Modelling the impact of changes in productive indicators in dairy cows on the efficiency of feed nitrogen utilization

A generalized analysis of the main approaches to describing and understanding the characteristics of the regulation of the breakdown and fermentation of feed nutrients in cows is presented using the example of the ‘Molly Model’. The research was based on data from 595 Holstein cows kept at the Kolos Agricultural Firm LLC in the Kyiv region. An analysis was conducted of the relationship between such ‘output’ parameters as: milk yield, fat, protein, lactose content, milk urea nitrogen (MUN), live weight of cows, and milk yield adjusted for energy content (ECM). MUN values were used as the main biomarker. Calculations were made of the efficiency of nitrogen use for milk production (MNE, milk nitrogen efficiency) depending on productivity indicators. Based on regression analysis, the following reliable dependencies were obtained: MNE — daily milk yield +3.29; MNE — milk fat content −5.93; MNE — milk protein content −42.32; MNE — lactose content in milk −17.45; MNE — MUN −2.49; MNE — live weight of the cow −0.07; MNE — milk yield adjusted for energy content +3.12. Based on the obtained regression coefficients, possible changes in nitrogen use efficiency were modeled, where an increase in the absolute values of indicators such as fat, protein and lactose content in milk, MUN, live weight of cows and MNE leads to a decrease, and when the daily milk yield and milk yield adjusted for energy content increase, there is an increase in the MNE of the diet for milk production. The data obtained indicate the possibility of using individual or group values of MUN and MNE content in milk production in assessment and selection programs for reliable prediction of the effect obtained for milk productivity, milk composition and production efficiency.