The investigations were carried out in the period between October 2002 and April 2004 on 404 cows housed on one of dairy farms of the Wielkopolska region and subjected to milk performance testing with the AT4 method. Data for analysis was from the first six test-days. It was found a positive (i.e. disadvantageous) relationship between average milk yield and days open (p≤0.05). A similar relationship was observed between milk fat content on the test-day preceding the first AI service and days open, and the number of AI services per confirmed pregnancy (p≤0.05). Furthermore, a significantly (p≤0.05) lower milk protein content was found on the first test-day after calving in cows in which days open exceeded 150 days, and in cows in which the number of AI services per conception was greater than 3.

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