Physiological traits as affected by heat stress in sheep—A review

Thirty Santa Ines adult, non-lactating, non-pregnant ewes, ten with a brown coat, ten black coated and ten white coated, as well as ten Bergamasca and ten of mixed breed were used to evaluate the effect of climate on physiological and blood parameters in sheep. Two sample collections were taken (6 am and 2 pm) on six days. Sweating rate (SR), heart (HR) and breathing rates (BR), complete hemogram, rectal (RT) and skin temperatures (ST) were measured. Variance analyses were carried out using SAS®. In general, there were significant differences between animals due to skin type, time and day of collection. White coated animals showed lower HR, BR and RT, with afternoon parameters higher than morning. Correlations between HR, BR, RT, SR and ST were medium and positive. Correlations between physiological and blood traits were in general negative and medium. Packed Cell Volume (PCV), total plasma proteins, red blood cell count and hemoglobin concentration had high positive correlations between each other. The first two autovectors explained 49% of variation between traits. White coated Santa Ines animals were shown to be better adapted to climatic conditions in Central Brazil and wool sheep more affected by heat.

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Heat tolerance in Brazilian sheep: physiological and blood parameters.

Appropriate thyroid gland function and thyroid hormone activity are considered crucial to sustain the productive performance in domestic animals (growth, milk or hair fibre production). Changes of blood thyroid hormone concentrations are an indirect measure of the changes in thyroid gland activity and circulating thyroid hormones can be considered as indicators of the metabolic and nutritional status of the animals. Thyroid hormones play a pivotal role in the mechanisms permitting the animals to live and breed in the surrounding environment. Variations in hormone bioactivity allow the animals to adapt their metabolic balance to different environmental conditions, changes in nutrient requirements and availability, and to homeorhetic changes during different physiological stages. This is particularly important in the free-ranging and grazing animals, such as traditionally reared small ruminants, whose main physiological functions (feed intake, reproduction, hair growth) are markedly seasonal. Many investigations dealt with the involvement of thyroid hormones in the expression of endogenous seasonal rhythms, such as reproduction and hair growth cycles in fibre-producing (wool, mohair, cashmere) sheep and goats. Important knowledge about the pattern of thyroid hormone metabolism and their role in ontogenetic development has been obtained from studies in the ovine foetus and in the newborn. Many endogenous (breed, age, gender, physiological state) and environmental factors (climate, season, with a primary role of nutrition) are able to affect thyroid activity and hormone concentrations in blood, acting at the level of hypothalamus, pituitary and/or thyroid gland, as well as on peripheral monodeiodination. Knowledge on such topics mirror physiological changes and possibly allows the monitoring and manipulation of thyroid physiology, in order to improve animal health, welfare and production.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/4FFE9A3AF1BBAD021CF18F1830FFD6C9/S1751731107000262a.pdf/div-class-title-thyroid-hormones-in-small-ruminants-effects-of-endogenous-environmental-and-nutritional-factors-div.pdf

Thyroid hormones in small ruminants: effects of endogenous, environmental and nutritional factors.

The thermal environment is the most important ecological factor determining the growth, development, and productivity of domestic animals. Routes of energy exchange (sensible heat and latent heat) between animals and their environment are greatly influenced by body weight, fat deposition, hair-coat properties, functional activity, and number of sweat glands, as well as the presence or absence of anatomical respiratory countercurrent heat exchange capability. Differences in these anatomical features across species have led to specialization of heat exchange. Thermal plasticity and degree of acclimation are critical factors determining the ability of animals to respond to environmental change. Increases in productive capability of domestic animals can compromise thermal acclimation and plasticity, requiring greater investments in housing systems that reduce variability of the thermal environment. The combination of steadily increasing metabolic heat production as domestic animal productivity increases and a rising world temperature poses ongoing and future challenges to maintaining health and well-being of domestic animals.

Thermal Biology of Domestic Animals

The livestock sector is socially, culturally and politically very significant It accounts for 40% of the world's agriculture Gross Domestic Product (GDP) It employs 13 billion people, and creates livelihoods for one billion of the world's population living in poverty Climate change is seen as a major threat to the sur- vival of many species, ecosystems and the financial sustainability of livestock production systems in many parts of the world The potential problems are even greater in developing countries Economic studies suggest severe losses if current management systems are not modified to reflect the shift in climate In short, farmers/ managers need to adapt to the changes There has been considerable interest in gaining an understanding how domestic livestock respond to climatic stressors Studies have for the most part been undertaken in developed coun- tries These studies have provided a wealth of knowledge on differences between genotypes, the impact of climatic stress on production, reproduction and health However little is known about adaptation of animals to rapid changes in climatic

Response of Domestic Animals to Climate Challenges

The variation of cortisol and thyroid hormones in Corriedale sheep bred in a tropical environment was evaluated. Fourteen males and seven females were observed in a climatic chamber at 45oC for nine days, eight hours per day. Rectal temperature (TR), respiratory rate (FR), air temperature (TA) and air humidity (PV) were recorded. The animals were ranked according to their responses for TR and FR and then the five highest (A group) and five lowest (NA group) ranked animals were selected. These ten animals were moved to a pen where they were observed along one year for TR and FR two times a day, and blood-sampled once a week. The results showed differences for T3, T4, and cortisol concentrations, which were attributed to variations in TA and PV. Cortisol concentrations were higher and T3 and T4 ones were lower under increased TA and PV. Correlations of TA and PV with cortisol values were r = .224 and r = .395 respectively. The negative correlations of TA with T3 (r = -.151) and T4 (r = -.156) showed that increase in TA may be followed by decrease in the metabolic rate. No significant difference for all variables investigated was found between the two groups, thus it is not recommended the use of TR and FR as the only criteria to evaluate sheep performance in tropical environments.

