>>>> it ensures that only his bloodline is spread, it is nature. Plus by killing her offspring he ensures the mare will go back into estrus quickly and be ready for breeding again, so to him it is win win.
This has been a commonly believed hypothesis, but there have been actual studies that do not support the idea that stallions commonly kill foals that are not theirs-- and if they do, that it gives them benefit of breeding the mare sooner, if at all. Below is an abstract of an 11 year study done on wild Przewalski horses which refuted foal killing as common and actually documented many times more cases of stallions NOT killing foals sired by other stallions when given the opportunity --
""The sexual selection hypothesis explains infanticide by males in many mammals. In our 11-year study, we investigated this hypothesis in a herd of Przewalski's horses where we had witnessed infanticidal attacks. Infanticide was highly conditional and not simply linked to takeovers. Attacks occurred in only five of 39 cases following a takeover, and DNA paternity revealed that, although infanticidal stallions were not the genetic fathers in four cases out of five, stallions present at birth did not significantly attempt to kill unrelated foals. Infanticide did not reduce birth intervals; only in one case out of five was the infanticidal stallion, the father of the next foal; mothers whose foals were attacked subsequently avoided associating with infanticidal stallions. Therefore, evidence for the sexual selection hypothesis was weak. The “human disturbance” hypothesis received some support, as only zoo bred stallions which grew up in unnatural social groups attacked foals of mares which were pregnant during takeovers.""
-----C. Feh and B. Munkhtuya
Association pour le cheval de Przewalski: TAKH, Station Biologique de la Tour du Valat, Le Sambuc, 13200 Arles, France, Charles University in Prague, Ovocny trh 5, Praha 1, 116 36, Czech Republic
Received 18 April 2007; revised 7 December 2007; accepted 24 December 2007. Available online 12 January 2008.