Abstract
Heat stress has been identified as a major cause of lower productive and reproductive performance in animal farming. Methods for protecting livestock from heat stress were investigated during the summer months, where one six Holstein cows kept under shade only (group 1), and another six cows kept under shade with evaporative cooling (group 2). The results show that shade and water sprayers (evaporative cooling) significantly lowered ambient temperature and thus reduced the heat stress experienced by dairy cows in Saudi Arabia. Evaporative cooling plus shade, lowered ambient temperature (41.80 ± 0.74 vs. 47.40 ± 0.84°C), increased relative humidity (0.33 ± 0.01 vs. 0.24 ± 0.01) and decreased the temperature humidity index (80.24 ± 0.60 vs. 84.77 ± 0.68) when compared to shade alone. In addition, cows kept under evaporative cooling (38.4 ± 0.32°C) experienced lower rectal temperatures compared to cows under shade alone (39.53 ± 0.44°C). Cows under evaporative cooling had higher serum concentrations of triidothyronine (2.50 ± 0.90 vs. 0.75 ± 0.20 ng/ml) and thyroxine (11.94 ± 1.60 vs. 7.22 ± 1.88) than cows under shade alone. Thus, evaporative cooling can decrease the heat stress experienced by dairy cows in Saudi Arabia and limit its associated detrimental effects.
Highlights
Desert environments have high daytime temperatures and solar radiation levels during the summer months [1]
temperature humidity index (THI) values of 70–72 units or less are considered acceptable [17], while a THI greater than 72 units causes a reduction in dry matter intake and milk production and composition manifested by having reduced fat, protein and casein contents in dairy cows [14, 25]
When rectal temperature reaches 39°C, high producing cows in early lactation show a sharp decline in milk production, since these cows are more susceptible to heat stress than low producing cows [32]
Summary
Desert environments have high daytime temperatures and solar radiation levels during the summer months [1]. Heat stress increases the rectal and core body temperatures of dairy cows [7, 8]. Increased body temperature reduces uterine blood flow [9, 10] leading to an increased uterine temperature, resulting in a decrease in fertility because of an unfavorable uterine environment for successful insemination. Blood concentrations of T3 and T4 are decreased in cows that are subjected to heat stress, since lowered thyroid hormone levels reduce heat production, which helps the body adapt to warmer environments [20]. The aim of this study was to use evaporative cooling to reduce the high environmental temperature, and its detrimental effects on rectal temperature and thyroid hormones in dairy Holstein cows in the semi-arid environment of the Riyadh region in Saudi Arabia
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