Necropsies.

 By Heather Smith Thomas.

 If an animal dies and the cause of death is unknown, it pays to do a necropsy to try to determine what happened, especially if a change in management could eliminate the risk for further deaths in the herd.

Dr. David Steffen, Veterinary Diagnostic Center, University of Nebraska-Lincoln, is a firm believer in the value of accurate recording of mortality.  “For large operations, it makes sense to have the veterinarian teach the basics of post-mortem examination to the herdsman, so deaths can be classified as respiratory, enteric (gut), nutrition or something else—depending on the production stage or age of the animal involved.  An accurate accounting of mortalities can flag problems and signal a need for review of health programs.  The necropsy serves as quality control for clinical assessments and treatment protocols,” says Steffen.

“The veterinarian’s role is in training and quality assurance for tracking the occasional mortalities, and for consultation when mortality numbers spike to a point where intervention is needed,” he says.  In these instances the veterinarian may need to help with adjusting the treatment and management protocols.

“If animals are dying, the producer needs to keep good records and know how many have died.  There’s a certain threshold for different production phases, for anticipated death loss,” he says.  “If you have records you can look at the losses in previous years and set a goal for improvement—or if it’s a low level you can try to maintain that low level,” says Steffen.  It’s good to sit down with your veterinarian who knows your operation and establish thresholds for when you need to take action.

“When things begin to go awry, and death losses are above normal, the next step is to categorize them as to body systems involved, whether it’s skeletal (like a fracture),  respiratory, or enteric (digestive tract) or something else.  Most people can characterize things as to whether it involves the respiratory system or is an enteric disease,” he says.

“There’s always regret when a dairy has lost their 5th cow and wants to know what’s going on.  We ask what they found with the first 4 and they say they didn’t do a necropsy on those.”  They’ve lost that window of opportunity to have a better idea of what might be happening.

Dr. Frank Garry (Department of Clinical Sciences, Colorado State University) says number of deaths should be noted, and a person should never just assume that some animals will die, without trying to find out why.  

The dairy industry tends to lose more animals than feedlot or cow-calf producers.  “We’ve spent a number of years determining why so many dairy cows die.  The dairy industry is complicated because we’ve bred these cows to be such prodigious milk producers,” says Garry.  This requires intensive feeding, fine-tuned nutrition, proper milking, etc.  These cows can’t go out in nature and take care of themselves.  They are expected to perform to a very high degree; the dairy system is based on maximum production, with many cows.

Garry started looking at statistics.  “Death rate in feedlots across the country averages about 1.5% and in the cow/calf industry the death rate in cows is lower than 1%.  We found many dairies with death rates of 8% or more in lactating cows,” he says.

There is no national statistic, however.  “Unless you do surveys or look at records, this is not a number that is monitored like milk production.  Each state has published data on milk production per cow per year.  There are also published records on reproductive rates, calving interval, etc. but you can’t find mortality rates.  Death rates have not been monitored closely in the dairy industry, but this is changing, due to research we’ve done,” says Garry.

Why Do Dairy Cows Die?
In feedlots the main cause of death is infectious respiratory disease.  “The feedlot industry knows which problems they need to focus on, but in dairy those statistics did not exist.  There is no national collection of data to allow a dairy operation to see where they stand, relative to other dairies,” says Garry.

A dairy producer might not know what the main problems are on that dairy, and therefore can’t correct the underlying reasons why deaths might occur.  “We felt we needed to do lot of necropsies and find out why cows die.  Along the way we looked at how many necropsies are actually done on dairies,” he says.

He works closely with people at USDA in Colorado who do NAHMS (National Animal Health Monitoring Surveys) that include cow/calf, feedlot, dairy, goat, sheep, pigs, etc.  “In 2014 we found that only about 4% of all cows that die on dairies are necropsied.  Dairies often make an informed guess and write that down in their records,” says Garry.  Later they might look back in the records and say a cow died from such-and such, but it was never actually confirmed as the cause of death.

