Previous and present days open were fit simultaneously as fixed effects in a sire model for 305 day milk production (L305) containing yet the fixed effects of herd-year-season, level of Holstein blood, age of cow as covariant (up to 3rd degree) and the random effects of sire and cow. A relationship matrix including the bull, his sire and his dam was used. The same model without age of cow was used for 305-day mature age equivalent milk yield (PROAJU). The REML method was used to solve the equations by means of the MTDREML program. By the results, the obtained conclusion was that the PROAJU increased 902 kg when the previous days open ranged from 20 to 320 days. This increase was of 813 kg for the same range in the present days open. The sires breeding values for PROAJU were predicted in four data sets using the prior model with exclusion of previous and present days open periods. The production records were adjusted by multiplicative adjustment factors obtained for previous and present days open and the sires were reevaluated. Rank correlation among sire breeding values for adjusted and non-adjusted milk production were nearly 1. The means of the differences among sire breeding values with adjusted and non adjusted milk production for the days open were approximately zero, indicating that factors for days open were appropriate for the data.
genetic evaluation; adjustment factors; days open; milk production; Holstein breed
