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

Milk urea content is influenced by a large variety of factors, including the quantity and quality of protein fed and its balance with energy, diurnal fluctuations, management, season, and analysis method, as well as individual cow factors, which include the health status of the cow. The aim of this study was to investigate the effects of metabolic disorders (ketosis and ruminal acidosis [indicated by the fat and protein content of the milk]), as well as high SCC and udder diseases, on the milk urea content of dairy cows from different regions and farms across Germany. For this purpose, we analyzed 5 independent datasets containing information derived from monthly milk recordings (dataset A, 6,140,342 test day records in 2015; dataset D, 439,767 test day records in 2020-2023; dataset E, 399,279 test day records in 2019-2020) in combination with the differential SCC in datasets D and E, or individual recordings of daily feed and energy intake and milk analysis (dataset B, 58,235 test day records in 2014-2017; dataset C, 352,346 test day records in 2018-2021). 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-oriented energy supply. The results for the effect of a very high energy supply were inconsistent across the 5 datasets. Furthermore, the milk urea content of cows with the highest SCC were observed to be 9.0 to 13.0 mg/L lower in comparison to cows with a healthy udder. Moreover, the milk urea content was 14 mg/L lower in cows diagnosed with mastitis compared with those without a diagnosis. Although this may have an impact on judgments 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 herds with a high prevalence of sick cows.