Incorporation of lactations with non-conventional drying-off causes in genetic evaluation of Gyr dairy cattle

Abstract

-Test-day records of milk yields from the first three lactations were used to verify consequences of incorporation of lactation with non-conventional drying-off causes in genetic evaluation of Gyr dairy cattle. The first file (File1) was composed of test-day records of lactations with conventional drying-off causes. In the second file (File2), the test-day records of lactations with non-conventional drying-off causes were included, such as drying-off by death or separation of the calf, disease, death or sale of cow, and removal of cow from milking control. Data were analyzed by mixed models, using an autoregressive process to adjust the random effects of long-term and short-term environment. The inclusion of test-day records from lactations with non-conventional drying-off causes increased the number of controls by 12% and the number of cows by 18%, and it generated an increase in the estimates of variance components. These results impacted estimates of heritability, calculated at 0.32, 0.28 and 0.26 for the first, second and third lactations in File1, respectively, while in File2 they were 0.34, 0.30 and 0.28 to the same lactation order. The estimated accuracy of predicted breeding values in File2 were higher in relation to File1, but the Pearson and Spearman correlations between predicted breeding values of animals in the two files were high. Lactations with non-conventional drying-off causes can be incorporated to the routines of genetic evaluation of Gyr dairy cattle, because they provide higher estimates of heritability and accuracy of breeding values, which could raise expectations of genetic gains with selection.

Genetic parameters and genetic trends for production traits in dairy Gir cattle

“…This widespread distribution is mainly due to the fact that these animals can be raised on pasture, in addition to their resistance to endo-and ectoparasites and to high temperature. Part of the evolution and expansion of this breed is due to the contribution of the National Dairy Gir Breeding Program (PNMGL) through the identification of superior sires by progeny tests; this program is conducted by the Brazilian Association of Dairy Gir Breeders (ABCGIL) and by the Empresa Brasileira de Pesquisa Agropecuária (EMBRAPA) since 1985 (REIS FILHO et al, 2012), with support from other institutions. Monitoring of results and evaluations of progresses are required in any breeding program, as well as adjustments to optimize genetic gains and increase profits over time (CANAZA-CAYO et al, 2016).…”