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The efficiency of protein metabolism in cows, the level of consumption and the quality of ‘input’ protein in the diet is reflected in an indicator such as milk urea nitrogen (MUN), which is an important biomarker of these processes. MUN variability is closely related to the quality and structure of the total mixed ration (TMR), physiological and genetic factors.

The study evaluated the variability and relationship between milk yield and the main components of milk (fat, protein, lactose, MUN content), as well as the level of MNE (nitrogen efficiency).

It was found that seasonal fluctuations (year – month of calving) had the greatest impact on MNE indicators, accounting for 9.3% (P>0.999). No significant influence of genetic factors (bull influence) on this indicator was found.

The values of phenotypic correlation coefficients between daily milk yield and the main components of milk (fat, protein, lactose content), as well as MUN and MNE levels for milk production, made it possible to identify reliable dependencies. Thus, the value of MNE for milk production negatively correlates with the fat content in milk (Р>0,999), protein in milk (Р>0,999), lactose in milk (Р>0,999), and urea nitrogen content in milk (Р>0,999).

A positive correlation (Р>0,999) was also found between milk yield and MNE for milk production, and a negative highly significant correlation between MNE and MUN content (Р>0,999). A reliable directly proportional regression dependence of changes in daily milk yield on MNE indicators for milk production was calculated.

Analysis of the absolute values of fat, protein and lactose content proves the existence of a negative regression dependence with MNE on milk production. The results obtained indicate the need to include MUN values to optimize feeding programs and animal welfare management, and knowledge of the relationship between milk components and MNE for milk production indicates the need to model possible changes in each of these components.

 

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