Milk composition of Holstein cows: a retrospective study

ABSTRACT: Worldwide, milk analysis is an satisfactory measurement of milk quality on dairy farms. Milk composition is the base for payment systems, so knowledge of its characteristics at different periods is essential for modern dairy producer. The aim of the study was to evaluate the effects of year, season, stage of lactation, and lactation number on variations in milk yield and composition of Holstein cows (n=148,604). Milk yield estimated by multiple regression was 25,50L/cow/day. Winter was the season with the highest milk yield and the highest protein and lactose content. Milk fat was highest in the fall, in cows in late lactation and also in primiparous cows. Lactating cows from 6 to 60 days in lactation and those in 2nd or 3rd lactation showed the highest milk yield. Lactose concentration was positively correlated with milk yield. Somatic cell score was negatively correlated with milk yield and with lactose concentration. Most important variations in milk characteristics occur among seasons, lactation stages and parities. Mammary gland health is yet the greatest challenge to be overcome.摘要：在全球范围内，牛乳分析是奶牛场评定牛乳质量的可靠检测手段。牛乳成分是牛乳收购计价体系的核心依据，因此掌握不同时期牛乳的品质特征，对现代奶牛养殖者而言至关重要。本研究旨在评估年份、季节、泌乳阶段以及泌乳胎次对148604头荷斯坦奶牛（Holstein）产奶量与牛乳成分波动的影响。经多元回归分析估算的产奶量为25.50升/头/日。冬季的产奶量以及乳蛋白、乳糖含量均为全年最高。乳脂肪含量在秋季、泌乳后期母牛以及初产母牛群体中最高。泌乳天数6至60天的母牛以及处于第2或第3泌乳胎次的母牛，产奶量最高。乳糖浓度与产奶量呈正相关。体细胞评分（Somatic Cell Score）与产奶量及乳糖浓度均呈负相关。牛乳品质特征的主要波动来源于季节、泌乳阶段以及泌乳胎次的差异。乳腺健康仍是亟待攻克的最大难题。