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Effect of reproductive status on twinning and on side of ovulation and embryo attachment in mares



Effect of reproductive status on twinning and on side of ovulation and embryo attachment in mares



Theriogenology 20(4): 383-396



Brood-farm records were used to test several hypotheses concerning twinning and inequalities in the side of ovulation and embryo attachment. Ovulation occurred more frequently (P < 0.05) from the left ovary (61% vs. 39%) in maiden mares, but with equal frequency from either ovary in lactating and barren mares. The embryo attached more often (P < 0.05) to the left horn in lactating mares (60%) and to the right horn in barren (59%)and maiden (67%) mares. Double ovulations and twin embryos were diagnosed more frequently (P < 0.05) in barren mares (11% and 6%, respectively) than in lactating mares (5% and 1%). Pregnancy rates for double ovulations were affected (P < 0.01) by the length of the interval between the 2 ovulations (0 days, 83%; 2 days, 87%; 4 days, 67%; 6 days, 54%; 8 days or more, 38%). Pregnancy rates were higher (P < 0.01) for double ovulations 0 or 2 days apart (84%) than for single ovulations (54%). Twins were diagnosed more frequently (P < 0.05) when double ovulations were 2 or more days apart (9/32) than when the ovulations were synchronous (0/19). An embryo-reduction mechanism exists in mares for the elimination of excess embryos and, evidently, the mechanism loses its effectiveness when the embryos originate from asynchronous ovulations.

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Accession: 001189232

Download citation: RISBibTeXText

PMID: 16725855

DOI: 10.1016/0093-691x(83)90199-1



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