“In our study we necropsied every cow that died, in several dairies.  We found some surprising things.  In the feedlot industry, we can say that 2/3 of all deaths are due to infectious respiratory disease, and the necropsy confirms it,” he says.

By contrast, in dairies there are many more reasons for death.  “We documented 32 reasons for cows dying, that we could easily define.  If there are so many different causes, is there anything we can do to prevent these?”

If dairy producers keep records on cow losses, those records might include respiratory, but we often don’t know what kind of respiratory problem.  “Was it upper respiratory (such as laryngeal) or a lung problem?  Was it really respiratory, and if so, was it infectious or some other cause of the respiratory issue?  If the record only says ‘Resp’ we don’t really know,” Garry explains.

Maybe the records say it was digestive, but that covers many things.  “Was it a surgery gone wrong, or an abomasal volvulus or a twisted gut or something else?  The record systems are not very informative.  If we have poor tracking of actual cause of death, and poor record information systems, we don’t actually know why the cow died.”  

If more than 3 or 4% of cows die each year, that’s higher than it should be.  “On a well-managed dairy it’s possible to get death rates down to 3% or less—and this is probably the historical norm.  In reports from the 1960’s and 70’s, looking at permanent removals from dairies, this was a typical target for death loss.  If a dairy has a low number for death loss, it probably means the management is done well,” he says.

On the other hand there are dairies with death losses around 10% and occasionally higher.  “Then we wonder if some of those might be preventable.  We find it wasn’t just a single problem that caused that increase; it’s a complex set of decisions and management applications that aren’t going as well as they should. Doing necropsies is the only real way to know why a cow died.” 

Without that information no one can make adjustments in management that might prevent the next cow from similarly dying.

Teaching Producers To Do Necropsies
“Veterinarians are not the only people who can do necropsies.  The feedlot industry does a lot of necropsies, partly because of how they train their employees—to recognize that an animal is sick, and to make sure they get treated promptly, and that they get treated appropriately for the disease.  If a person does necropsies, they can determine if it was a preventable death but treatment was applied too late, or that an animal’s death was preventable but it was the wrong treatment.”  Necropsies provide information you would not have otherwise, and there is something learned from each death.

“If you simply put a dead animal in the compost heap it is truly a dead loss.  You lost the cow and lost the opportunity to learn from it.”  When you necropsy the cattle that die, you not only get good at doing necropsies, but can learn a lot about what is normal and what is not.

The veterinarian can’t always come to do a necropsy; it needs to be done soon after the animal dies, at least within 12 hours.  If it’s 24 hours later you won’t have a successful outcome because tissues have deteriorated.  Garry encourages veterinarians to work with their clients and teach them to necropsies.  With the advent of cell phones, the producer can tell the veterinarian what is observed when the cow is opened up—what various things look like—and the veterinarian can answer questions.  The producer can also send pictures of the various tissues.

If the producer has done necropsies before, it’s fairly easy to notice things like abscesses, abnormally-colored organs, blood in a body cavity, etc. and it catches your attention because you know what’s normal.  “A person simply has to shift from looking at the outside of the animal to observing the inside, and will then be as good at picking up abnormalities as the veterinarian.  If you know what the abomasum looks like because you’ve seen it multiple times, when it doesn’t look like that, this is a clue,” says Garry.

“People in the dairy industry should be doing a lot more necropsies.  You don’t need to call the veterinarian every time.  If you are working as a team, the veterinarian can easily show you how to do necropsies.  The veterinarian should be involved, but when this isn’t possible, next best is to have you do it and send photos, or call the vet while you are doing it, to ask questions.”  The veterinarian can guide you through it.

Most folks who do many necropsies can determine cause of death in most cases, but there will be times they need veterinary assistance.  In dairies, especially, there can be so many different cause of death that sometimes it might be difficult for the dairy employee to figure it out.

