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

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