Latent heat loss of Holstein cows in a tropical environment: a prediction model

Alex Sandro Campos Maia,Roberto Gomes Da Silva,Cintia Maria Battiston Loureiro

doi:10.1590/s1516-35982008001000018

Alex Sandro Campos Maia, Roberto Gomes Da Silva + Show 1 more

Open Access

https://doi.org/10.1590/s1516-35982008001000018

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Abstract

Nine lactating Holstein cows with average 526 ± 5 kg of BW, five predominantly black and four predominantly white, bred in a tropical region and managed in open pasture were observed to measure cutaneous and respiratory evaporation rates under different environmental conditions. Cows were separated in three weight class: 1 (<450 kg), 2 (450-500 kg) and 3 (>500 kg). Latent heat loss from cutaneous surface was measured using a ventilated capsule; evaporation in the respiratory system was measured using a facial mask. The results showed that heaviest cows (2 and 3 classes) presented the least evaporation rates. When air temperature increased from 10 to 36ºC the relative humidity decreased from 90 to 30%. In these conditions the heat loss by respiratory evaporation increased from 5 to 57 Wm-2, while the heat loss by cutaneous evaporation increased from 30 to 350 Wm-2. The results confirm that latent heat loss was the main way of thermal energy elimination under high air temperatures (>30ºC); cutaneous evaporation was the main mechanism of heat loss, responding for about 85% of the heat loss. A model was presented for the prediction of the latent heat loss that was based on physiological and environmental variables and could be used to estimate the contribution of evaporation to thermoregulation; a second, based on air temperature only, should be used to make a simple characterization of the evaporation process.

Highlights

Thermal equilibrium is achieved by cattle when the amount of heat produced by metabolic reactions equals the heat gained by the body from the environment
Knowledge about the latent heat flow from Holstein cows managed under natural conditions in a tropical environment would contribute to genetic improvement programmes of dairy cattle in the tropics, by including fitness characteristics that are more favourable to the heat balance of animals
In Holstein cows managed in tropical environment the dissipation of latent heat by evaporation is the main way of elimination of excess thermal energy, when air temperature exceeds 30oC

Summary

Introduction

Thermal equilibrium is achieved by cattle when the amount of heat produced by metabolic reactions equals the heat gained by the body from the environment. Under high temperatures the body can gain heat by convection (Gebremedhin & Binxin, 2001); if the environment is characterized by intense solar radiation the body gains large amounts of heat by radiation (Curtis, 1982). In those conditions the ability of the animal to withstand its environment is proportional to its ability to dissipate heat by evaporation from the skin surface as a result of sweating (Finch et al, 1982; McLean, 1963; Maia et al, 2005a) or from the respiratory system by panting (Stevens 1981; Maia et al, 2005b). Knowledge about latent heat loss mechanisms can be used to develop mathematical and physical models as those proposed by Stevens (1981), McLean (1963), Gebremedhin et al (1981), Turnpenny et al (2000) and McGovern & Bruce (2000) to explain thermal interaction between livestock and their environment

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