Reproduction efficiencyof Holstein x Gir crossbred animals in Brazilian dairy farms were evaluatedusing data provided by the Brazilian Association of Girolando. A total of 2,600records of age at first calving (IPP) and 3,763 records of calving intervals(IDP) were analyzed using the SAS® GLM procedure. Estimates ofgenetics effects: additive difference between Holstein and Gir breeds, dominanceand additive x additive epistatic effects were obtained by regression modelsincluding genetic groups to model the performance of crossbred groups. The geneticgroup 1/2 showed better performance: lower averages for IPP and IDP than theother groups. It was observed a trend of increasing IDP as the proportion ofHolstein genes increased. The dominance effect influenced significantly bothtraits, while the additive x additive epistatic effects significantly influencedonly IPP. The results indicated that loss of favorable epistatic interactionscontributed to high IPP average in the 5/8 group.
