Behavioral Factors Affecting Reproduction in Domestic Horses: Sociobiological Approach

Abstract

Fetal loss is a common phenomenon in domestic horses, being usually highest (up to 40%) of all domestic ungulates. However, in all studies investigating this problem, sociobiological approach, such as conflict between the evolutionary interests of individuals of the two sexes, has been neglected. Here we summarize results of three consecutive studies considering infanticide as a male's reproductive strategy and a mare's counter strategies against it. When a mare was either artificially inseminated or 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 did not sire her fetus, she got into a potentially infanticidal danger. She more likely disrupted her pregnancy than a mare living in an environment with the sire of her fetus. This was highly affected by the social environment. Lowest percentage of pregnancy disruption can be achieved when the pregnant mare was released into an enclosure shared with the non-sire male whom she can "convince" he is the father of her expected foal by promiscuous mating. The effects of social environment leading to pregnancy block and/or disruption may thus explain substantial part of the high incidence of domestic horse fetal loss.

How to escape male infanticide: mechanisms for avoiding or terminating pregnancy in mammals

“…1d). Thus in the domestic horse (Bartoš et al, 2019) and in domestic dog females known to be pregnant (Bartoš et al 2016), physical contact with the home male was actually needed to maintain pregnancy. In the domestic horse, pregnant females that were released into an enclosure with non‐paternal males showed repeated sexual activity (Bartoš et al 2011, 2015).…”

“…Thus, for example, while there have been considerable advances in discovering the mechanism of pregnancy blocking in the house mouse (DeCatanzaro et al 2001, Beaton & deCatanzaro 2004, 2005, DeCatanzaro et al 2006, Becker & Hurst 2009, DeCatanzaro 2010, 2011, Guzzo et al 2012, DeCatanzaro 2015; see also the extensive review by Zipple et al 2019b), the same mechanisms cannot explain pre‐implantation pregnancy block in the domestic dog Canis lupus familiaris (Bartoš et al 2016) or the post‐implantation pregnancy disruption described in the domestic horse (Bartoš et al 2019) and domestic dog (Bartoš et al 2016). When female dogs and horses were permitted close physical contact with non‐sire males, the probability of maintaining pregnancy was higher than in females in visual or auditory contact with such males but prevented from direct physical contact.…”

Do infanticides occur in harem-forming equids? A test with long-term sociodemographic data in wild plains zebras

“…Males that do not hold a harem form loose bachelor groups and will eventually attempt to start a harem by 'abducting' young females, monopolizing dispersing young females or taking over a harem by replacing the stallion. In these harem-forming equids, infanticide by males is expected for several reasons (see references in Bartoš, Bartošová, & Pluháček, 2019;Ebensperger, 1998;Palombit, 2015).…”