What’s the big deal with aspirin?

I am going to apologize in advance as this article gets a little in the weeds when it comes to drug approvals. However, given the recent attention that the Food and Drug Administration has given to aspirin use in lactating dairy cattle, I wanted to provide clarity on the FDA’s recent communications.

The FDA is the main regulatory body responsible for approving and monitoring drug use in food-producing animals. Recently, veterinarians were sent a letter regarding the use of aspirin in lactating dairy cattle. The FDA clearly stated that they are aware that aspirin is being used to treat lactating dairy cattle for fever and pain and such use of aspirin is prohibited. Until now, the FDA has turned somewhat of a blind eye to aspirin use in lactating dairy cattle. Previously, the FDA had stated that aspirin was of low regulatory concern, so while its use was not legal, it didn’t appear to be a high priority for monitoring or enforcement. However, this is no longer true, and the FDA’s change of stance appears to be due to the rise in aspirin use with the spread of highly pathogenic avian influenza in cattle.  

So why is aspirin prohibited by the FDA? Despite its widespread availability, aspirin has never actually gone through the approval process for use in cattle. All FDA-approved animal products carry the statement “Approved by FDA under NADA/ANADA #XXX-XXX.” In fact, there are several other drugs used in animal health that do not have an FDA approval such as lidocaine, epinephrine and calcium solutions. You might wonder why these drugs don’t have FDA approvals. This can be typical of low-revenue products where companies do not foresee a significant return on investment in the expensive and sometimes lengthy FDA approval process.

How exactly is aspirin used on farms? I typically see aspirin used in two different scenarios. The first is for a sick cow that may or may not be culled; therefore, the producer does not want to administer drugs that carry a significant withdrawal period but may still want to provide some sort of supportive care. The second scenario is the widespread administration of aspirin in fresh cows after freshening to reduce inflammation and increase milk yield. Although several studies have shown potential boosts in milk yield following aspirin use, the follow-up work on milk withdrawals by Kansas State University is somewhat discouraging considering the FDA’s prohibition of aspirin. In one KSU study, researchers administered oral aspirin (3-5 boluses of 480 grain) to first lactation and mature cows after freshening and again 24 hours later.  Blood and milk samples were then collected to evaluate aspirin concentrations and used to estimate withdrawals based on FDA methods.

The study found that the previous 24-hour milk withdrawal guideline for cattle treated with aspirin may need revision to 156 hours for whole-herd treatment scenarios and 120 hours for individually treated cows. This data also found that aspirin appeared to mitigate prostaglandins, or inflammatory markers, for only 12 hours after administration.

Should we continue to use aspirin? At this time, I would say no. Due to its lack of official approval, the FDA has no established withdrawal and if milk was tested, the tolerance would be considered zero. The FDA does have the capability to test milk, though we haven’t had any indication that they plan to test or how they might implement such testing. If one decides to continue aspirin use in lactating dairy cattle, consider extending the milk withdrawal period significantly longer than 24 hours. Additionally, I would challenge pharmaceutical companies manufacturing aspirin to take the time and resources to finally seek FDA approval so producers can use their products with confidence knowing that they work and not have the liability of guessing at withdrawal periods.

So, what should be used instead of aspirin?  This is another potentially loaded question that producers should discuss with their veterinarian of record. If we follow the FDA-approved products available for cattle with specific pyrexia and pain labels, veterinarians and producers should be using injectable and pour-on flunixin options. Injectable flunixin should be given intravenously only. If IV administration is difficult to perform on the farm, there is a pour-on flunixin product available called Banamine Transdermal that is easy to use and has been approved in both beef and dairy cattle.  Another option might also include meloxicam when used under the direction of a veterinarian. 

Megan Weisenbeck is one of six veterinarians at Northern Valley Livestock Services in Plainview, MN. She practices primarily dairy production medicine in Minnesota and Wisconsin. Megan can be reached at [email protected].