Effect of extreme severe heat stress on respiratory rate in unshorn and shorn Australian Merino rams from Northern Patagonia

Abstract

The aim of this study was to determine the effects of severe extreme thermal stress on the respiratory rate (panting) of unsheared and sheared rams in standing and lying position, and to analyse two temperature-humidity indices (THIs). Six mature Australian Merino rams from Northern Patagonia, three unshorn and three shorn, were subjected to 40 hours (8 hours each day for five days) of gradual increase in temperature from 25°C to 40°C, guaranteeing 4h daily at 40°C in a heat chamber. Respiratory rate (RR) was registered continuously by counting flank movements, and the ambient air temperature and relative humidity were recorded every five minutes inside the heat chamber. From 1413 RR measurements, descriptive and modelling analyses were performed. Panting as a response variable was distributed into five categories, and fixed effects such as THI, wool (unshorn/shorn), and position (standing/lying) were considered. No significant differences were observed between the panting score in the unshorn (standing or lying) and standing (unshorn or shorn) sheep, but significant differences were observed in shorn and lying rams. The explanations could be that heat production from muscle activity was lower and the transfer and heat lost by conduction to the floor was easier in the rams with shorter fleece (at least 0.7 inches long). However, in the unshorn rams, their wool acted as an insulator, both with air as well as the floor. Australian Merino rams from Northern Patagonia are heat tolerant to an environment between 31.5°C and 42°C, and 32% to 48% humidity for 40 hours over five days. The rams were in the first phase of panting, and the normal rectal temperatures registered daily when leaving the heat chamber confirmed that regulation of body temperature was possible. The LPHSI's THI was adjusted to improve the analysis of the RR more than the National Research Council's THI. Keywords: Australian Merino rams. Heat stress. Respiratory rate. Unshorn / shorn. Standing / lying down. ResumoO objetivo deste estudo foi determinar o efeito do estresse térmico extremamente severo sobre a frequência respiratória (ofego) em carneiros com lã e tosquiados, em pé ou deitados, e analisar dois índices de temperatura e umidade (ITU). Seis carneiros Merino Australiano da Patagônia Norte, três com lã e três tosquiados, foram expostos durante 40 horas a aumento gradual de temperatura de 25 a 40°C (oito horas durante cinco dias), garantindo quatro horas diárias a 40°C em uma câmara de calor. A frequência respiratória foi registrada continuamente mediante a contagem dos movimentos do flanco. A temperatura e a umidade relativa ambiente foram registradas a cada cinco minutos dentro da câmara. A partir de 1.413 frequências respiratórias registradas, uma análise descritiva foi realizada e um modelo calculado. A variável de resposta do ofego foi dividida em cinco categorias e os efeitos fixos considerados foram: ITU, lã (com lã ou tosquiado) e posição (em pé ou deitado). Não se observaram diferenças significativas nas frequências de ofego ...

Características Termorreguladoras De Ovinos Da Raça Dorper Criados Em Condições Climáticas De Meio-Norte Do Brasil / Thermoregulatory Characteristics of Dorper Sheep Reared in Climatic Conditions in the Mid-North Region of Brazil

“…Médias dos parâmetros fisiológicos, frequência respiratória (FR) e cardíaca (FC), temperatura retal (TR) e temperatura superficial média (TSM), de ovinos da raça Dorper criados em condições climáticas do Meio-Norte do Brasil. Autores como Gottardi et al (2018), López Armengol et al (2017 e Lima et al (2018) afirmaram que as variáveis climáticas podem proporcionar situações de estresse térmico aos animais, mas esse fato não é interessante do ponto de vista produtivo e reprodutivo, haja vista que a energia obtida com a alimentação será direcionada para a maior ativação dos mecanismos de termorregulação, na tentativa dos animais em manter a homeostase de todo o seu organismo, em detrimento da energia que seria destinado a produção.…”

Large-Scale Phenotyping of Livestock Welfare in Commercial Production Systems: A New Frontier in Animal Breeding

“…In general, animals cope with heat stress by increasing RR to reduce the extra heat load via evaporative heat loss. However, it is important to mention that during extreme heat strain when heat loss cannot be balanced with heat gain, animals will switch from increased RR to deep slow respirations (López Armengol et al, 2017). One way to measure RR is visually by counting flank movements at the flank region (Mostaço et al, 2015).…”