Presence of pathogens DNA is associated with altered milk yield and composition in cows close to dry-off

The aim of this study was to investigate the effect of presence of pathogens DNA (i.e. S. aureus and S. agalactiae) on milk yield and composition in apparently clinical healthy cows close to the dry-off (days in milk >270). Non-aseptically collected composite milk samples collected on the day of the official milk testing were analysed using quantitative PCR for DNA detection. Milk yield was available for each cow and quality traits were predicted on the same samples through the CombiFossTM 7 analyser (Foss Electric A/S, Hillerød, Denmark). After editing, 1,529 Holstein Friesian cows reared in 98 herds located in the northern Italy were available to estimate the least square means of the traits investigated through a linear mixed model which included pathogen class (presence vs absence), parity and classes (n=4) of days in milk as fixed effects. The random effects were the herd‐test‐date and the residual. S. aureus and S. agalactiae DNA were detected in 14.8% of the samples. Cows with DNA pathogen presented lower milk yield, lactose content and casein index compared to cows free of pathogens. The same were characterized by greater total and differential somatic cell count. The monitoring of udder health, especially in cows close to dry off, is useful for the smarter use of antimicrobial.