title: A biological embryo-reduction mechanism for the elimination of excess embryos in mares.
abstract: Only one embryo was found in each of 15 pregnant mares in which multiple, synchronous (0 or 1 day apart) ovulations were induced with a pituitary extract. In the brood-farm mares, fewer (P<.05) twin pregnancies were associated with synchronous, double ovulations (0 39 ), than with asynchronous, double ovulations (9 57 ). Higher (P<.05) pregnancy rates (number of mares pregnant, regardless of number of embryos) were obtained in pituitary extract-treated mares with multiple, synchronous ovulations (15 18 ) than in treated mares with single ovulations (6 14 ). Similarily, pregnancy rates were higher (P<.01) in brood-farm mares with double, synchronous ovulations (39 47 ) than in brood-farm mares with single ovulations (1320 2426 ). Our interpretation is that ova produced by synchronous, double ovulations are viable and fertilizable (indicated by higher pregnancy rates), but that one of the resulting embryos is eliminated (indicated by the absence of twins).
authors.affiliation: Department of Veterinary Science, University of Wisconsin Madison, Wisconsin 53706 USA; Equiculture, Inc., Cross Plains, Wisconsin 53528 USA.
authors.forename: O J
authors.initials: OJ
authors.lastname: Ginther
authors.forename: R H
authors.initials: RH
authors.lastname: Douglas
authors.forename: G L
authors.initials: GL
authors.lastname: Woods