Influences of fat-protein-ratio and udder health parameters on the milk urea content of dairy cows.

The milk urea content is influenced by a large variety of factors, including the quantity and quality of protein fed, its balance with energy, diurnal fluctuations, management, season, analysis method, and also individual cow factors which include the health status of the cow. Aim of this study was to investigate the effects of metabolic disorders (ketosis, ruminal acidosis; indicated by the fat-protein-content of the milk) as well as high somatic cell counts and udder diseases on the milk urea content of dairy cows from different regions and farms across Germany. For this purpose, 5 independent data sets which contain information derived from monthly milk recordings (data sets A (6,140,342 test-data in 2015), data set D (439,767 test-data in 2020-2023), data set E (399,279 test-data in 2019-2020)) in combination with the differential somatic cell count (DSCC) in data set D and E, or individual recordings of daily feed and energy intake and milk analysis (data set B (58,235 test-data in 2014-2017) and data set C (352,346 test-data in 2018-2021)), were analyzed. The group of cows with severe energy deficiency showed a 11.0 to 20 mg/l higher milk urea content than cows with a demand-orientated energy supply. The results for the effect of a very high energy supply are inconsistent across the 5 data sets. Furthermore, the milk urea content of cows with the highest somatic cell count are observed to be 9.0 to 13.0 mg/l lower in comparison to cows with a healthy udder. Moreover, the milk urea content is 14 mg/l lower in cows diagnosed with mastitis compared with those without a diagnosis. While this may have impact on judgements for the individual cow, in groups of cows, individual incidences of a disease will not have a significant impact on the average milk urea content. However, this should be taken into account for herds with a high prevalence of sick cows.