Аннотация
Projection factors for 305-day for milk fat and protein yield were calculated for the Italian dairy cattle breeds. Different multiplicative coefficients were calculated for each breed, for first, second, and later parities, and for two different seasons. Cumulative and last sample production are used in extending lactations to 305-day In order to validate the method of prediction, lactations were projected and compared to effective productions. Difference in means and standard deviations between projected and effective 305 productions, and correlation for different classes of lactation length were used as comparison criteria. Where possible data sets used in validation step were different from the data sets used to estimate extension factors. The results indicate an absence of a systematic underestimation or overestimation in predicting 305-day lactations depending from length of partial lactation. A small difference was observed in coefficients calculated for second parity and later parity cows, while coefficients for first lactation records were larger. The method presented will be implemented soon for the routine computation of 305-day lactations in Italy.