Reproductive rates of feral horses and burros

We used blood serum concentrations of reproductive hormones to estimate pregnancy rates in 553 feral horses (Equus caballus) from populations in Nevada, Oregon, and Wyoming and 173 burros (E. asinus) from California. We determined levels of progesterone (PROG), pregnant female's (mare's) s...

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Bibliographic Details
Published in:The Journal of wildlife management 1989-10, Vol.53 (4), p.916-924
Main Authors: Wolfe, M.L. (Utah State University, Logan, UT), Ellis, L.C, MacMullen, R
Format: Article
Language:English
Subjects:
ANE
Animal and plant ecology
Animal, plant and microbial ecology
Animals
ASNO
ASSES
Biological and medical sciences
BREEDS
CABALLOS
CALIFORNIA
CALIFORNIE
CHEVAL
COLORADO
Demecology
Demography
Digital rectal examination
Equus asinus
Equus caballus
FAUNE ET FLORE SAUVAGES
Foals
Fundamental and applied biological sciences. Psychology
GESTACION
GESTATION
GESTION
Hormones
HORSES
Lactation
Mammalia
MANAGEMENT
Martian landforms
NEVADA
OREGON
PERFORMANCE DE REPRODUCTION
PREGNANCY
Pregnancy rate
PROGESTERONA
PROGESTERONE
RACE
RAZAS
Reproduction
REPRODUCTIVIDAD
REPRODUCTIVITY
Vertebrata
VIDA SILVESTRE
WILDLIFE
WYOMING
Yearlings
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Summary:We used blood serum concentrations of reproductive hormones to estimate pregnancy rates in 553 feral horses (Equus caballus) from populations in Nevada, Oregon, and Wyoming and 173 burros (E. asinus) from California. We determined levels of progesterone (PROG), pregnant female's (mare's) serum gonadotropin (PMSG), and estradiol-17β (EST) by radioimmunoassay (RIA) procedures. Pregnancy determination based on all 3 hormone criteria correctly classified pregnancy status diagnosed by rectal palpation in 86.7% of 113 horses examined. Progesterone levels ≥2.00 ng/mL were the most reliable endocrine criterion for pregnancy diagnosis (accuracy rate = 81.8%) and correctly predicted ultimate reproductive performance in 89.4% of 38 radio-collared horses. Mean incidence of pregnancy among mares ≥2 years old in composite samples from Nevada, Oregon, and Wyoming was 57.0, 61.0, and 81.4%, respectively. Pregnancy rates did not differ significantly between lactating and non-lactating mares. Pregnancies among yearling mares were confirmed by rectal palpation and lactation rates of 22.2 and 11.9% among 2-year-old animals in Nevada and Wyoming, respectively. Agreement between pregnancy rates of 37 burros estimated by rectal palpation and PROG levels (≥2.00 ng/mL) was 73.0%. Mean apparent incidence of pregnancy in burros ≥2 years old was 72.3%; 25% of the yearlings were pregnant.
ISSN:0022-541X
1937-2817
DOI:10.2307/3809588