华南地区荷斯坦牛泌乳性能在季节、胎次、泌乳时期影响下的变化规律

【目的】分析华南地区季节变化、繁育胎次、泌乳时期对泌乳性状的影响。【方法】采集广州某规模化牛场2015年全年10 450头次的荷斯坦牛的奶牛群改良计划(DHI)测定数据,提取产奶量、乳脂率、蛋白率和脂蛋比等泌乳性状数据,运用统计模型评估季节、胎次、泌乳时期等因素对泌乳性状的影响,分析各性状之间的相关性。【结果】季节、泌乳时期和胎次分别对产奶量和乳成分含量产生极显著的影响(P0.001)。夏季产奶量极显著低于其他季节(P0.01);在乳成分上,夏季的各项指标均为最低值,且极显著低于春冬季节(P0.01),春季各项指标值极显著高于冬季(P0.01);产奶量和乳蛋白率在12月(非气温最低的1月)达到最高值;不同胎次牛的产奶量上,1胎牛在第3个泌乳月份达到泌乳高峰,其他胎次牛则出现在第2个泌乳月且峰值高于1胎牛,但1胎牛产奶量下降速率明显低于其他胎次牛。1胎至2胎牛产奶总量逐渐升高,之后随着胎次的增加而下降;从乳成分的变化来看,各项指标在第1胎次时最高,随着胎次的增加逐步降低,到4和5胎时出现增加。在泌乳时期内,脂蛋比出现前期高后期低的变化规律,且乳脂率和乳蛋白率之间存在极显著的正相关性(r=0.63,P0.01)。【结论】华南地区泌乳牛不仅遭受长期的热应激影响,在冬季同样受到低温冷应激作用而制约其泌乳性能。高胎次(3胎以上)奶牛所占的群体比例较低导致全年泌乳胎次较低,同时当前的日粮营养和饲养水平已严重阻碍高胎次牛在泌乳后期的生产表现。

Variation in milk performance of Holstein dairy cows under the effects of season, parity and lactation stage in South China

Objective To identify the effects of season change, parity and lactation stage on milk performance traits of Holstein dairy cows in South China. Method Dairy herd improvement (DHI) records of 10 450 Holstein cows were collected from a large dairy farm in Guangzhou throughout 2015. Information of milk performance traits including milk yield, milk fat percentage, milk protein percentage and fat-to-protein rate were extracted. The effects of season, parity and lactation stage on milk performance traits were evaluated. The correlations among factors and traits were analyzed. Result Season, parity and lactation stage all had highly significant effects on both milk yield and milk nutrient contents (P<0.001). Summer milk yield was highly significant lower compared with the other seasons (P<0.01). All indexes of milk constituents reached the lowest in summer and were highly significantly lower than those in spring or winter (P<0.01), and the spring values were significantly higher than winter values(P<0.01). Milk yield and milk protein percentage were the highest in December, but not in January which was the coldest month of the year. Peak milk yields of first-parity cows reached during the third month of lactation, but those of the other parity cows reached during the second month of lactation with higher peak values compared to first-parity cows. However, the decreasing rate of milk yield was slower in first-parity cows than in the other parity cows. Milk yield increased gradually from first to second parity, and then decreased with rising parity. For milk constituents, all indexes reached the maximum at first-parity, decreased gradually with rising parity and then increased from fourth to fifth parity. During lactation, fat-to-protein rate was higher at an early stage and lower at a later stage, and there was highly significant positive correlation between milk fat and protein percentages(r=0.63, P<0.01). Conclusion Lactation cows of South China are subjected not only to heat stress in summer, but also to cold stress in winter, which restricts the milk performance traits. High parity (above third-parity) cows account for a low percentage of the studied population, resulting in a low value of annual milk parity. Low dietary nutrition and feeding level are strongly restricting the production performance at a later lactation stage for high parity cows.