<span name="style_bold">Additive and non additive genetic effects in Holstein×Jersey and Holstein×Brown Swiss rotational crosses. </span>The objective of this study was to assess the impact of additive and non-additive genetic effects on open days (DO), age at first calving (AFC), herd-life (HL) and daily milk yield (DMY) in Holstein×Jersey (H×J) and Holstein×Brown Swiss (H×BS) rotational crosses. Data were collected in dairy farms from Costa Rica from 1990 to 2009. Effects were assessed by using two models: a statistical model with breed-type as fixed effect and a genetic model based on regression on expected heterocigocity. Correlations higher than 0.90 were obtained between performance predicted by the genetic model and the least squares means obtained by the statistical model. Direct heterosis percentages for H×J vs. H×BS crosses were, respectively: -6.4 vs. -2.2 for DO; -2.5 vs. -2.2 for AFC, 4.4 vs. 12.2 for HL, and 3.2 vs. 3.8 for DMY. According to the genetic model, direct additive effects were significant (P&lt;0.05) for all traits except HL in H×BS; whereas maternal additive effects were significant for HL and DMY in both crosses. Direct heterosis was significant (P&lt;0.05) for DO, AFC and DMY in H×J, as for AFC, HL and DMY in H×BS. Maternal heterosis was significant (P&lt;0.05) for AFC and DMY in H×J; and for DMY in H×BS. Recombination effect was significant (P&lt;0.05) for AFC and DMY in H×J; and for DMY in H×BS. In general, both additive and non-additive genetic effects play an important role in these two crosses.The objective of this study was to assess the impact of additive and non-additive genetic effects on open days (DO), age at first calving (AFC), herd-life (HL) and daily milk yield (DMY) in Holstein×Jersey (H×J) and Holstein×Brown Swiss (H×BS) rotational crosses. Data were collected in dairy farms from Costa Rica from 1990 to 2009. Effects were assessed by using two models: a statistical model with breed-type as fixed effect and a genetic model based on regression on expected heterocigocity. Correlations higher than 0.90 were obtained between performance predicted by the genetic model and the least squares means obtained by the statistical model. Direct heterosis percentages for H×J vs. H×BS crosses were, respectively: -6.4 vs. -2.2 for DO; -2.5 vs. -2.2 for AFC, 4.4 vs. 12.2 for HL, and 3.2 vs. 3.8 for DMY. According to the genetic model, direct additive effects were significant (P<0.05) for all traits except HL in H×BS; whereas maternal additive effects were significant for HL and DMY in both crosses. Direct heterosis was significant (P<0.05) for DO, AFC and DMY in H×J, as for AFC, HL and DMY in H×BS. Maternal heterosis was significant (P<0.05) for AFC and DMY in H×J; and for DMY in H×BS. Recombination effect was significant (P<0.05) for AFC and DMY in H×J; and for DMY in H×BS. In general, both additive and non-additive genetic effects play an important role in these two crosses.

Dairy crosses; heterosis; functional traits; productive traits