Latent heat loss of dairy cows in an equatorial semi-arid environment

Abstract

The present study aimed to evaluate evaporative heat transfer of dairy cows bred in a hot semi-arid environment. Cutaneous (E(S)) and respiratory (E(R)) evaporation were measured (810 observations) in 177 purebred and crossbred Holstein cows from five herds located in the equatorial semi-arid region, and one herd in the subtropical region of Brazil. Rectal temperature (T(R)), hair coat surface temperature (T(S)) and respiratory rate (F(R)) were also measured. Observations were made in the subtropical region from August to December, and in the semi-arid region from April to July. Measurements were done from 1100 to 1600 hours, after cows remained in a pen exposed to the sun. Environmental variables measured in the same locations as the animals were black globe temperature (T(G)), air temperature (T(A)), wind speed (U), and partial air vapour pressure (P(V)). Data were analysed by mixed models, using the least squares method. Results showed that average E(S) and E(R) were higher in the semi-arid region (117.2 W m(-2) and 44.0 W m(-2), respectively) than in the subtropical region (85.2 W m(-2) and 30.2 W m(-2), respectively). Herds and individual cows were significant effects (P < 0.01) for all traits in the semi-arid region. Body parts did not affect T(S) and E(S) in the subtropical region, but was a significant effect (P < 0.01) in the semi-arid region. The average flank T(S) (42.8°C) was higher than that of the neck and hindquarters (39.8°C and 41.6°C, respectively). Average E(S) was higher in the neck (133.3 W m(-2)) than in the flank (116.2 W m(-2)) and hindquarters (98.6 W m(-2)). Coat colour affected significantly both T(S) and E(S) (P < 0.01). Black coats had higher T(S) and E(S) in the semi-arid region (41.7°C and 117.2 W m(-2), respectively) than white coats (37.2°C and 106.7 W m(-2), respectively). Rectal temperatures were almost the same in both subtropical and semi-arid regions. The results highlight the need for improved management methods specific for semi-arid regions.

Evaluation of Physiological Responses of Calves During Rainy Season in the Semiarid Environment

“…Probably the sweating rate of the studied calves has been raised. The sweating rate in dairy cows in semi-arid environment corresponds to 72.7% of the total evaporative heat loss (Silva et al, 2012).…”

Thermoregulatory responses of sindhi and guzerat heifers under shade in a tropical environment

“…It was directed perpendicular to the animals' surface at a distance of 20 cm from the following regions: the head, the back, the shin, and the udder. The T s value was determined according to the equation in Pinheiro et al (2005): T s = 0.1·T head + 0.7·T back + 0.12·T shin + 0.08·T udder Mathematical models developed by Maia et al (2005b) and Silva et al (2012) were used in order to estimate latent heat flux through the respiratory tract:…”

“…The absolute humidity of the expired air (Ψ EXP ) was calculated according to the following equations developed by Silva et al (2012) and Maia et al (2005b): In order to estimate the heat loss by cutaneous evaporation, the exponential model developed by Silva and Maia (2011) as a function of the animal's surface temperature (T S ) was used: E c = 31.5 + 3.67e…”

“…Cattle heat loss by evaporation occurs mainly at the epidermis and, accounts for approximately 80% of the total loss under heat stress conditions (MCLEAN, 1963;FINCH, 1985;MAIA et al, 2005a;SILVA et al, 2012).…”

“…Some researchers have developed mathematical models that use indirect measures such as respiratory rate and surface temperature to predict latent heat flow in cattle (MAIA et al, 2005b;MAIA, 2011;SILVA et al, 2012). These studies showed that heat loss by cutaneous evaporation is determined by surface temperature and, latent heat loss through the respiratory tract is based on the respiratory rate and the relationship between the vapor pressure of inspired and expired air.…”