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

  • María Fernanda López Armengol Universidad Nacional del Comahue, Facultad de Ciencias Agrarias, Laboratorio de Teriogenología “Dr. Héctor H. Morello” Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Centro de Investigaciones en Toxicología Ambiental y Agrobiotecnología del Comahue (CITAAC) http://orcid.org/0000-0002-5437-6885
  • Ronina Paola Freund Universidad Nacional del Comahue, Facultad de Ciencias Agrarias, Laboratorio de Teriogenología “Dr. Héctor H. Morello”
  • Gustavo Néstor Giménez Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Centro de Investigaciones en Toxicología Ambiental y Agrobiotecnología del Comahue (CITAAC) Universidad Nacional del Comahue, Facultad de Economía y Administración, Departamento de Estadística
  • Natalia Rubio Universidad Nacional del Comahue, Facultad de Economía y Administración, Departamento de Estadística
Keywords: Australian Merino rams, Heat stress, Respiratory rate, Unshorn / shorn, Standing / lying down

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.

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Author Biographies

María Fernanda López Armengol, Universidad Nacional del Comahue, Facultad de Ciencias Agrarias, Laboratorio de Teriogenología “Dr. Héctor H. Morello” Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Centro de Investigaciones en Toxicología Ambiental y Agrobiotecnología del Comahue (CITAAC)

Producción Animal

Laboratorio de Teriogenología

Ronina Paola Freund, Universidad Nacional del Comahue, Facultad de Ciencias Agrarias, Laboratorio de Teriogenología “Dr. Héctor H. Morello”
Laboratorio de Teriogenología
Gustavo Néstor Giménez, Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Centro de Investigaciones en Toxicología Ambiental y Agrobiotecnología del Comahue (CITAAC) Universidad Nacional del Comahue, Facultad de Economía y Administración, Departamento de Estadística
Departamento de Estadística
Natalia Rubio, Universidad Nacional del Comahue, Facultad de Economía y Administración, Departamento de Estadística
Departamento de Estadística
Published
2017-05-19
How to Cite
López Armengol, M., Freund, R., Giménez, G., & Rubio, N. (2017). Effect of extreme severe heat stress on respiratory rate in unshorn and shorn Australian Merino rams from Northern Patagonia. Brazilian Journal of Veterinary Research and Animal Science, 54(1), 36-47. https://doi.org/10.11606/issn.1678-4456.bjvras.2017.108524
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