Based on the results of milk performance of lactating cows, 15 659 Black-and-White with varied addition of HF genes was evaluated in the course of lactation milk production depending on the length of the dry period before the full lactations investigated. Breast plotted curves according to selected groups of animals Wood’s model. The average milk yield of ECM, the study population was: 6 573 kg of standard lactation and 7 063 kg in the lactation lasted an average of a full 352 days. It also showed that these cows, calving over the years 1995–2008 were marked by very high persistence of lactation. The average monthly decline in milk production after peak lactation was 3.52% (LPI = 31.7%). Of the four genetic groups rated highest in the persistence of lactation (the lowest rate of LPI) had a cow with the shortest period of the dry, less than 45 days in three groups of genes, Black-and-White animals which, in its genotype from 50.1 to 75% HF, from 75.1 HF to 99.9% and cows Polish Holstein-Friesian (100%). Monthly average daily milk yield decrease in ECM from 1 month of lactation, for these groups of animals ranged from 1.9% to 3.4%.

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