Prolactin administration to seasonally anestrous mares: reproductive, metabolic, and hair-shedding responses.
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 < .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.
Thompson
D L
DL
Department of Animal Science, Louisiana Agricultural Experiment Station, Louisiana State University Agricultural Center, Baton Rouge 70803-4210, USA.
Hoffman
R
R
DePew
C L
CL
D000780:Anestrus / Q000502:physiology*; D000818:Animals; D000906:Antibodies / Q000032:analysis / Q000276:immunology; D001786:Blood Glucose / Q000032:analysis / Q000378:metabolism; D004971:Estrus / Q000502:physiology; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D005298:Fertility / Q000187:drug effects / Q000502:physiology; D005640:Follicle Stimulating Hormone / Q000097:blood; D006062:Gonadotropins / Q000378:metabolism*; D006197:Hair / Q000187:drug effects / Q000502:physiology*; D006736:Horses / Q000097:blood / Q000378:metabolism* / Q000502:physiology*; D006854:Hydrocortisone / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000378:metabolism; D007457:Iodine Radioisotopes; D007986:Luteinizing Hormone / Q000097:blood; D006080:Ovarian Follicle / Q000187:drug effects / Q000502:physiology; D010053:Ovary / Q000000981:diagnostic imaging / Q000187:drug effects / Q000502:physiology; D010060:Ovulation / Q000187:drug effects / Q000502:physiology; D011388:Prolactin / Q000008:administration & dosage / Q000276:immunology / Q000494:pharmacology*; D012098:Reproduction / Q000187:drug effects / Q000502:physiology*; D012621:Seasons; D014463:Ultrasonography
D000906:Antibodies; D001786:Blood Glucose; D005230:Fatty Acids, Nonesterified; D006062:Gonadotropins; D007457:Iodine Radioisotopes; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D006854:Hydrocortisone