The objective of this work was to evaluate the effects of previous and present days open and previous dry days period fitted simultaneously as fixed effects using a sire model for 305-day milk production, still containing the fixed effects of herd-year-season, genetic group, age of cow and the random effects of sire and cow. An additive relationship matrix that included the bull, its sire and its mother was used. The same model with the exclusion of the age of cow was used to the milk production adjusted to a 305-day mature equivalent basis The analysis solutions were obtained using derivative free restricted maximum likelihood. Solutions were smoothened with orthogonal polynomials. Predicted values for 305-day milk production were not presented because they followed the same trend as did milk production adjusted to a 305-day mature equivalent basis. As previous and present days open increased from 20 to 300 days, the milk production increased 950 and 802 kg, respectively. Cows with days dry between 60 to 80 days obtained higher milk production in the following lactation. Heritability estimates were .02 for days open and .08 for days dry, when total milk production was considered in the model, and .12 when it was excluded. Multiplicative adjustment factors were developed to adjust production for the effects of days open and days dry.
adjustment factors; days open; days dry; milk production; Holstein breed