In the dairy sector, it has been common practice to systemically dry off cows with long-acting antimicrobials, the so-called blanket dry cow therapy (BDCT), in order to prevent new infections from occurring during the dry period and to cure existing infections. Yet, because of the merely preventive nature of dry cow antimicrobials and the large potential reduction in antimicrobial use when leaving this practice, an increased focus has been placed on selective dry cow therapy (SDCT). This is a targeted antimicrobial treatment of only those cows with evidence of an udder infection present at drying off.
Test-day somatic cell counts (SCC) before drying off and after calving were used to determine the cow’s udder health across the dry period and to study the impact on the performance in the next lactation. Despite the fact that BDCT was applied in all herds participating in this field study, still 12.6% of the cows acquired a new intramammary infection (IMI) across the dry period, when using a SCC threshold of 200,000 cells/mL to define cows to be infected or not. Moreover, these newly infected cows were at a higher risk for elevated test-day SCC throughout the whole subsequent lactation when compared to healthy cows. At the same time, only 66.9% of the infected cows at drying off cured from existing IMI. Unfortunately, whether or not infected cows managed to cure across the dry period, they struggled with udder health throughout the subsequent lactation and were at least twice as likely to develop clinical mastitis (CM) or to be culled when compared with cows that remained healthy across the dry period.
Test-day data before drying off were explored to evaluate their diagnostic ability to detect noninfected cows at the time of drying off in 15 commercial dairy herds with an adequate udder health management. We confirmed that SCC information derived via milk recording is capable of predicting the absence of IMI with major pathogens at dry-off, yet (an estimate of) the herd prevalence of subclinical mastitis, the cow’s milk yield and parity impact the estimates of the sensitivity, specificity and predictive values to some extent.
An SDCT algorithm was developed, including the cow’s test-day information and CM history prior to drying off. In total, 12 commercial dairy herds with a general good udder health, that previously applied BDCT, were enrolled. Within each herd, about half of the cows were selectively dried off without antimicrobials using this algorithm, and their performance was compared with the other herd mates that were dried off using BDCT. All cows received internal teat sealants at drying off. The CM risk, culling hazard, and test-day milk yield and SCC were not negatively impacted. Still, antimicrobial use for udder health, monitored from drying off until 100 days in milk, decreased significantly. We concluded that implementing SDCT to reduce the antimicrobial use on commercial dairy herds, using strict selection criteria and test-day information, is possible without jeopardizing udder health or milk yield.
Dr. Zyncke Lipkens (°15 April 1990) graduated as a veterinarian from Ghent University in 2014 and immediately started working on a PhD at the M-team / Mastitis and Milk Quality Research Unit from the Faculty of Veterinary Medicine at the same University, funded by IWT. She actively participated in the clinic of reproduction and obstetrics, in the lab of the research unit and obtained the diploma of the Doctoral Schools of Life Science and Medicine. She was one of the driving forces behind the establishment of Continuo, the alumni and staff orchestra of Ghent University.