Early lactation extended therapy against Staphylococcus aureus intramammary infections in heifers
Intramammary infections (IMI) in heifers caused by Staphylococcus aureus (S. aureus) are challenging to treat using standard protocols. Recent evidence suggests that an extended treatment protocol with pirlimycin is the most effective way to treat S. aureus IMI in North America. Using on farm culture methods with the PetrifilmTM Staph Express Count (STX) plates can help with the early detection of IMI. The primary objective of this study is to evaluate the cure rate of an extended pirlimycin treatment on heifers in early lactation positive for S. aureus IMI identified using the STX plates. The secondary objective was to assess Petrifilm characteristics when used in a protocol for early lactation detection of infected quarters in heifers. Milk samples were collected from heifers (n=946) in the first few days of calving (mean= 5 days). Heifers with a laboratory-confirmed IMI caused by S. aureus (n=72) were randomly allocated in two groups. The treatment group (n=55 quarters from 39 heifers) received a sterile intramammary infusion of 50 mg of pirlimycin for 8 consecutive days in the infected quarters; the control group (n=43 quarters from 33 heifers) received no treatment. Mammary quarters treated showed a statistically significant cure rate of 64% compared to the control group (33%). Quarters treated were 3.6 times more likely to be cured then the control group. With the STX, a total of 38% of S. aureus positive quarters were identified as other staphylococci with standard culture. The study reveals that a high cure rate for S. aureus IMI can be achieved in dairy heifers if an extended treatment protocol is used soon after calving. Use of Petrifilm for identification of S. aureus infected heifers could lead to many unnecessary treatments because of false positive results.
Staphylococcus aureus Petrifilm Pirlimycin Intramammary infections Heifers Extended therapy