Study On Correlation Between Milk Performance And Nutritional Assessment Parameters During Different Lactation Stages Of Dairy Cows

The study selected the lactation Holstein cows in different lactation stages as experimental animals. The experiment was conducted to analyze serum biochemical parameters of dairy cows and their correlation with milk production performance, and to provide scientific basis for establishment of inspection system of cow nutritional status and for scientific evaluation of the nutritional status and reasonable ration formulation with dairy cows.The paper consists of two parts.Experiment1was carried out in ranch A of Inner Mongolia. Two factors completely randomized experimental design was adoped. One hundred and eighty Holstein cows were divided into nine groups with20replicates in each group in order to research the effect of lactation stages and milk production on the contents of VA, VE and Se in serum, analysis the relationship between VA, VE and Se content in serum and milk performance. One of the factors was stage of lactation (early lactation, mid-lactation and late lactation). The second factor was milk production, including high-yielding, middle-yielding and low-yielding.Experiment2was carried out in ranch B of Inner Mongolia. The experimental design was same as experiment1in order to research and analysis the changes of NEFA, BUN, Ca, P, AKP contents in serum of dairy cows at different stages of lactation and milk production, and to analysis the relationship between them and milk performance.The main conclusions were included as follows:(1) Milk composition was significantly affected by the stage of lactation and milk production, non-fat milk solids, milk fat and protein content in late lactation was significantly higher than the early and mid-lactation; and the contents of milk protein and non-fat milk solids for high-yielding cows were significantly higher than middle-yielding and low-yielding cows; low-yielding cows’milk fat content was significantly higher than high-yielding cows.(2) From early to late lactation, the contents of VA and VE in serum were gradually increased, and those in late lactation were higher than early and mid lactation. VA content in serum of high-yielding and middle-yielding cows was significantly higher than that of low-yielding cows, and VE contents in serum of middle-yielding and low-yielding cows were significantly higher than those of the high-yielding cows, but serum Se content was dramatically lower than that of high-yielding cows.(3) From early to late lactation, the concentrations of NEFA, Ca and P in serum of dairy cows were gradually decreased, but the AKP activity and BUN content in serum were gradually increased.(4) The correlation between biochemical parameters in serum and milk performance of dairy cows was related to the stage of lactation and milk yield, especially in early lactation. In early lactation, the contents of the VA, Se, NEFA and BUN in serum were significantly positively correlated with milk production, but the content of Ca in serum showed a significant and strong negative correlation. In late lactation, there was a significant negative correlation between milk production and VE content in serum.(5) In early lactation, the contents of VA, Se, NEFA, BUN and Ca in serum could be used as key parameters to evaluate the nutritional status of lactating cows.