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Variação estacional dos hormônios tireoideanos e do cortisol em ovinos em ambiente tropical

- Ten adult Corriedale sheep were evaluated for respiratory ( E R ) and cutaneous ( E C ) evaporation rates. The animalswere observed about 10 times each by recording changes in their live weigth with high-sensitiviy strain gauges, under different conditions of airtemperature (21.1 to 41.9 o C) and partial vapour pressure (1.53 to 3.01 kPa). Average evaporation rates were 0.7599±0.0094 g.h -1 .kg -1 for E R and 1.3029 ±0.0591 g.h -1 .kg -1 for E C . Cutaneous evaporation was considered as an important heat loss mechanism for sheep in hotenvironments. There were discussed the effects of sex, fleece thickness, air temperature, and air humidity.Key Words: cutaneous evaporation, heat loss, respiratory evaporation, sheep 1 Professor Titular, Departamento de Zootecnia, Faculdade de Ciencias Agrarias e Veterinarias, UNESP. 14884-900 Jaboticabal, SP. E-mail: rgomes@fcav.unesp.br 2 Professora Assistente Doutora, Faculdade de Veterinaria, Universidade de Franca, Franca, SP. E.mail: barbante@fcav.unesp.br

https://www.scielo.br/pdf/rbz/v32n6s2/20968.pdf

Evaporação cutânea e respiratória em ovinos sob altas temperaturas ambientes

It was investigated the rectal temperature, respiratory frequency and total evaporative heat loss rate in Corriedale sheep under three air temperatures, aiming a better comprehension of thermoregulation mechanisms of these animals. Initially, 21 adult animals were housed in climatic chamber under 45oC and variable air humidity (PV), recording the respiratory frequency (FR) and rectal temperature (TR). Basing on the FR and TR, it was selected 10 animals, five of the lowest values, assuming as being the best heat adapted (group 1) and five of the highest values, assuming as the worst heat adapted (group 2). The selected animals were maintained in climatic chamber, where it was measured again TR, FR and total evaporation rate (TET), under 20, 30 and 40oC of air temperature and variable PV. There was no statistical difference between the classified groups, for all the measured variables. In conclusion, the use of the physiological variables TR and FR as mainly parameters for these animals selection, is not enough for evaluate the level of adaptation under high temperatures.

/pdf/analise-de-algumas-variaveis-fisiologicas-para-avaliacao-do-17fcvz8zcq.pdf

Análise de algumas variáveis fisiológicas para avaliação do grau de adaptação de ovinos submetidos ao estresse por calor

Estudou-se a influencia de fatores climaticos sobre as respostas fisiologicas de bezerros, puros e cruzados, filhos de vacas da raca Nelore ou de alta mesticagem de Nelore acasaladas com touros das racas Aberdeen Angus (AN), Simental (SN), Canchim (CN) e Nelore (NI e NR). Os bezerros AN, SN, CN e NI foram mantidos em sistema rotacionado intensivo, enquanto o grupo NR foi mantido em sistema extensivo. Os bezerros foram observados de forma direta desde o nascimento ate a primeira mamada, medindo-se a latencia para a primeira mamada (LM). Aproximadamente 24 horas apos o parto, coletaram-se amostras de sangue do bezerro para as dosagens de proteina total (PT), glicose (Gli), triiodotironina (T3), tiroxina (T4), relacao T4:T3, cortisol (Cort) e imunoglobulina G (IgGb), alem das medidas de temperatura retal do bezerro (TR) e dos pesos de vacas e bezerros. Para analise dos efeitos de clima, foram tomadas no dia do nascimento as medidas de temperatura do ar (Temp), umidade do ar (UR) e precipitacao (PRE). Os parâmetros fisiologicos foram estudados pelo metodo dos quadrados minimos com modelos que incluiram os efeitos de ano e mes de nascimento, grupo e sexo do bezerro, categoria da vaca e hora do parto e das interacoes ano × grupo e ano × mes de nascimento, alem das covariaveis peso do bezerro, PRE, Temp, UR e LM. Temp mostrou efeito significativo para as concentracoes de T3, T4, T4:T3 e de Cort. Quanto maior Temp, menores as concentracoes de T3 e de Cort e maiores as de T4 e de T4:T3. LM influenciou os niveis de Cort, PT e IgGb, de modo que, quanto maior LM, maior a concentracao de Cort e menor as de IgGb e PT. Tambem houve efeito significativo de grupo do bezerro sobre PT, que foi maior nos bezerros NR que nos bezerros NI.

https://www.rbz.org.br/wp-content/uploads/articles_xml/1516-3598-rbz-S1516-35982006000400028/1516-3598-rbz-S1516-35982006000400028.pdf

Josiane Maria Cardoso Starling

Papers

Variação estacional dos hormônios tireoideanos e do cortisol em ovinos em ambiente tropical

Evaporação cutânea e respiratória em ovinos sob altas temperaturas ambientes

Análise de algumas variáveis fisiológicas para avaliação do grau de adaptação de ovinos submetidos ao estresse por calor

Avaliação das respostas fisiológicas de bezerros zebuínos puros e cruzados nascidos em clima subtropical