Mastitis is an everyday concern on most dairy operations. The costly consequences of intramammary infections include lower milk quality and yield, premature culling and reduced reproduction efficiency. When it comes to treating clinical mastitis, blanket antimicrobial protocols are common. But before automatically reaching for the nearest mastitis tube, consider how a more strategic approach to treatment might reduce costs and improve outcomes.
To get started, ask yourself these five questions when making clinical mastitis treatment decisions.
1. How severe is the infection?
Evaluating the severity of mastitis cases can help inform treatment decisions. Clinical intramammary infections can be categorized as follows, based on the cow’s symptoms:
- Mild clinical: A cow has abnormal milk, but the cow and udder are otherwise normal.
- Moderate clinical: Abnormal milk and visible udder inflammation are both present.
- Severe clinical: A cow has abnormal milk, visible udder inflammation and signs of systemic illness, such as fever, dehydration, being off-feed or having an overall poor appearance.
Of the three categories above, mild clinical and moderate clinical cases are often referred to as “nonsevere” clinical mastitis, as they lack systemic signs and are localized to the mammary gland. Most cases of clinical mastitis in today’s dairies can be classified as nonsevere.
Understanding infection severity gives you the opportunity to make strategic decisions regarding intramammary antibiotic treatment versus the traditional standard of treating all cases of clinical mastitis (i.e., to treat or not to treat).
2. What is the cow's history?
Recordkeeping is essential for making cost-effective mastitis treatment decisions. Knowledge of an individual cow’s past udder health status can provide clues as to whether treatment is warranted.
Cows with no history of chronic intramammary infections are good candidates to treat with intramammary antimicrobials during lactation, regardless of their number of lactations. If a cow has a history of high somatic cell count (SCC), it would be appropriate to individually sample and milk culture these cows for bacterial isolation. For cows with recurring clinical mastitis or chronically elevated SCC, thoughtfully consider how to best manage these animals and whether they should remain in the herd or be removed.
When making treatment choices, especially in cases related to potential culling decisions, consider the cow’s age, milk production, stage of lactation, pregnancy status and other health events (such as lameness) that might impact her value and longevity in the herd. If a cow is low-producing, open or lame, it may not be profitable to treat her for clinical mastitis.
3. What is the cause of the infection, and what is the likelihood of curing it?
After determining that the affected cow is a candidate for treatment, knowing the pathogen is the best way to select an effective therapy. Keep in mind that not all mastitis-causing bacteria require antibiotic treatment. Milk culturing can provide insights into bacterial causes of mastitis, guiding the selection of appropriate intramammary antibiotic intervention. Research shows that delaying treatment for 24 hours while you obtain culture results will not impact outcomes for nonsevere clinical mastitis cases.
Gram-negative bacteria, such as E. coli, are responsible for 25% to 35% of intramammary infections. Mild to moderate gram-negative cases often spontaneously self-cure without treatment. The response to antibiotic treatment for these types of bacteria can be variable, and antibiotic treatment does not improve cure rates. An exception is Klebsiella spp., which has a lower spontaneous cure rate than other coliforms. Treatment may be warranted to increase the cure rate for Klebsiella spp.
Another 25% to 35% of mastitis cases are caused by gram-positive bacteria, such as Streptococcus uberis, Streptococcus dysgalactie and non-aureus staphylococci. Research supports treating these cases with antimicrobials.
While variable, 40% of mastitis cases that are cultured result in “no growth,” meaning that the bacterial cause is inconclusive. Research shows no benefit to treating these cases. Often, no-growth results are gram-negative bacteria and have a high chance of spontaneous cure, or they could be nonbacterial pathogens such as Mycoplasma spp., which are not susceptible to commercially available antimicrobial products.
4. What are the costs of treatment?
The price of the antibiotic tube is just one factor impacting the ROI from mastitis treatment. One must also consider both direct and indirect costs.
Keep in mind that nonsalable milk is one of the biggest direct treatment costs. When choosing mastitis therapy, give strong consideration to minimizing the amount of discarded milk associated with a treated case. Consider the duration of treatment and number of doses, as specified on the label, as well as the required milk withdrawal time and the lost value of the discarded milk.
Regarding duration of treatment, consider the concept of a bacteriological cure (bacteria no longer present) versus a clinical cure (milk is visually normal). Abnormal milk associated with mastitis is the result of an inflammatory response from the immune system. This inflammatory response (abnormal milk) can vary in its duration, independent of causative bacteria’s continued presence.
Most treatable bacteria associated with mastitis are effectively reduced at the initial labeled dosing, achieving a bacteriological cure. While the bacteria can be quickly treated effectively, the inflammatory response (abnormal milk) resolves more slowly. In most cases, extending the duration of therapy to align with the milk becoming clinically normal is not required and only extends the period of milk discard and drug treatment cost.
5. Does treatment support responsible antibiotic use?
Demand to justify the use of antibiotics in food-producing animals continues to increase, and the treatment of mastitis falls within this scope. An intangible cost of mastitis and its treatment is the potential loss of consumer trust if products are not used responsibly.
Judicious use of antibiotics, in consultation with your herd veterinarian, is a foundation of consumer trust – and required by law. Focus on the strategic treatment of mastitis cases with a high chance of success, and utilize judicious use of an antibiotic to address the underlying bacterial cause. Use antibiotics responsibly by following veterinarian-prescribed protocols and adhering to labeled milk-withdrawal periods after treatment. With any mastitis product, always read and follow label directions.
We, as dairy caretakers, often feel an immediate need to do something in response to seeing abnormal milk. However, it may be more prudent to pause, take a strategic step back and weigh the options before proceeding with blanket treatment for all clinical mastitis cases. Consider the questions above and talk to your herd veterinarian about strategic mastitis treatment plans that meet your specific operation goals.
References omitted but available upon request by sending an email to an editor.
