Estimation of heterotic components for lactation traits and reproductive performance in three crossbreeding trials of Holstein cattle with German Friesian raised under hot climatic conditions

Lactation traits and reproductive performance of three trials of crossing Holstein cattle (H) and German Friesians (F) raised in a hot climatic were evaluated. The first 90-day (M90), 305-day (M305) and total milk yield (TMY), 305-day milk yield per day of calving interval (MCI1), total milk yield per day of calving interval. (MCI2) along with length of lactation period (LP), age at first calving (AC1) and calving interval (CI) were used. For these traits, a genetic model was applied for each trial separately to obtain estimates of individual (G(I)) and maternal(G(M)) additive effects, individual (H-I) and maternal (H-M) heterosis and individual recombination effect (R-I). Data of 8045 normal lactations from the three trials were analysed. Among the crossbreds obtained in the three trials, cows of 3/4H1/4F ranked first in their lactational performance. Estimates of G(I) and G(M) were generally large and in favour of H cows (daughters) and dams for most milk-yield traits, CI and AC1 in the three trials. Estimates of H-I in crossbred cows for milk traits, CI and AC1 were mostly negative and reveal that crossing F with H was associated with a reduction in milk-yield traits, shorter CI and earlier AC1 along with longer LP in the three trials. Estimates of HM for milk yields, LP, AC1 and CI in daughters of crossbred dams were mostly negative. Recombination losses in crossbred cows were negative for milk yield traits, AC1 and CI in most cases.