Preference of domestic horses for shade in a hot, sunny environment1

Abstract

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.

Macrolide‐induced hyperthermia in foals: Role of impaired sweat responses

“…In light of the presumed role of solar radiation in the heat stress seen in erythromycin‐treated foals kept outside, it was disappointing to find that shade structures did not prevent hyperthermia. In this regard, it should be noted that normal adult horses in a hot, sunny environment spent only 7.1% more time under shade than would have been expected by chance . If the dams in our study behaved likewise, foals might have tended to follow them into full sun even when at risk of hyperthermia, a behaviour we observed frequently during the study.…”

“…Dry-bulb ambient temperature is a convenient measure of environmental heat, but only reflects part of the total heat stress load in animals kept outside [11,13]. If precipitation and wind are not factors, dry-bulb ambient temperature and relative humidity, which are combined in the heat index to capture the extra heat stress of high humidity [10], are virtually identical whether measured under shade or in direct sunlight [13]. Exposure to direct solar radiation is the critical additional stressor during activity in full sun [13].…”

Clinical Approach to Commonly Encountered Problems

“…Changes in core body temperature and environmental temperature cause the sympathetic nervous system to regulate the degree of vasoconstriction and thus the amount of blood flow, with increases in temperature resulting in cutaneous vasodilation and increased skin blood flow. [6][7][8] Mechanisms that increase body temperature are triggered when the body temperature is too low. Evaporation is also an important mechanism of heat loss in horses.…”

24-h sheltering behaviour of individually kept horses during Swedish summer weather

“…Individually housed horses studied by Holcomb et al [ 4 ] used shade when given the choice during hot, sunny weather. Being in shade under a shelter structure increased feeding behaviour and locomotion and did not alleviate physiological changes that may have otherwise occurred in response to lack of shade [ 5 ].…”

“…Although shade, provided by a shelter with a roof and open on all four sides benefited horses in physiological terms, this shelter layout seemed insufficient to lower insect avoidance behaviour [ 4 , 5 ]. A shelter with closed sides may give better protection because it becomes more difficult for insects to visually locate the horse.…”