Genetic parameters of milk production, evaluation of sires, and characterization of dairy farms in the humid tropics of Costa Rica

Abstract

A total of 3 717 records from Holstein (H) and Jersey (J) cows were analyzed to determine the importance of genetic and non-genetic effects on milk production. Genetic population parameters were estimated and the Best Linear Unbiased Predictions (BLUP) technique was used to estimate breeding values of sires. Characterization of the farms by multivariate techniques involved the variables milk production at 305 days (P305), production per hectare, area of pastures and of cut and carry forage, number of lactating cows and concentrates supplied. Four groups of farms were identified. Least squares means of P305 per farm varied from 2 952 ± 150 kg to 6 745 ± 154 kg and those of calving to conception interval varied from 93.4 ± 9.3 to 139.0 ± 8.7 days. The model used to estimate heretability and repeatability of P305 adjusted for lactation length and parity, included the effects of farms, year of calving, season of calving, sire, and cow within sire. Estimates obtained in H were h2 = 0.49 ± 0.17 and r = 0.54 ± 0.03; and in J, h2 = 0.48 ± 0.25 and r = 0.55 ± 0.05. Ninety-three H and 31 J bulls were ranked according to their BLUP values. For H sires these ranged from -1 629 ± 627 to 2365 ± 604 kg and for J sires from -1 379 ± 403 to 1 076 ± 410 kg. The highest ranking sires of both breeds were used only in farms with high intensification levels, while sires with negative values were used randomly. This illustrates the importance of defining the type of sire according to intensification level of the farms. It may be advantageous to use the best sires in farms with the highest production levels, but the use of sires with negative estimated breeding values is never recommended.