Applying Reflective Pigment to the Dorsal Surface of Cattle to Reduce Heating by Sunlight
By Elsie J. McCoy and Steve J. Bartle
Heat stress in feedlot cattle has serious animal welfare and economic implications. Documented feedlot cattle losses have exceeded 5,000 head in seven of the last 20 years, and non-death costs are estimated at five to 10 times greater than death losses (Mader, 2014). Environmental conditions including ambient temperature, humidity, wind, and solar radiation can affect heat load. Also, 75 to 77% of domestic beef cattle are black colored (Corah, 2016). The environmental and animal factors are difficult to control, especially in a cost effective manner. However, heat absorbed from solar radiation is addressed in nature through light colored hides and in buildings with white roofs. A question was asked – Would a reflective pigment on the hair coat reflect solar energy and help mitigate heat stress in colored feedlot cattle? The pigment titanium dioxide is highly reflective and chemically inert (Dupont, 2007). It is approved for use in feeds, food coloring, and sunscreens. The objective of this experiment was to determine if titanium oxide coatings reflect solar radiation from cattle and mitigate heat stress. Feedlot heifers (n = 30, 29 black and 1 red; 591 lb +/- 60.8 lb) were used to evaluate a reflective coating containing titanium dioxide. Heifers were randomly assigned to control or coated treatments. The coating was applied to the dorsal midline with an electronic airless sprayer except for the area over the shoulders, which served as a control. Vaginal thermometers attached to blank CIDRs were inserted into six heifers in each treatment to continuously record internal body temperature. Coatings and thermometers were applied from 10:00 to 11:00 am on a day with a high ambient temperature of 101° F and a temperature humidity index of 87.8. Starting at about 1:00 pm, reflectance surface in the major color zones from the dorsal were measured with a suspended modified digital camera. Hide surface temperature was measured with a suspended infrared thermal imaging sensor; adjacent panels of white, black, and grey provided reference temperatures. A sprinkler was turned on at about 2:30 pm because of severe heat stress in several cattle. Reflectance and hide surface temperature were compared between two areas of the same animal. Reflectance in the blue, green, and red color zones was found to be 5.7, 8.8, and 10.3 times greater (P < 0.001), respectively, for the coated areas (back) than the uncoated (shoulder) areas. Dorsal surface temperature averaged 102.3 and 108.3° F for coated and uncoated areas, respectively (P < 0.001). When a light wave strikes a surface, it can pass through, be reflected away from the surface, or be absorbed and converted to heat. As the amount of light that is reflected increases, the amount absorbed decreases. Reflectance values and hide surface temperatures suggest that solar energy was reflected rather than absorbed. Body temperatures were compared between coated and uncoated animals. Uncoated cattle had a 1.6° F greater (Fig.2; P < 0.01) body temperature increase than coated cattle over a two to three hour exposure to natural solar radiation, which suggests that heat stress was reduced in coated cattle. A reflective coating applied to the dorsal midline of feedlot cattle shows potential to decrease heat absorbed and reduce heat stress.
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