Abstract
The objective of this study was to compare physiological and thermographic responses to heat stress in three breeds of cattle. Fifteen animals of each of the Nelore, Pantaneiro and Curraleiro Pe-Duro breeds, of approximately two years of age, were evaluated. Heart and respiratory rates, rectal and surface temperature of animals as well as soil temperature were recorded at 8:30 and 15:30 on six days. Variance, correlation, principal factors and canonical analyses were carried out. There were significant differences in the rectal temperature, heart and respiratory rate between breeds (p < 0.001). Nelore and Pantaneiro breeds had the highest rectal temperatures and the lowest respiratory rate (p < 0.001). Breed was also significant for surface temperatures (p < 0.05) showing that this factor significantly affected the response of the animal to heat tolerance in different ways. The Curraleiro Pe-Duro breed had the lowest surface temperatures independent of the period evaluated, with fewer animals that suffered with the climatic conditions, so this may be considered the best adapted when heat challenged under the experimental conditions. Thermography data showed a good correlation with the physiological indexes, and body area, neck and rump were the main points.
Highlights
The high temperatures and low humidity during the dry season found in mid-west Brazil directly affect animal production and increased the susceptibility of animal diseases [1,2]
Animals can suffer heat stress when the temperature is higher or lower than the thermal comfort zone [21], and according to Nienabar & Hahn [22], night-time cooling is fundamental for an animal to maintain production under heat stress
The use of infrared thermography can assist in identifying the thermal stress of the animals
Summary
The high temperatures and low humidity during the dry season found in mid-west Brazil directly affect animal production and increased the susceptibility of animal diseases [1,2]. Excessive heat causes decreased food intake and disturbances in protein and energy metabolism, mineral balance, enzymatic reactions, and hormones’ and metabolites’ secretion in the blood [3,4]. All these factors negatively affect production, causing economic losses for the farmer. Adapted animals are characterized by the ability to survive in extreme environmental and climatic conditions. These animals maintain or show a minimal reduction in productive performance exhibiting high reproductive efficiency, disease resistance, longevity and low mortality rate during the exposure to stress [7]
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