When Do I Need A Necropsy?
Garry and colleagues did another study with several dairies and had them continue to keep their own records.  “We did necropsies on every dead cow and kept our own records; we necropsied about 100 cows and compared notes with the producer.  The producer was only correct (guessing the cause of death) about 50% of the time,” Garry says.  There were certain things in which producers were correct 100% of the time and didn’t need a necropsy because the cause of death was obvious.  Perhaps the cow was injured or was hit by lightning.  

There are other instances, however, in which the cow was normal yesterday and dead this morning and we have no idea what happened.  “In that situation we absolutely need a necropsy.  There’s also elective euthanasia; the veterinarian has confirmed the producer’s diagnosis and the cow is not responding to treatment and is suffering.  She’s had antibiotics and can’t be sent to slaughter, so she is euthanized.  That cow probably doesn’t need a necropsy because there has already been a good diagnosis.”

On a typical dairy a person might need to necropsy 30 to 60% of cows that die.  “We only need to do the ones where we have questions and are not sure what happened.  This would include things like a fresh cow that has ketosis and goes down, and does not respond to treatment.  Maybe you euthanize her or she dies spontaneously.  You might say she had metabolic disease, or had ketosis.  But why didn’t she respond?  What are we missing?  We have a diagnosis but it’s inadequate and doesn’t tell us everything we need to know.  Those cows should have a necropsy,” he explains.  

“Then we might find that the liver is yellow like butter and splits apart easily.  In that situation the cow not only had ketosis but also fatty liver disease.  She might also have chronic respiratory disease that was not noticed earlier.  Maybe she has erosions in the rumen, indicative of rumen acidosis.  Perhaps she was fed too much and developed multiple problems.  Now you have a complex situation and need to work back through it so that in future you’d know how to prevent it,” he says.  If all you did was say she had ketosis and died, you wouldn’t find out about the other underlying problems.  

Any animal that dies suddenly, without warning signs, should be necropsied, as should any animal in which the treatment did not resolve the disease you thought it was.

Using A Diagnostic Lab
The veterinarian may occasionally need to send blood or tissue samples to a diagnostic lab.  “Our team tried to determine how often the veterinarian can make a firm diagnosis in the field, based on what we call a gross necropsy—without having to send samples and wait for results.  Often when we take the animal apart, the answer is clear.  We felt that veterinarians can do this about 90% of the time, based on observable things at the time of the necropsy,” he says.

 “Out of the 100 necropsies we did in our study, we needed additional diagnostics only about 10% of the time.  If the producer is doing a field necropsy and needs more information and has a checklist of samples to collect--for mysterious cases—those can be put in baggies.”  You could get a piece of liver, a piece of heart tissue, and a piece of bowel, for instance, and place them all in separate baggies to put in the refrigerator.  Then you call your veterinarian, mention what you saw, and ask if you need more advanced diagnostics.  If the vet says it would be good to have some liver tissue, you’d have it, and could send it in today, or tomorrow, depending on what your vet suggests.

Worst case scenario would be if you decide you didn’t need advanced diagnostics and throw them all out, or didn’t take any samples.  Work with your vet and diagnostic lab to determine which tissue samples to take at the time of necropsy.  “Some are really key.  If you find a cow with severe pneumonia you’d want to take a piece of the diseased tissue.  You could submit it for culture, for virology, for microscopic analysis, for toxins, etc.” Garry says.  In some cases it is worth spending more money to send samples to a diagnostic lab.  If it’s an outbreak, it’s even more important.  If a cow dies today and another one dies tomorrow, you’d get more serious about pursuing the problem because you don’t want to lose more cows!

“What we are looking for are things we could change that would prevent this in the future,” says Garry.  Some things you can’t change and you can’t really prevent a future occurrence, whereas in other situations there are things you can change in your management.  That’s the value of a necropsy; it guides your management to find ways you might be able to prevent future incidence of loss.