Pregnancy disruption in artificially inseminated domestic horse mares as a counterstrategy against potential infanticide1

Abstract

In a previous study, we suggested that the common practice of transporting a mare for mating and then bringing her back to an environment that also contains males that did not sire the fetus may be a major cause of high percentages of pregnancy disruption in domestic horses. In this study, we tested whether disruption of pregnancies induced by AI occurs as frequently as after mating with a strange stallion away from home and is affected by the same factors in the home social environment. Based on 77 records, the probability of pregnancy disruption after AI depended on the social environment in which the mare was maintained after mating and the number of foals the mare had delivered in the past. Also after AI, as with natural matings away from home, the probability of pregnancy disruption was higher when the mare had no male company in her enclosure but stallions or geldings were present in an adjacent enclosure than when the mare was sharing the enclosure with geldings (generalized linear mixed model = 8.68, = 0.007, odds ratio = 8.17). These data support the prediction that the mare perceives conception after AI equally to natural mating with a strange stallion. The results suggested pregnancy disruption may be stimulated by the social circumstances of the home environment in mares artificially inseminated as in mares mated naturally away from home. The practical implications of this result is that after AI, to reduce risk of pregnancy disruption and improve welfare, horse breeders should place the pregnant mare into an environment with no stallion or stallions/gelding or geldings or to an enclosure together with the male or males.

Reproductive suppression and longevity in human birth cohorts

“…Following earlier research into reproductive suppression in humans (Catalano et al, ), we specified our independent variable as the odds of death among Swedes aged 1 to 9. Theoretical and empirical literature attributes reproductive suppression, at least in part, to signals of death among conspecifics between their birth and the onset of reproductive capacity (Bartoš et al, ; Labov, ; Palombit, ; Roberts et al, ). Research in humans excluded infant deaths from the exposure variable because many of the infants who die in any year will have been in gestation during that year.…”

“…The theory of reproductive suppression posits that natural selection has conserved mechanisms that enhance the fitness of mammalian females by terminating pregnancy when the environment threatens the survival of young conspecifics (Beehner & Lu, ; de Catanzaro & Macniven, ; Hrdy, ; Labov, ; Labov, Huck, Elwood, & Brooks, ; Wasser & Barash, ; Wasser & Norton, ). The literature reports evidence of such mechanisms in several species (Bartoš et al, ; Bartoš, Bartošová, & Pluháček, ; Bruce, ; Elwood & Kennedy, ; Huck, Bracken, & Lisk, ; Palombit, ; Roberts, Lu, Bergman, & Beehner, )…”

Behavioral Factors Affecting Reproduction in Domestic Horses: Sociobiological Approach

“…We have investigated the problem in three subsequent reports where we described detailed methods and statistical analysis [48,59,60] and hence we will avoid presenting these details here. Basic tested hypothesis was that if the domestic horse mare was removed from her home environment and transported elsewhere for mating and then returned back into her home environment, containing a stallion (and/or gelding) who is not sire of her fetus, she would be more likely to disrupt her pregnancy than a mare living in an environment with the sire of her fetus.…”

“…This basic hypothesis was tested in the first study [48]. In the second step we investigated if a mare may consider pregnancy caused by artificial insemination as a pregnancy induced by a strange stallion [59], and finally we elucidated what happens when an out of home mated mare returns into male-free environment [60].…”

“…The results suggested that pregnancy disruption may equally be stimulated by the Figure 3. Proportion of pregnancy disruption according to social environment after AI of the mare according to social environment of the mare (reprinted from [59], permission for reuse provided by Oxford University Press).…”