Evaluation of some methods for the measurement of respiratory and skin surface evaporation in cattle and other animals

Abstract

Skin surface evaporation (ES) accounts for about 80% of the thermal energy losses by cattle in hot environments. However, the relative efficiency of the several methods used to determine ES is not clearly established. Direct evaluation of water losses through the body weight differential within a given time interval can be considered as the most confident technique, but it requires costly high precision scales and involves a lot of careful work; hence, it is not useful for field studies involving many animals. Present study aims to evaluate the relative efficiency of three methods for measurement of skin surface evaporation: colourimetric method, ventilated capsule, and a commercial device (VapoMeter). Each one of ten Holstein cows will be weighed on a precision scale (600 kg capacity, 10g readability) by considering two treatments (exposure to direct sunlight and under shade), with three repetitions per cow per treatment. Just after weighing, each animal was measured for ES by the three methods successively. The total amount of evaporated water is estimated by the difference in body weight measured with a 30-minute interval, from which it was subtracted the amount of eliminated urine and faeces. The respiratory evaporation indirectly obtained from the respiratory rate, the temperature of the expired air and the tidal volume, is subtracted from the total evaporated water, in order to obtain the standard ES value. This standard ES value will be compared to the respective ones obtained by the three methods. The data will be analysed by least squares methods, considering a model like that y_ijkl=m + m_i+t_j+a_k+(mt)_ij+ e_ijkl, where mi = effect of the ith method(I =1,&,4), tj = effect of the jth treatment (j=1,2), ak = effect of the kth animal (k = 1,&,10), (mt)ij = effect of the interaction of ith method with jth treatment. (AU)