Effects of parity and milk yield on lactation performance of dairy cows

【Objective】To explore effects of different parity of high-yield and low-yield dairy cows on milk yield,milk composition and lactation persistence,so as to provide reference for raising management pattern optimization and increasing life of dairy cows dairy cows.【Method】12406 dairy cows from 17 dairy farms in Beijing and Hebei Province,China were grouped according to the criterium of high yielding(48.69±6.88 kg/d)and low yielding(23.47±5.28 kg/d).Raw data based on the DHI(Dairy Herd Improvement)report was pretreated to obtain 5158 high-yield dairy cows and3110 low-yield dairy cows. One-way ANOVA was used for homogeneity of variance test and multivariate correlation analysis was conducted by Pearson two-sided test. The differences between groups were analyzed by LDS and Duncan's multiple comparison,and the correlation between the 2 variables was analyzed according to Spearson correlation coefficient.【Result】Parity influenced milk yield,milk composition and lactation persistence:the daily milk yields of the third and fourth parity of high yielding dairy cows were significantly higher than those of other fetuses(P<0.05,the same below)and somatic cell count(SCC)of high-yield dairy cows after the fourth parity was significantly higher than that of other parity;daily milk yield and milk lactose rate of the first parity of low-yield dairy cows were significantly higher than those of other parities,and the SCC was significantly lower than that of other parities. In terms of lactation persistence,the first parity of high-yield dairy cows performed better than the third,fourth and the fifth parity,the first parity of low-yield dairy cows performed better than the other parities and no significant difference was found in other parities(P>0.05,the same below). Lactation persistence of high-and low-yield dairy cows was not significantly correlated with SCC but was significantly correlated with milk yield. Correlations of milk yield,milk component and SCC were consistent except for correlation between dry matter content and milk yield and correlation between milk fat rate and lactose rate. Extremely significant positive correlation was found between daily milk yield and milk lactose rate(P<0.01,the same below)and extremely significant negative correlation was found between daily milk yield and SCC. Composition and persistence between high-yielding and low-yielding dairy cows,and there was a significant positive correlation between daily milk yield and corrected milk and lactose rate. SCC was significantly positively correlated with milk fat rate and milk protein rate.【Conclusion】The third and the fourth parities of high-yield dairy cows performed the best and the first to the third parities of low-yield dairy perform the best. Parity of high-and low-yield cows influences milk yield,milk composition and lactation persistence. But the trend of milk yield and milk composition under different parities is difference. Therefore,with improved basic feeding management,nutrition supply should be optimized,feed formula should be timely adjusted and classification and grouping of dairy cows should be done appropriately to better utilize the optimal parity of dairy cows and increase the economic benefits.