Effect of first lactation milk yield on efficiency of cows in herds with different production levels
Abstract. Lifetime performance was analysed in 6 981 Black and White cows with different proportion of Holstein Friesian inheritance from the active population in the Kujawsko- Pomorskie province according to first lactation yield. It was shown that from the viewpoint of lifetime efficiency, the optimum milk yield of first calvers depends on the milk yield level of the herd. In herds with ≤5 000 kg milk production, the best efficiency was shown by the cows that produced 6 001–7 000 kg milk as first calvers. A decrease in lifetime milk yield, reduced life span and length of productive life, and lower fertility should be taken into account for more efficient first calvers. In herds with 5 000–6 500 and >6 500 kg milk production, lifetime milk yield and milk yield per day of (productive) life increased with increased first lactation milk yield, while fertility deteriorated.