Milk production of crossbred Holstein × Zebu cows in the northeastern region of Paraná State

The objective of this work was to evaluate milk production of a Holstein × Zebu herd managed on a semiintensive system at Estação Experimental Joaquim Távora, IAPAR, in the northeastern region of Paraná - Brazil. Two hundred and seventeen records on milk production per lactation period (MY), milk production up to 305 days of lactation (MY305) and length of lactation period (LL) of 82 crossbred cows varying in breed composition were analyzed according to a linear statistical model that included the fixed effects of breed composition, season and year at onset of lactation, order of parturition and place of birth, in addition to the experimental error. Cows born in Joaquim Távora had longer lactation periods and produced more milk than cows born in Ibiporã. The effects of year and season at the beginning of the lactation period influenced all three traits. Both milk production per lactation period and milk production up to 305 days of lactation that began from April to June were superior to those that began from October to December, as well as to those starting from January to March. The order of parturition had a strong effect upon both milk production per lactation period and milk production up to 305 days of lactation. Maximum milk production was attained during the sixth lactation period, although no difference was detected for the contrasts between the sixth and other higher order lactation periods. All traits increased as the proportion of Holstein in the breed composition of the animal increased from 0.5 to 0.875 and decreased thereafter. These results support the argument against complete grading up to Holstein in semi-intensive production systems in sub-tropical regions