Anual variation of morphologic traits and hair coat surface temperature of Holstein cows in semi-arid environment

This work aimed to study the annual variation of temperature of the coat surface and other traits of coat in Holstein cows managed in a tropical environment by separately considering black coat and white coat. It was measured the coat thickness (mm) characteristic, hair length (mm), hair number (hair/cm(2)) and coat surface temperature on 191 crossbred cows with 7/8 and 31/32 Holstein composition distributed in 3 herds in a semi-arid environment. Less dense coats with shorter, flattened hair occurred predominantly in March, a time coinciding to high levels of solar radiation. This type of coat shows low resistance to the flux of latent and sensitive heat through the skin, thus favoring heat loss. The black coat surface temperature was on average 4 degrees C higher than that of the white one during all the year and its variation followed that of the mean radiant temperature. The models developed to predict the effective thermal conductivity of the coat must take these differences into account because the thermal gradient parallel to the skin surface is not negligible for Holstein cows under the sun in a tropical environment, as well as the other traits.