One analysed the effect off some factors on twenty-four hours yield, chemical composition and somatic cells level in milk from 163 196 control milking of cow active population on Pomerania and Kujawy, Poland. Heritability of milk traits was estimated by REML method. One showed that basic components content is only to a little higher degree conditioned hereditary than their productivity and was from 0.19 to 0.25, whereas h² of somatic cells number was 0.14. One found the significant increase in productivity and upward tendency to fat and albumen content as well as to somatic cells number, together with an increase of Holstein Fresian (hf) race gene share. One showed that twenty-four hours yield of cows was higher almost by 11% in spring comparison to autumn. With summer milk contained less fat and albumen, besides sanitary quality of milk definite as somatic cells number was the worst. One observed upward tendency to twenty-four hours milk yield and worsening of milk quality with an increase of heads number.

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