Title

Prolactin Administration to Seasonally Anestrous Mares: Reproductive, Metabolic, and Hair-Shedding Responses

Document Type

Article

Publication Date

1-1-1997

Abstract

Eight pony mares received 4 mg of recombinant porcine prolactin (rpPRL) daily for 45 d beginning on January 15; eight control mares received vehicle. Reproductive end points and various indicators of metabolism, hair shedding, and thyroid activity were monitored. Prolactin concentrations peaked in mares treated with rpPRL at 94 ± 19 ng/mL 2 h after injection and were 5.1 ± 1.7 ng/mL 24 h after injection. Treatment with rpPRL increased (P < .01) hair shedding within 14 d, which peaked at 28 d and then dropped precipitously. Binding of 125I-equine prolactin confirmed that antibodies were present in rpPRL-treated mares by 28 d, thus only data up to that time are included herein. The percentage of mares in estrus after 17 d of treatment was greater (P < .05) for mares treated with rpPRL than for controls, although the average day of estrus onset did not differ (P > .1). The date of first ovulation, determined from plasma progesterone concentrations, was hastened (P < .005) in mares treated with rpPRL (February 6 ± 3 d) relative to control mares (March 14 ± 6 d). Concentrations of insulin-like growth factor I and nonesterified fatty acids were not affected (P > .1) by treatment with rpPRL but did vary (P < .05) over time. There were minor differences between groups in thyroid hormone secretion. Various assessments of glucose and insulin indicated no perturbation (P > .1) due to treatment with rpPRL. We conclude that prolactin mediates the onset of vernal hair shedding in mares and is in some way involved with ovulation.

Publication Source (Journal or Book title)

Journal of Animal Science

First Page

1092

Last Page

1099

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