Les besoins en eau d'abreuvement des bovins laitiers : déterminismes physiologiques et quantification

Drinking water is an incompressible need of dairy farms. It represents a significant cost and, an immediate consequence of its restriction is a decrease in milk yield and an alteration of animal welfare. Animal water balance is maintained thanks to regulation of renal excretion of water and thirst in responses to set points related to plasmatic osmotic pressure and blood volume. Numerous predictive equations for water requirements of dairy cows have been published. Diet dry matter content is the first determinant of drinking water volume because it determines the relative part of feed water and drinking water in the total amount of water intake. Dry matter intake, diet contents of sodium, potassium and nitrogen and ambient temperature are the main determinants of total water intake. The comparison of the prediction error of the predictive equations on a common data set showed contrasted performances. The choice of an equation should be based on the nature of the available predictors and the conditions in which it was established. Given that most of the predictive equations for dairy cow water requirements are established from individual measurements, their application to a herd watered through constant trough level requires adjustments. Some elements are also given in the paper to predict the water requirements of heifers.