2OHZ Dębołęka Sp. z o.o.,

The aim of the study was to analyse the effect of non-genetic factors on fertility indices in high-yielding Black-and-White Polish Holstein-Friesian cows. The analysis covered 2414 re-productive periods in 1063 cows born in the years 1999-2008. Fertility indices of the cows were evaluated. The age of heifers at first calving was found to decrease in successive years in the population analysed. A shorter rearing period for heifers was not found to negatively affect fertility indices during their later productive life. A significant decrease in reproductive efficiency was observed in the case of yield exceeding 3600 kg over 100 days of lactation in primiparous cows. However, milk yield in the previous standard lactation had the strongest influence on fertility indices. Where milk yield exceeded 9000 kg, each increase of 2000 kg had a significant (P≤0.01) negative effect on all the fertility indices evaluated in the study. KEY WORDS: cows / high yield / fertility indices In 2011 an increase was once again noted in the milk yield of cows undergoing produc-tion value assessment in Poland. Compared with 2010, milk yield increased by 155 kg (from 6980 to 7135 kg), while the number of cows included in the active population increased by 2 % [18]. The growing production potential of dairy cows can negatively affect reproductiv