LENGTH OF LIFE AND MILK PRODUCTION EFFICIENCY IN COWS WITH VARYING LACTATION PERSISTENCY

A total of 2,484 lactations in 760 Polish Holstein-Friesian cows were analysed. Calculations were made of length of life, length of productive life, total number of days in milk, number of calvings, ratio of days in milk to length of productive life, lifetime milk yield (kg), daily yield at the peak of lactation (kg) and lactation persistency as the percentage difference between daily milk production in the 2nd and 10th month in milk. The cows were divided into three groups according to lactation persistency (decrease in production): group I - up to 30%, group II - 30.1-50% and group III - over 50%. Lactation persistency significantly influenced (P <= 0.01) length of life and efficiency of milk production in the analysed cow population. Cows with yield over 30 kg at the peak of lactation followed by a moderate decrease (40%) lived longest (over 6 years) and produced the most milk (nearly 28,000 kg). Yield of primiparous cows at the peak of lactation and its course were found to have a significant effect on length of life and lifetime milk production. The long period of high peak yield (over 30 kg of milk) in the primiparous cows in group I (with the best lactation persistency) in the long term proved to be detrimental, as these cows had the shortest productive life (2.3 lactations on average) and lifetime milk yield about 4,000 kg lower than in the cows in groups II and II (with the poorer lactation persistency).