Historical evolution of productive indicators in dairy cows in grazing systems

Abstract

Retrospective data corresponding to the lactation of 300 primiparous and multiparous Holstein cows were used, collected during1992-2012 in farms located in Casilda, Santa Fe province -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 the values of the milk index (Y) and the total milk production (X), corresponding to each individual were first prepared. Dispersion diagrams were made linking the same indicators, but restricting the association to pure cows and with breeding registers within each production category (low, medium and high). 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 cow breeding record: low production cows: r = 0.739; P <0.0001; cows of intermediate production: r = 0.691; P <0.0001 and high production cows: r = 0.568; P <0.0001. The slopes were positive and significant. A decrease in the value of the slope (P <0.0001) was observed along 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, efficiency in breeding and reproductive efficiency should be incorporated.