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Dexamethasone—Induced Parturition in Pony Mares¹

University of Wisconsin, Madison 53706

³ Address for reprint requests: Department of Meat and Animal Science, University of Wisconsin, Madison 53706.

Abstract

Twelve pregnant pony mares were assigned to a control (N=7) and treatment group (N=5). Treatment consisted of daily intramuscular injections of saline or 100 mg dexamethasone from day 321 through 324 or until parturition, whichever occurred first. Dexamethasone treatment significantly shortened gestation (P<.01). The mean length of gestation ± SE and range in days were, respectively: control mares 334.4 ± 1.2, 322 to 344 and dexamethasone-treated mares 324 ± .1, 323 to 325. All 12 foals were born live and normal in appearance; every mother lactated and produced sufficient milk to raise her foals. Twelve pony mares ovariectomized on day 140 or 210 of gestation were assigned randomly in equal numbers before the beginning of the experiment to a control and treatment group. Treatment consisted of daily intramuscular injections of 100 mg dexamethasone from day 321 through 324 of gestation. The mean length of gestation ± SE and range in days were, respectively, 323.6 ± 5.6, 305 to 338 for control mares and 326.8 ± .5, 324 to 331 for mares treated with dexamethasone. Although the means were not significantly different, dexamethasone treatment did reduce the range and variance in gestation. Four of the six treated mares foaled within the same time interval as the dexamethasone-treated mares in the first experiment suggesting that dexamethasone can induce parturition in ovariectomized mares. There was no significant difference between control and treated mares in birth weight, the presence of milk after parturition or the frequency of live birth.

¹ Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison 53706. Department of Meat and Animal Science Paper No. 688.

⁴ Present address: Route 1, Box 263, Cleveland, WI 53015.