An economic model, to farm level, was developed to study the annual profitability per cow in the dairy farms of the Basque Country and Navarre. The model allows the calculation of the economic weights (PE) of three productive traits (milk volume, milk fat and milk protein) and two functional traits (cow's mature body weight and longevity) which appear in the model.
Information from cows in herds of the Basque Country and Navarre, who were in the Dairy Recording Scheme from 1979 to 2000, and having notes of conformation traits were used in the study. Records relative to the year 1995 were taken to calculate the economic weights, and the cows mature body weight (PA) was calculated from the note of the Size conformation trait.
Energy intake requirements of animals were estimated following two different evaluation norms, which produced similar results for the PE of the traits studied.
The PE obtained for mature body weight was -76.54 pts./kg·cow·year (-0.46 eur./kg·cow·year). This value was, in relative terms, the 13 per cent of that for milk protein, and resulted fearly close to that of milk volume, who was the 16 per cent of that for protein.
It seems evident that the inclusion of mature body weight in an economic selection index would improve the dairy farm profit ability, by means of a control of the increase in the cows body weight seen to be produced in the population during the analized period, and linked to its increase in milk production.