Abstract
ObjectiveThe aim of this study was to evaluate heat tolerance using heat tolerance indices, physiological, physical, thermographic, and hematological parameters in Santa Ines and Morada Nova sheep breeds in the Federal District, Brazil.MethodsTwenty-six adult hair sheep, one and a half years old, from two genetic groups (Santa Ines: 12 males and 4 females; Morada Nova: 7 males and 3 females) were used and data (rectal temperature, respiratory rate, heart rate, skin temperatures; hematological parameters) were collected during three consecutive days, twice a day (morning and afternoon), with a total of six repetitions. Also physical parameters (biometric measurements, skin and hair traits) and heat tolerance indices (temperature-humidity index, Iberia and Benezra) were evaluated. The analyses included analyses of variance, correlation, and principal components with a significance level of 5%.ResultsThe environmental indices, in general, indicate a situation of thermal discomfort for the animals during the afternoon. Breed significantly influenced (p<0.001) physiological and physical characteristics of skin, hair, biometric measurements and Iberia and Benezra heat tolerance indices. Santa Ines animals were bigger and had longer, greater number and darker hair, thicker skin, greater respiratory rate and Benezra index and lower Iberia index compared with Morada Nova breed.ConclusionAlthough both breeds can be considered adapted to the environmental conditions of the region, Morada Nova breed is most suitable for farming in the Midwest region. The positive correlation found between the thermographic temperatures and physiological parameters indicates that this technique can be used to evaluate thermal comfort. Also, it has the advantage that animals do not have to be handled, which favors animal welfare.
Highlights
The main environmental factors that affect livestock production are environmental temperature, humidity, solar radiation and wind speed [1]
High temperature-humidity index (THI) was observed in the afternoon, reaching values classified as danger and emergency [17], while in the morning the animals were in thermal comfort with mean and maximum THI of 59 and 61, respectively
Based on the scale proposed by Silanikove (2000), which qualifies the severity of heat stress according to breath rate, 37% of the animals in this experiment were under heat stress during the afternoon, of which 6.4% were suffered
Summary
The main environmental factors that affect livestock production are environmental temperature, humidity, solar radiation and wind speed [1]. Tropical regions, characterized by high levels of solar radiation and temperature, heat stress is a major factor limiting the development and production of animals [2,3]. The animal’s response to heat stress can be measured by variation in body temperature, respiratory and heart rate (HR), which tend to increase under thermal stress. This results in changes in hematological parameters as heat stress increases water and ion losses [4] as well as increasing plasma and extracellular volume [5]. One of the earliest index developed to evaluate thermal stress in animals was the Iberian heat tolerance test (HTC), which uses the rectal temperature (RT) as a variable. The aim of this study was to evaluate heat tolerance using heat tolerance indices, physiological, physical, thermographic and hematological parameters in Santa Ines (SI) and Morada Nova (MN) sheep breeds in the Federal District, Brazil
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