THE CASE OF THE SNOWFLAKE: Understanding Disease Diagnostics

Solving a disease outbreak in a group of calves may require intense investigation. A veterinarian and producer often find themselves looking for clues and asking questions to point them to the culprits.

In my 28 years as a diagnostician the one constant I’ve seen is that disease cases are like snowflakes — each diagnostic case is unique.

I always tell cattlemen that it’s essential to contact your veterinarian immediately — before extensive treating and before the mortality rate goes up. From there, you can work together to determine what your goals are and what questions to ask.

You and your veterinarian might turn to diagnostic testing for answers, but without a few guidelines, you won’t be any closer to solving their mystery than when you started. Know what your goals are and what your diagnostic questions are.

Smart questions, smart answers                                                                                                                 When working on a diagnostic issue, I tell those involved the first step is to slow down and think about what questions can answer your goal for diagnostics:
• Where and how were the cattle purchased?
• How did the cattle look coming off the truck?
• Did they get vaccinated on arrival?
• Did they start eating as soon as they arrived?
• Are there ration factors to consider?
• Are there signs or symptoms of a virus circulating?
• Do clinical signs relate more to a bacterial infection?
• Is there a nutritional issue, such as a mineral deficiency?
• Could we have a BVD-PI in the group?

Once you know the diagnostic question you are asking, work together to come up with solutions for what’s going on. You’ll also want to determine if you are collecting the right tissues or samples to answer your specific question. Working with your state or regional diagnostic laboratories can be of great benefit to make sure the correct samples are collected.

If there are suspicions the issue is bovine respiratory disease (BRD), the veterinarian should conduct a postmortem exam to gather information. Your team also may decide to collect antemortem nasal or trans-tracheal wash samples for lab analysis.

A key to the success of these tissue diagnostics is to sample untreated animals if possible. Animals that have been treated may impact diagnostic results, particularly bacterial culture. If nutritional issues are a concern sample those animals that are clinically normal with liver biopsies. Sampling a clinically ill animal for evaluation of nutritional status may give the wrong impression of underlying factors.

Economic resources and goals are also a factor. For instance, the panel of diagnostics might be the most expensive part of a diagnostic workup. You and your veterinarian can evaluate if the cost of the test is worth the information the result will provide – is it economically feasible and will the information answer your key questions? You’ll want to choose diagnostic tests that will give you the most usable information for your diagnostic dollar.

Remember, taking samples doesn’t necessarily mean that you are delaying treatment or facing more losses. In many situations, your veterinarian may say we need to send samples to the lab to help determine what’s going on, but we are going to treat them now as well.

Management matters
But your diagnostic investigation doesn’t stop there. And it may not even start there.

The one thing to remember is that there may be a management component to your diagnostic question. Pathogenic organisms can exist in animals and never cause a problem. But management changes could potentially trigger disease.

Various factors, such as ration changes, unvaccinated calves and changing weather patterns, can work together to create a disease scenario. For example, a ration change can disrupt rumen microflora and stimulate a metabolism change. That same ration change tied with overcrowding, bad ventilation, storm systems and temperature variations can cause a BRD break.

Evaluating management questions and issues can help identify the correct diagnostic test and interpret the results.

Another scenario might find you dealing with a scours issue. You’ll want to remember to collect feces samples from acutely affected calves that haven’t been treated but also carefully consider the management factors influencing the group of calves. If you have a serious, consistent scours issue it might be caused associated with calving environment, cattle flow, ventilation, or sanitation. In these cases, its often not so much the agent, but how to break the cycle of exposure to the calves.

Variation of management practices and geography across the industry makes it difficult to establish an industry-wide standard operating procedure for collecting diagnostic samples because no question or corresponding answer will ever be the same.

It’s all up to interpretation
If tissues are sent to a lab, think about how the data will be used once it is received. Often the biggest errors are made in overinterpretation of that data.

It can be tempting to lock on to a positive result and assume it’s the problem. We want easy answers and something to blame. The reality is there are many factors impacting each case.

It all comes down to identifying your operation’s goals. Those goals will ultimately determine which diagnostic option will yield the most useful information.

My final piece of advice is to take the basic first step. Remember, if you have a problem, call your veterinarian now. Don’t wait, delaying involving your veterinarian can reduce treatment response, cost time, and money.
Article is an excerpt from previously published material in
Progressive Cattle August 2020.