The specific enthalpy of air as an indicator of heat stress in livestock animals

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The specific enthalpy of air as an indicator of heat stress in livestock animals Sérgio Luis de Castro Júnior 1

&

Iran José Oliveira da Silva 1

Received: 4 May 2020 / Revised: 16 September 2020 / Accepted: 16 September 2020 # ISB 2020

Abstract Along with recognition of environmental effects on the performance and welfare of livestock animals, studies have been proposing new methodologies and parameters to diagnose the heat stress of animals through the physical properties of air. This article aims to present the state-of-the-art on the use of the specific enthalpy of air as an indicator of heat stress in livestock animals. As a starting point, conceptual considerations were made about the connection between homoeothermic animals and the environment. Variables for heat stress evaluation based on psychrometric air properties are then described, including dry bulb temperature and relative humidity, which are often used microclimate variables, and the specific enthalpy of dry air, which acts as a thermal comfort index. Final considerations highlight the recent history of the use of specific enthalpy of air equations as indicators of heat stress in livestock animals, with the intention of better understanding the relationship between animals and the environment. As a conclusion, the specific enthalpy of air is recommended as an indicator in the assessment of livestock housing conditions as, unlike other indices, it is based on thermodynamic air properties and not on linear regressions. Keywords Thermoregulation . Specific enthalpy of air . Livestock housing . Livestock bioclimatology . Thermal comfort index

Introduction In livestock production, one of the major problems that affect both small and big farmers is the effect of the thermal environment on the welfare and zootechnical performance of animals (Bloemhof et al. 2013). This concern, shared by the vast majority of livestock species’ breeders, is exponential in countries under tropical and subtropical climates—such as Brazil— where high temperatures during a long period of the year are common. In addition, the effects of climate change on livestock production over the next years have become a major point of concern (Rojas-Downing et al. 2017; Rashamol et al. 2018). Even indoors, where farm animals are protected from weather conditions, thermal problems are common due to * Sérgio Luis de Castro Júnior [email protected] Iran José Oliveira da Silva [email protected] 1

Livestock-Environment Research Group (NUPEA), Department of Biosystems Engineering (LEB), Luiz de Queiroz College of Agriculture (ESALQ), University of São Paulo (USP), Av. Pádua Dias, 11, Piracicaba, SP 13418-900, Brazil

the high density of livestock, misuse of natural resources (such as the sun and wind), and other factors that directly influence animal metabolism and the heat exchanged between animals and their environment (Mathur and Horst 1994). Thus, the management of livestock animals in hot climates is a challenge. In the short term, the physiological and behavioral chan

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