Pregnancy rates and sexual behavior under pasture breeding conditions in mares.
Abstract: Pony mares (n=480) and 16 stallions were assigned to four herds of 60 mares and one stallion (large herds) and to 12 herds of 20 mares and one stallion (small herds). The stallions remained with the herds continuously for all of the large herds and seven of the small herds. In the five remaining small herds the stallion was put into a herd for three hours every two days for 12 observation periods. Pregnancy rates and day of ovulation were estimated by size of embryonal enlargements. Mean pregnancy rates of 51% and 54% were obtained in the small herds and 42% in the large herds during a 48-day period (equivalent to two estrous cycles). Pregnancy rates for herds with the stallion present continuously were higher (P<0.01) for the small herds than for the large herds for days 1-24 (42% versus 19%). There was no effect of herd size on number of mares becoming pregnant per herd on days 1-24, but more mares (P<0.01) became pregnant during days 25-48 in the large herds (13.2 mares per herd versus 1.8). In the herds in which the stallion was present intermittently, the number of times that the stallion rebred the same mare when more than one mare was in estrus was greater (P<0.01) than what would be expected to occur by chance (observed, 21%; expected, 11%). Repeated breeding of the same mare seemed related to the availability or activity of the mare, since such mares more frequently followed and positioned themselves in the vicinity of the stallion. Most of the interferences by a mare which involved keeping the stallion and another mare apart were directed at the mare, whereas most of the interferences during mounting were directed at the stallion (P<0.01). Mares were more likely (P<0.01) to interfere when in estrus than when in nonestrus. When interfering mares were in nonestrus, their hostility was usually directed at the stallion (92%), whereas when in estrus their interference was more frequently directed at a mare (73%, P<0.01).
Publication Date: 1983-09-01 PubMed ID: 16725849DOI: 10.1016/0093-691x(83)90067-5Google Scholar: Lookup
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Summary
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This study explores the effects of herd size, constant stallion presence, and mare behavior on pregnancy rates in pasture breeding conditions using a sample of pony mares and stallions. The results show that small herds with constant stallion presence yielded higher pregnancy rates and certain behaviors among mares, such as repeated breeding and interference during breeding, appear with more frequency under certain conditions.
Experimental Design
- The research involved 480 pony mares and 16 stallions, grouped into a mix of small and large herds. Small herds contained 20 mares and one stallion, while large herds housed 60 mares and one stallion.
- In some herds, the stallions remained constantly, but in others, they were introduced for only three hours every two days.
- The study extended over 12 observation periods, with a focus on estimating pregnancy rates and days of ovulation.
Key Findings
- Small herds produced a mean pregnancy rate of 51%-54% and large herds, 42%, over a 48-day period equivalent to two estrous cycles. Thus, more mares conceived in smaller herds during the 24-day period with the constant presence of the stallion.
- Interestingly, it was found that more mares in large herds got pregnant during days 25-48. This could be due to larger mating opportunities after the initial estrous cycle.
- In herds where the stallion was intermittently present, it was noticed that the stallion rebred with the same mare more often than expected when more than one mare was in heat. This suggests that the availability or activity of a mare plays a role in repeated breeding instances.
Impact of Mare Behavior on Breeding Success
- The study evaluated interferences by mares in the mating process. It was found that during mounting, mares interfered more frequently with the stallion. However, when a mare sought to separate the stallion and another mare, her interference was mostly directed at the other mare.
- In estrous phases, mares were more likely to interfere compared to non-estrus periods. This behavioral pattern indicates that the reproductive or sexual state of the mares significantly affects their interaction with the stallion and other mares, potentially influencing overall breeding success.
Cite This Article
APA
Ginther OJ, Scraba ST, Nuti LC.
(1983).
Pregnancy rates and sexual behavior under pasture breeding conditions in mares.
Theriogenology, 20(3), 333-345.
https://doi.org/10.1016/0093-691x(83)90067-5 Publication
Researcher Affiliations
- Department of Veterinary Science, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
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