Analysis was made of the effect of dry period length in first-calf heifers and older cows from the active population of cows in the Pomerania and Kujavia regions on their performance in the next production cycle. The GLM, FREQ and CORR PEARSON procedures of the SAS package were used for statistical calculations. It was found that a dry period of 41-60 days is the most favourable in terms of next lactation milk yield. Any shortening of the dry period, especially to less than 20 days, is particularly inadvisable for first-calf heifers. Dry periods of 21-40 days are the most favourable considering survival of cows (especially the oldest cows) in the next production cycle. Extending the standard dry period of 41-60 days by 20 days causes a slight decrease in performance (as determined by the parameters mentioned above) but extending it by another 20 days is highly detrimental. Especially in the oldest cows, a dry period that is too long (over 100 days) may carry the risk of increased culling in the herd, shorter lactations and poorer reproductive performance.
