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Background. The quality of dairy products, raw milk in particular, depends on many factors. Low bacterial and somatic celi counts are basic determinants of the appropriate raw milk quality. The objective of the work was to assess the effect of selected factors, that is, the age of cows and their daily milk performance, on cytological quality (somatic celi count) and energy value of milk produced at individual stages of lactation. Material and methods. Somatic celi count and energy value of cow’s milk were assessed. A total of229 792 milk samples were examined. Data for analysis were taken from milk records of 350 dairy herds Results. It was demonstrated that, of all the lactations studied, the first lactation (from calving to the l00th day of lactation) was characterised by the highest daily milk performance (25.1 kg) and the lowest somatic celi count (356 thous./l ml), fat, protein and dry matter contents (4.06, 2.96 and 12.41%, respectively) and milk calorific value (732 kcal/kg). The highest energy value was recorded in cow’s milk produced towards the end of lactation, that is from day 300 till the end of lactation (842 kcal/kg). Conclusions. High milk calorific value in late lactation and high fat and protein contents were accompanied by low raw milk quality.
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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