Shade use by small groups of domestic horses in a hot, sunny environment

Horses in the United States are commonly managed in outside pens or pastures in small groups. Limited research on shade use by domestic horses housed singly in individual pens has shown benefits and a preference for using available shade. The objective of this study was to examine the amount of shade use and the behavioral and physiological responses of small groups of horses when housed with access to shade (SH) and without access to shade (SUN). Thirty-six horses were randomized into 3 consecutive trials using 3 horses per group and 4 groups per trial. Groups experienced 5 d in each treatment in a crossover design. Weather factors were measured with automated sensors 24 h/d throughout the study. The mean afternoon ambient temperature was 31.0°C with relative humidity of 32%. Rectal temperature, respiration rate, and skin temperature were recorded at 1000, 1330, and 1900 h daily. Venous blood samples were obtained on Days 0 and 5 to measure serum cortisol, the neutrophil:lymphocyte ratio, and hematocrit. Behavioral observations for presence in shade, standing near or away from water, locomotion, and foraging were recorded at 5-min intervals from 1400 to 1900 h daily. Insect avoidance behaviors were recorded hourly during that same time period for 1 min/horse. Horses in the SH treatment were observed using shade in 7.1% of observations between 1400 and 1900 h, and behavioral differences were observed between the SH and SUN treatments. When in the SUN treatment, horses stood near the water troughs more (18.5 vs. 14.2% of observations; = 0.029) and foraged less (29.3 vs. 33.8% of observations; < 0.001) than when in the SH treatment. There were no treatment differences for other behaviors or for physiological measures ( > 0.05). Provision of shade structures accessible to groups of mature, healthy horses in hot, sunny environments should be considered in developing future guidelines for best management practices for horses.