pregnancy. The objective of this study was to evaluate the detrimental effects of feeding E+ to mares during early gestation. Mares (n = 12) paired by stage of gestation (d 65 to 100) were assigned to diets (six per diet) consisting of endophyte-free (E–) or E+ tall fescue seed (50% E– or E+ tall fescue seed, 45% sweet feed, and 10% molasses fed at 1.0% of BW/d). Mares also had ad libitum access to E+ or E– annual ryegrass hay, and were fed diets for 10 d. Following removal from the tall fescue diet on d 11, mares were placed on common bermudagrass pasture and monitored until d 21. Morning and evening rectal temperatures were recorded and daily blood samples were collected for progesterone and prolactin (PRL) analyses, whereas samples for 3,4-dihydroxyphenyl acetic acid (a catecholamine metabolite) analysis were collected on alternate days. For clinical chemistry analysis, blood samples were collected on d 0, 5, 10 and 21. Daily urine samples were collected for ergot alkaloid analysis, and ultrasonography was performed for presence of echogenic material in fetal fluids. Rectal temperatures (E+ 37.76 ± 0.03; E– 37.84 ± 0.03°C) and serum PRL concentrations (E+ 14.06 ± 0.76; E– 12.11 ± 0.76 ng/mL) did not differ (P = 0.96) between treatments. Measuring the change in basal serum concentration from d 0 over time, progesterone concentrations did not differ (–0.64 ± 1.49 and –0.55 ± 1.47 ng/mL for E+ and E– mares, respectively). There was no negative pregnancy outcome, and ultrasonography indicated no increase in echogenic material in fetal fluids. Plasma 3,4-dihydrox-yphenyl acetic acid concentrations decreased (P < 0.05) in E+ compared with E– mares (2.1 ± 0.14 and 4.4 ± 0.43 ng/mL, respectively). Urinary ergot alkaloid concentration was greater (P < 0.01) in mares consuming E+ compared with E– (532.12 ± 52.51 and 13.36 ± 2.67 ng/mg of creatinine, respectively). Although no fetal loss was observed during the current study, elevated concentrations of urinary ergot alkaloid were consistent with depressed endogenous catecholamine activity, suggestive of an endocrine disruptive effect of hypothalamic origin.

Key Words: Catecholamine • Equine Pregnancy • Ergot Alkaloid • Tall Fescue