Arguably the most significant health concern regarding dairy production is that of mastitis. By definition, mastitis is inflammation of the mammary gland of the cow. This inflammation is typically a result of invasion and infection of the mammary gland by bacterial organisms. When considering the strategic treatment and prevention of mastitis, bacterial organisms are commonly divided into two groups: contagious and environmental pathogens.
In this article, our focus will be on the contagious pathogens that cause mastitis and their effective treatment and control.
There are three primary organisms that are considered contagious pathogens causing mastitis in dairy cattle. These include Streptococcus agalactiae, Staphylococcus aureus and Mycoplasma species. Consistent with their classification as contagious pathogens, these organisms are adapted for residing primarily within the mammary gland of the cow and spread from one cow to another most often during the milking procedure as they gain access to the mammary gland through the teat orifice. Therefore, knowledge of these generalized characteristics as well as characteristics specific to each organism allow for targeted treatment and prevention strategies.
Strep. agalactiae is especially adapted to residing within the udder of the cow and does not survive well in the environment. In theory, if all mammary gland infections within the herd are eliminated, then the organism can be eradicated from the herd. This goal is reasonably achievable and economically feasible for most dairies. Strep. agalactiae should be suspected in cows with elevated somatic cell counts and decreased milk production associated with subclinical mastitis or a lack of obvious signs of infection. Culture of suspicious quarters can confirm or rule out infection. Staph. aureus is a primary culprit in chronically infected cows that appear to suffer from recurring bouts of mild clinical mastitis. Staph. aureus can be challenging to effectively treat and eliminate from the udder because it walls itself off within scar tissue and abscesses in the udder of the cow. Therefore, prevention and early treatment are key to controlling Staph. aureus mastitis. Mycoplasma is a less common pathogen and unfortunately does not respond well to antibiotic treatment. Ultimately, routine culture of mastitis cases provides the most accurate information as to the causative organism and aids producers in implementing effective treatment and control.
Since the majority of the transmission of contagious organisms occurs at milking time, proper milking routine and teat care are paramount in controlling contagious mastitis. Several basic procedures can help dramatically in reducing new infections. If possible, known infected cows should be milked last and culling chronically infected cows should be considered as a means of reducing exposure to healthy cows. Every teat of every cow should be thoroughly cleaned and an effective pre-milking teat dip should be used appropriately to minimize contamination of milking equipment and subsequent transmission between cows. Properly functioning milking equipment prevents teat injury and backsplash further reducing contamination of the mammary gland. According to the National Mastitis Council, a post-milking teat dip is the single most effective means of preventing contagious mastitis as it minimizes exposure of the teat orifice to bacteria after milking when it is most susceptible to invasion. Lastly, early treatment during lactation and the use of dry cow therapy at dry off, based on culture results if possible, can improve the chances for curing identified infections.
Darren Loula, DVM, is owner of Christian County Veterinary Service, LLC, a mobile large animal vet clinic.
