Historical evolution of productive indicators in dairy cows in grazing systems

Abstract

We used retrospective data corresponding to the lactations of 300 primiparous and multiparous Holstein cows, collected between 1992-2012 in farm located in Casilda, province of Santa Fe-Argentina. The animals were divided into two groups: pure cows (VP, n = 120) and cows with breeding registers (VRC, n = 180). The dispersion diagrams resulting from jointly representing the values of the milk index (Y) and the total milk production (X), corresponding to each individual, were prepared ?rst. Dispersion diagrams were made linking the same indicators, but restricting the association to pure cows and with breeding registers, within each category (low, medium and high) of production. For pure cows: low production cows: r = 0.883; P <0.0001; cows of intermediate production: r = 0.577; P <0.0001 and high production cows: r = 0.391; P = 0.0139.For the cows breeding record: low production cows: r = 0.739; P <0.0001; cowsofintermediateproduction:r=0.691;P<0.0001andhighproductioncows:r=0.568;P<0.0001.Theslopeswere positive and signi?cant. A decrease in the value of the slope (P <0.0001) was observed together with an increase in the residual variance with the increase in milk production. It is concluded that in addition to the total liters of milk, the contribution of other variables such as longevity, ef?ciency in breeding and reproductive ef?ciency should be incorporated.