Milk fat-to-protein ratio as a marker of blood metabolic changes related to subclinical ketosis and low-grade ruminal acidosis in early lactation dairy cows

Objectives: This studyʼs primary objective was to investigate the connection between the milk fat-toprotein ratio (FPR) and the metabolic changes associated with subclinical ketosis and low-grade ruminal acidosis in Holstein dairy cows during early lactation. The researchers aimed to validate FPR as a non-invasive indicator for these metabolic disorders by correlating it with specific blood biochemical markers. Methods: Twenty-seven cows, ranging from 9 to 59 days postpartum, were sorted into three distinct groups based on their FPR values: • Low-grade ruminal acidosis (FPR < 1.2) • Metabolically healthy (FPR 1.2–1.5) • Subclinical ketosis (FPR > 1.5) Milk composition was continuously monitored using a Brolis HerdLine in-line analyzer. To assess metabolic health, weekly blood samples were collected and tested for various parameters, including iron, glucose, and non-esterified fatty acids (NEFA). Results: The analysis revealed significant differences among the groups: • Cows with subclinical ketosis showed significantly higher NEFA levels compared to the ruminal acidosis group (p < 0.01), a finding consistent with the enhanced fat mobilization that occurs during a negative energy balance. • Serum iron levels were significantly lower in the ketosis group than in the ruminal acidosis group (p < 0.01). Furthermore, the ruminal acidosis group also had significantly lower serum iron than the metabolically healthy cows (p < 0.01), highlighting that iron metabolism is disrupted in both conditions. • Correlation analysis supported these findings: FPR positively correlated with NEFA (r = 0.281, p < 0.01) and negatively correlated with serum iron (r = –0.308, p < 0.01). Conclusions: The study concluded that FPR is a reliable indicator of metabolic health in early-lactation dairy cows. It accurately reflects key metabolic alterations, such as elevated NEFA in ketosis and reduced serum iron in both ketosis and ruminal acidosis. These results confirm the utility of FPR as a simple and practical tool for the early detection and management of subclinical metabolic disorders in dairy cows.