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 (GI
) and maternal (GM) additive effects, individual (HI
) and maternal (HM)
heterosis and individual recombination effect (RI
). 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 GI and GM 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 HI 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.