Effect of age at first calving on productive parameters in Costa Rican Jersey cows.
The objective of this work was to quantify the effect of age at first calving (AFC) on milk production in the first and second lactation of specialized diary Jersey cows. Records of 28 367 cows belonging to 545 specialized dairy herds, registered in the software VAMPP Bovino 3.0 between January 2000 and December 2010, were used. Descriptive statistics and linear mixed models were performed. The AFC average was 29.35 months (SD: 6.77), with a trend to increase during the study period. A significant effect of the AFC was observed on milk production (kg/305d) in the first two lactations (P<0.0001); in the first lactation, cows with AFC < 25.8 months or between 25.8 and 41.0 months produced -275.81 and -167.70 kg/305d (P<0.0001) than those with AFC >41 months. Cows without retained placenta (RMF) produced +450 kg/305 d (P= 0.0022) than those with RMF. On the other hand, the inbreeding coefficient and type of birth had no effect on milk production. In the second lactation, the independent variables affected the milk production similarly to first lactation; however, the age at second calving did not affect the subsequent production. This study demonstrates the linear effect of AFC on first and second lactation milk production; thus, AFC seems to have an effect not only on first lactation, but also in the productive performance of second lactation.