Age-Specific Pregnancy Rates in Feral Horses

Blood samples were collected from 137 feral female horses (Equus caballus) captured near Salmon, Idaho in October 1980. Serum samples were analyzed for progesterone, luteinizing hormone or pregnant mare serum gonadotropin, and estradiol-17β for evaluation of reproductive status. The mares were age c...

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Bibliographic Details
Published in:The Journal of wildlife management 1983-04, Vol.47 (2), p.422-429
Main Authors: Seal, U. S., Plotka, E. D.
Format: Article
Language:English
Subjects:
Age
Anestrus
Estrogens
Estrus cycle
Foals
Hormones
Horses
Lactation
Pregnancy
Pregnancy rate
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Summary:Blood samples were collected from 137 feral female horses (Equus caballus) captured near Salmon, Idaho in October 1980. Serum samples were analyzed for progesterone, luteinizing hormone or pregnant mare serum gonadotropin, and estradiol-17β for evaluation of reproductive status. The mares were age classified, observed for lactation, and the presence of a foal noted. A diagnosis of pregnancy was made on the basis of progesterone >2.4 ng/ml and either PMSG >13 ng/ml or estradiol-17β >69 pg/ml. Mares 1 year and older were classified as anestrus = 31, cycling = 12, possible abortions = 3, uncertain status = 6, and pregnant = 85. Age-specific pregnancy rates increased with age from 36% in the 2-year-olds to about 85% in the 6-15-year-olds. No yearlings were pregnant. Sixty-two mares, 56 with foals, were lactating. No 2-year-olds, 25% of the 3-year-olds, 43% of the 4-year-olds, and 50-75% of the 5-year and older animals were lactating. Fifty-two animals were pregnant and were lactating or had a foal at the side. Thus at least 50% of the eligible mares were pregnant in consecutive years.
ISSN:0022-541X
1937-2817
DOI:10.2307/3808515