115 Effect of an enriched social environment on social maturation of horses

Abstract

Conventional husbandry practices rarely allow for sociality of horses. Under natural conditions, horses learn the social codes of their group mates during the first years of life. Horses raised in box stalls have more aggressive interactions with humans than horses housed in a group setting in a pasture. Such conditions can potentially compromise the well-being of the horses. The study aimed at providing Information on the temporal evolution of the young horse's behavior in a social group to estimate better the exact age of social maturity. The study was run in a breeding stud for sport horses born and raised in large social all-age groups (20–60 horses), always outdoors on large pastures and fed roughage only. Salt lick was available. From the age of 4 years, the behavior of 9 horses was observed daily during daytime (6 h between 8:00 a.m. and 8:00 p.m.) between June and August each year for 3 consecutive years. Each horse was observed for a total of at least 90 h and its social interactions (defensive, offensive, or affiliative) were recorded. The data was analyzed with a GLMM. The type of interaction was considered a fixed factor in interaction with age and season. The identity of horses was considered a random factor. We found that 4yrs-old horses had fewer defensive interactions than 5- and 6yrs-old horses (4yrs-5yrs P < 0.0001, 4yrs-6yrs P < 0.001). The affiliative and offensive interactions decreased continuously fromthe age of 4 to 6 yrs with 5yrs old showing in between levels (Affiliative: 4yrs-5yrs P < 0.0001, 5yrs-6yrs P < 0.001, 4yrs-6yrs P < 0.001; Offensive: 5yrs-6yrs P = 0.009, 4yrs-5yrs P < 0.001, 4yrs-6yrs P < 0.001). While getting older, horses expressed less offensive agonistic behavior and more defensive behavior suggesting a phenomenon of social maturation from the age of 4 to 6 years. This might be the consequence of a better ability to establish and respect the group's dominance hierarchy. It is also possible that more mature horses stay closer to same-rank individuals, unlike younger ones, decreasing then the risk of offensive interactions. The fact that the decrease in affiliative interactions was associated with a decrease in offensive interactions go along with the hypothesis of a social maturation and the development of better socio-cognitive skills. This development of social behavior questions the fact that many horses are traditionally isolated from congeners when they start working, from the age of 2, latest 3 years old. Our results suggest that such horses are excluded from a social group during a sensitive period of social maturation. This could induce a lack of social skills that could be necessary later for interacting normal with congeners and humans.