Assessment of dairy cow energy status using milk fat, protein and urea concentrations

One of the ways to make an assessment of the energy status of cows in lactation is to consider the results obtained from the evaluation of the concentrations of organic milk components. The advantages of this method are that the taking of milk samples is not stressful for the cow and that it is also possible to use the results of milk examinations carried out by dairy plants within regular control. A bulk milk sample from all individual cows can be used, or an individual milk sample. In farms that have herds of unequal genetic potential, it is preferable to assess the energy status by analyzing the results for individual samples, because each animals is assessed individually in that way. Furthermore, the use of individual milk samples is recommended at newly-established farms in order to facilitate the establishment of reference values for the herd. The energy status of cows is assessed using the milk samples by analyzing fat, protein and urea concentrations and their mutual ratios. Fat and protein concentrations in cow milk vary depending on the breed, the diet, age, stage of lactation, and the season of the year. A fat content lower than the physiological values can be expected in cases of unfavourable diet of the cows during the period around calving or rumen acidosis, and it can be expected to be higher during ketotic conditions. A higher protein content in milk can be expected during a high-protein, and a lower one during a low-protein diet of the cows. The physiological concentration of urea in milk depends on nutritive factors, the season, age, stage of lactation, and body mass. Specifically, older cows, cows in advanced lactation, and cows in the summer period tend to have higher values for urea concentration in milk. Among nutritive factors, the most important is the ratio between energy and proteins in the cow feed ration. In cases when protein content in milk is optimal or above the recommended values but the energy supply is lower, the urea concentration increases to over the range of physiological values. In the event that the feed ration is deficient in both proteins and energy the urea content in milk drops. This work also presents a model for assessing the energy status in cows by analyzing the mutual ratios between the individual milk components (proteins and fat, or urea and proteins) in the individual milk samples. It is possible to determine the energy status of the animal on the basis of the ratio between proteins and fat, and the supply of the cow with proteins and energy on the basis of the ratio between urea and proteins.