Lameness-associated changes in milk yield, composition, and inflammatory quality indicators in dairy cows under tropical conditions in Bangladesh.

Lameness is a major welfare and economic challenge in dairy herds and is associated with reduced milk yield and compromised milk quality; however, evidence under tropical production systems such as Bangladesh remains limited. This observational study was conducted at a commercial dairy farm in Mymensingh, Bangladesh (July 2024-June 2025) to evaluate the effects of lameness on milk yield and inflammatory milk quality indicators. Sixteen Holstein-Friesian lactating cows were enrolled, including 12 clinically lame cows and 4 healthy controls. Lame cows were observed at three predefined stages: 7 days before clinical diagnosis, on the diagnostic day, and 7 days after diagnosis; healthy cows were sampled once as baseline references. Lameness was assessed using a standardized 1-5 locomotion scoring system. Milk yield was obtained from farm records, and milk quality traits, including pH, electrical conductivity, somatic cell count (SCC), fat, protein, lactose, solid-not-fat, and total solids, were analyzed using Ekomilk Horizon Unlimited. Multivariable linear mixed-effects models revealed a significant reduction in milk yield during lameness (15.0 +/- 0.6 L/day) compared with pre-diagnosis values (19.0 +/- 0.5 L/day; p < 0.001), representing a 21% decline. SCC increased more than two-fold (812.8 +/- 45.6 × 10^3 cells/mL; p < 0.001), accompanied by significant increases in electrical conductivity, pH, milk fat, lactose, and total solids. Diagnostic-day lameness showed strong positive correlations with SCC (r = 0.84) and electrical conductivity (r = 0.89), and a strong negative correlation with milk yield (r = -0.76). These findings indicate that lameness is associated with measurable changes in milk quality and reduced milk production under tropical Bangladeshi field conditions.