Preference of domestic horses for shade in a hot, sunny environment

Provision of shade is recommended by best practice guidelines for horses living in hot, sunny environments despite a lack of research focused on potential benefits. We found in a previous study that horses without access to shade showed greater rectal temperature (RT), respiration rate (RR), and skin temperature (SK) and exhibited more sweat than horses that were completely shaded. Yet not known is whether horses will choose to stand in the shade when given a choice of areas with and without this resource. Our objective was to assess horse preference for shaded and unshaded areas in the hot and arid, sunny summer weather in Davis, California. For this preference test, 12 healthy, adult horses (6 mares, 6 geldings) were randomized into 3 sequential trials using 4 horses in each trial. The trials consisted of 2 d of acclimation and either 5 d (Trial 1) or 7 d (Trials 2 and 3) of observation. Horses were housed individually in dry lot pens. Half of each pen was covered by an open-sided shade structure. The amount of the pen shaded varied slightly throughout the day with a mean of 50.1% of the pen shaded. Physiological measurements (RT, RR, SK, sweat score) were recorded at 0900, 1230, and 1800 h. Behavioral observations (horses' location relative to shade, time spent walking, foraging, and standing) were recorded at 5-min intervals from 1300 to 1800 h daily and at 10-min intervals from 1800 to 1300 h on alternate days. Insect avoidance behavior was recorded for 1 min/h for each horse. Weather factors were recorded every 5 min, 24 h/d throughout the study; mean daytime ambient temperature was 29 °C ± 5 °C. Data were analyzed using PROC MIXED in SAS. Horses were located in the shade in 7.1% more observations than by chance (SE = 1.3, P < 0.001), with greatest use before and during peak solar radiation and then again following peak black globe temperature. Horses performed more walking and foraging behavior in the shaded areas (P < 0.01). Our research indicates that individually housed horses prefer shade when it is available in hot, sunny environments. These results support recommendations for access to shade when developing best practice guidelines for the care of domestic horses.