Influence of lactation period and ketosis on blood ammonia in cows

Abstract

Ammonia is a central component in ruminant nitrogen metabolism and serves as a sensitive indicator of the dynamic balance between nitrogen intake, rumen microbial activity, and hepatic detoxification efficiency. Once produced in the rumen, ammonia is absorbed into the bloodstream and must be rapidly cleared by the liver via the urea cycle. As such, blood ammonia concentration reflects both the rate of ammonia production and the liver’s detoxification capacity, making it a valuable marker for evaluating protein metabolism and liver function. This study aimed to assess how different lactation stages and the presence of ketosis/hepatic lipidosis affect blood ammonia levels in dairy cows. A total of 50 Holstein-Friesian cows were examined, with 10 animals assigned to each experimental group. Ammonia levels (μmol/L) in blood plasma varied significantly depending on lactation stage and metabolic condition. In early lactation, the mean concentration was 67.64±6.52, which significantly decreased at peak lactation (34.11±7.5), followed by mid-lactation (29.93±7.9), and reached its lowest in the dry period (21.61±6.1). Cows diagnosed with ketosis exhibited significantly higher ammonia levels (96.52 ± 8.2). A significant positive correlation was found between ammonia and BHB (r = 0.54) as well as with the index of hepatocyte steatosis index (nonesterified fatty acid: cholesterol, NEFA:CHOL ratio) (r = 0.81), and significant negative correlations with the liver functionality index (r = –0.82), urea (r = –0.47), total protein (r = –0.38), and albumin (r = –0.36). These findings support the use of ammonia concentration as a reliable biomarker for metabolic and liver function assessment in dairy cows.