Abstract
This study evaluated the overall and lesion-specific effects of clinical lameness on milk yield and milk composition traits in Holstein dairy cows under commercial dairy farm conditions. A total of 18,254 test-day records from 2049 clinically lame cows in two large commercial dairy herds located in Varamin County, Tehran Province, Iran, were included in the analysis. Milk yield, milk fat percentage, milk protein percentage, and somatic cell count (SCC) were compared between pre-lameness (within 30 days before diagnosis) and post-lameness (within 30 days after diagnosis) periods using linear mixed-effects models. Herd, parity, and days in milk (DIM) were included as fixed effects, and cow was fitted as a random effect. SCC values were log10-transformed prior to analysis. Overall, lameness significantly reduced daily milk yield (by approximately 1.3 kg/d; P P P = 0.15). Lesion-specific analyses showed that digital dermatitis, sole ulcer, phlegmon, white line disease, and foreign-object injury were associated with significant yield reductions (P < 0.01), whereas hoof crack had no significant effect. Changes in milk composition varied across lesion types and were generally smaller in magnitude than yield reductions. These findings highlight the production and welfare implications of lameness and emphasize the importance of early detection and lesion-specific management strategies.