Dr. Luciana da Costa, Dept. Veterinary Preventive Medicine, Extension Dairy Veterinarian, The Ohio State University
Staphylococcus aureus is considered the most common contagious pathogen in many dairy farms worldwide, with herd prevalence estimated at 43 and 72% in the USA and Canada, respectively. Management practices, and especially milking procedures, play an important role in control and prevention of these intramammary infections.
Material and Methods
A survey was done among Ohio dairy farms to estimate Staph. aureus prevalence and to evaluate whether certain management practices are associated with finding the organism in bulk tank milk (BTM) of these herds. A mailed questionnaire was sent to 780 Ohio producers to survey them regarding general mastitis control practices in the herds, and their BTM was tested if permission was granted. Up to three BTM samples were collected from each participating dairy farm and cultured for detection of Staph. aureus. A herd was considered positive for the pathogen if at least one of the BTM samples was positive.
The response rate to the survey was 49%. Of the 380 responders, 307 allowed culture of their BTM.
Herd Characteristics - Responding herds were representative of typical Ohio dairy farms, with the majority (89%) having less than 200 cows, milking Holstein cows (80%), and housing them in free-stall barns (75%).
Herd Prevalence of Staph. aureus - if only the first BTM sample per herd was considered, prevalence was estimated to be 48%, but it increased to 69% when all three BTM samples per herd were considered and interpreted in parallel.
Milking Practices - Of the responding producers, 57% reported to check foremilk, 82% used pre-milking teat disinfection (pre-dip), 97% used post-milking teat disinfection (post-dip), 92% used single towels per cow, and 38% segregated known infected cows or milked those cows last. Only 49% of responding herds reported to pre-strip, pre-dip, use single towels per cow, and to post-dip (64% of them Staph. aureus positive). Herds that did not implement all these four practices as part of their milking routine (74% of them Staph. aureus positive) were at 2.0 times higher odds to be found positive for Staph. aureus in BTM than herds that did implement them [P=0.01, 95% confidence interval (CI) for an odds ratio (OR) of 1.1 to 3.2].
Farm Workforce - Owners were responsible for milking cows in 64% of the farms (69% of these herds were positive for Staph. aureus), while the remaining 36% of herds had hired employees assisting with milking (68% positive for Staph. aureus). In 10% of the farms, hired workers were reported to be solely responsible for milking of cows (80% positive for Staph. aureus). These herds had 2.3 times higher odds of having Staph. aureus detected from their BTM than herds where owners were involved in milking (P=0.08, 95% CI for an OR of 0.8 to 6.1).
Detected Staph. aureus prevalence was in agreement with other studies reported from North America. Repeated training and constant motivation may be crucial for implementation of proper milking procedures to maintain good udder health and milk quality in dairy herds.