Effect of extended lactations on cow milk and reproductive performance

Abstract. Frequency of extended lactations and their effect on milk and reproductive performance of cows from the active population of 11 891 Black and White cows with different proportions of Holstein Fresian inheritance were analysed. It was found that lactations longer than a 305-day standard lactation were quite common in the analysed population of Black-and-White cows improved with the Holstein-Friesian breed. The age of cows, the level of yield in a standard lactation and season of the year had a significant effect on the proportion of extended lactations. Lactation extension had a beneficial effect on milk yield in full lactation but was detrimental to fertility. The efficiency of lactation extension was found to increase with the increasing level of yield in the standard lactation.