The effect of shelter design on shelter use by Icelandic horses in the winter period

Little is known about the effect of shelter design on sheltering behavior in horses. This study investigates shelter use by Icelandic horses kept outdoors 24 hours a day during the winter in Denmark and whether shelter use and levels of fecal cortisol metabolites (FCMs) are affected by (1) the number of entrances (1 vs. 2) and (2) a partition inside the shelter. The effects of weather conditions on shelter use are also investigated. Thirty-two Icelandic horses participated in the study. The horses were pastured in 8 groups of 4 horses, and each group had access to a shelter (30 m2), which in the first study period (5 weeks, Dec-Jan) had either 1 or 2 entrances (n = 4 groups per treatment). In the second study period (5 weeks, Jan-Feb), all shelters had 2 entrances and half were equipped with a partition inside the shelter (n = 4 groups per treatment). Infrared cameras were placed inside all shelters for recording of shelter use. Feces were collected weekly during the last 3 weeks of each study period. We found that groups with 2 entrances to their shelter used the shelters significantly more than groups with only 1 entrance (% pictures with at least 1 horse inside, median [25;75%]: 2 entrances: 12.6 [7;20] vs. 1 entrance: 3.0 [2;4], P = 0.029). In addition, horses with 1 entrance had significantly increased FCM levels (ng/g, mean ± SE: 2 entrances: 6.8 ± 0.5 vs. 1 entrance: 10.0 ± 1.2, P = 0.019). The partitions did not affect shelter use or FCM levels. In both study periods, the shelters were used mainly at night (light vs. dark hours: P < 0.001), and daily average temperatures below zero degree Celsius increased shelter use. We conclude that entrance conditions are crucial to the use of shelters by Icelandic horses during winter.