Evaluation of the energy-protein balance of feed rations for Montbeliarde cows on the basis of protein and urea content in their milk

The aim of the study was to evaluate the energy-protein balance of feed rations for Montbeliarde cows on the basis of protein and urea content in their milk. In 2016 the herd numbered 319 cows, with mean yield 9,374 kg of milk. The cows were housed in a free-stall barn on deep litter and fed Total Mixed Rations (TMR), the composition of which was balanced according to Deutsche Landwirtschafts Gesellschaft (DLG) norms. The data used in the study were obtained from milk performance evaluations. It was found that only 22.9% of milk samples indicated that the cows were appropriately supplied with protein and energy. Excess protein (>3.6%) was observed in 41.4% of cases of optimum urea content, which suggests an energy surplus in the feed rations. In 3.9% of samples optimal urea content was accompanied by an insufficient protein level (<3.2%), which may be indicative of an energy deficit. An excessive urea level was noted in as many as 22.9% of samples, including 9.3% with a protein level indicating an excessive supply of energy and 2.6% with a protein level indicating an energy deficit. Samples indicating a correct energy-protein balance in the feed rations were noted least often in feeding group 5 (4.5%) and in the cows with the lowest daily yield (4.3%). In each feeding group the protein level in the milk indicated an excessive supply of energy more often than a deficiency, and in groups 4 and 5 the percentage of samples in which the protein level exceeded 3.6% was very high (84.7% and 92.4%, respectively). In the case of lower daily yield (=15 and 15.1-25 kg), a protein deficiency in the feed rations was noted more often (30.1% and 17.7% of samples) than an excessive level (4.3% and 11.6%). In the case of higher yield (>25 kg) the tendencies were reversed, i.e. a higher percentage of samples were indicative of excessive protein (21.5-34.1%) and fewer suggested a deficit (1.6-6.7%). In the case of optimal protein and urea levels in the milk (group 5), the daily yield of the cows was 37 kg of milk. It contained 3.7% fat, 3.43% protein, 4.87% lactose and 12.6% dry matter. The cows producing milk with protein and energy levels indicating a deficiency of energy and an excess of protein in the feed rations were much more productive (group 3). Daily yield of cows whose milk had an insufficient level of urea (groups 1, 4 and 7) was much lower than in the case of the cows whose milk had too much urea (groups 3, 6 and 9). The lowest daily yield (19.5 kg), accompanied by the highest content of protein (4.02%) and dry matter (13.5%) and one of the highest levels of fat (4.16%), was noted in the group in which the protein and urea levels in the milk suggested a protein deficiency and an excess of energy in the feed. It can be concluded from the analysis that the results of milk performance evaluations regarding protein and urea levels in the milk should be given greater consideration in composing TMR feeds for various feeding groups.