Editor’s note: Third in a bovine lung immunology series.
There are various clinical signs feedlot cowboys use to assess sick cattle, ranging from snotty noses, depression and anorexia. But taking a closer look at those clinical disease expressions and understanding their subtle differences can give you a better clue as to what’s happening in the animal.
For example, Breck Hunsaker, DVM, PhD, Livestock Consulting Services and Horton Research Center, Wellington, Colo., says in an infectious bovine rhinotracheitis (IBR) study he conducted, cattle developed ocular and nasal secretions that were serous in nature. “My feeling is that once you start seeing mucopurulent discharge, you then have bacterial involvement that is expressing itself,” Hunsaker explains. “You may have had bacterial involvement earlier, but it was subclinical.”
Cellular debris containing neutrophils will give nasal secretions a greenish tinge. A drop in water content makes mucus cloudy and thick.
Depression also leads to a lack of grooming and the cleaning of the nostrils, so when you start seeing nasal discharge, this may be associated with depression.
But don’t get hung up on snot alone — a calf that is eating with no clinical depression or dull eyes but has a milky discharge may have a simple case of rhinitis or sinusitis, says Chris Chase, DVM, PhD, South Dakota State University. “For those of us who suffer through sinus infections, our lung capacity is just fine.”
For Kip Lukasiewicz, DVM, Sandhills Cattle Consultants, Inc., Ainsworth, Neb., if we could measure the feed intake of individual animals, we would see a decrease in their consumption as the first clinical sign. “Body temperature is still an important measurement, but I rely on it less in my assessment of clinical disease,” he says. “There are some animals that have a low temperature and are still sick. Depression and lethargy are clinical signs along with less feed intake, therefore, they may appear gaunt.”
Coughing can also be a clinical sign, but Lukasiewicz warns that you have to be careful when describing a cough to feedlot cowboys. “Otherwise you start having a hundred pulls. Coughing is also a normal defense mechanism. Even snotty noses can be normal. So you have to look at the depression level and the level of gauntness and that animal’s willingness to move among its penmates.”
Lukasiewicz believes prostaglandin may stimulate an infiltrative inflammatory response in the intestinal endothelium leading to absorption abnormalities, hypermotility and diarrhea. He explains to cowboys that it’s easy to see the animal in the pen with its head down and is deathly ill and probably 48 hours from dying. “If we’re pulling animals like that and patting ourselves on the back, I’m not really impressed,” he says. “I’m more impressed with the guy who can pick out an animal and the guy at the hospital asks, ‘What did you pull this animal for?’ and the cowboy’s response is, ‘He wasn’t grooming himself. His hair-coat was off. He was kind of stiff and slow when I moved him off from his penmates.’ Now it’s up to us in the hospital to determine is it respiratory, is it metabolic-digestive, is it a kidney problem, or what else is going on?” At this point, Lukasiewicz adds that temperature becomes a factor, and listening with a stethoscope is beneficial.
“Some of those things are very subtle and it gets back to sensitivity of your penrider,” Chase agrees. “But the loss of appetite — that’s the tip-off.”
Phil Griebel, DVM, PhD, Vaccine and Infectious Disease Organization, University of Saskatchewan, says there can be a disconnect between the severity of clinical signs and the severity of a respiratory infection. “In our experimental challenges, we observed very acute deaths. There was a clinical veterinarian observing the calves every four hours and doing clinical scores. Even though the clinical scores were quite low, the animals could be dead four hours later. You can blame the penriders, but I also think there can be a disconnect between the clinical symptoms and the systemic inflammatory response that’s going on in those animals. Clinical symptoms are not always going to be commensurate with infection.”
“It’s one of the reasons why sometimes the person doing the necropsy is blinded by all that clinical performance because you have preconceived notions,” adds Dr. Scott McVey, DVM, PhD, Veterinary Diagnostic Center, University of Nebraska. “It biases the judgment.”
Hunsaker concludes we’re not as smart as we think we are when detecting clinical signs for a couple of reasons. “Look at lung lesions at slaughter versus their treatment history. A high proportion of cattle — something like 35% — never saw the hospital and were never treated therapeutically.”
What’s interesting is in the same population of animals, there can be strikingly different gross findings. “Why is there such a dramatic fibrinous response in one, where in another it’s more of an interstitial pattern?” Hunsaker asks. “Is that because they were more susceptible at the time when the agent was more prevalent? Do they have some level of immunity to one agent and less to another? All of these questions are fascinating when you crack that ribcage and start looking for differences.”
And there can be differences even within the same lung. From the standpoint of looking at antimicrobial sensitivity testing and building of antibiotic resistance, how many bacteria are in that lung in a well-developed case of pneumonia? McVey studied a large num-ber of fairly acute deaths and looked at central lesions, peripheral lesions and airway-centered lesions, then quantified all the bacteria in that tissue. “There was anywhere from around 103 bacteria per gram to 108 bacteria per gram,” he says. “You take a 20-kilogram lung that has about 60% consolidation and you multiply that out by how many grams of tissue and how many bacteria are in that lung, and it’s a huge number of bacteria. You’re way above spontaneous mutation and things that might be happening in that bacterial population.”
McVey says around the airway, you tend to see a mixed bag of bacteria — more Pasteurella multocida, some Histophilus somnus, whereas if you get into the tissue, the center tends to be more Mannheimia-dominated. “We’re assuming these are early, but that could vary. Even within a lung, the patterns will be quite different. I think the vast number of these are probably polymicrobial, and I haven’t even talked about potentially some anaerobes or Mycoplasma that get in there, also.”
What do temps really mean?
For years the main diagnostic tool on the feedlot has been a thermometer along with observation. “I have witnessed 8% case fatality rates of animals that had temperatures of 101.5°,” notes Lukasiewicz. “How many veterinarians or consultants have a treatment protocol that states if an animal does not temp 104° or higher, you don’t treat him? I have pulled temp case fatality rates that will demonstrate a 101.5° temperature and I have an 8.3% case fatality rate. If that’s our main diagnostic tool, whether we treat or not, I think it’s ridiculous.”
Lukasiewicz says Australian veterinarian Kev Sullivan has done some work monitoring body temperature of feedlot cattle for 24 hours. “He’s demonstrated that some of those animals will have a 104° temperature through the entire feeding phase. At slaughter, the lungs are perfectly fine. I understand that for research, you have to have those standards, because it’s just part of protocol, but I think we need to equip ourselves with better diagnostics chuteside to have a more predictable outcome of our treatments.”
Chase has seen similar circumstances. “We did a study with a group of calves and they all temped 103° all the time. There were 40 head of animals and we couldn’t get them below 103°, but there was nothing wrong with them.”
Griebel explains the sometimes discrepancy in using temperature as an indicator. “The problem is that temperature doesn’t discriminate between a purely viral infection, which may not be life-threatening, or a secondary bacterial infection. Both of those infections can induce very high fevers but antibiotics will do nothing for the viral infection.”
Lukasiewicz wonders if some of the animals that don’t temp very high end up dying because of their own immune system or inflammatory response eliciting a poor response to the virus or bacterial infection. Hunsaker believes it could be the timing of taking the temperature. “That’s a point-time observation and that’s where we get hung up,” Hunsaker say. “If you’re not there when that’s happening, you miss it. We don’t know if we’re on the front end of the curve or the back end. But it’s really the only objective clinical measure we have.”
With a pure endotoxin challenge, McVey says you get a bi-modal bi-phasic temperature response. “If it goes up, then it goes down, especially as they proceed into hypovolemic shock stages. From doing several Mannheimia, Pasteurella, andHistophilus challenges, I find that it’s almost not worth checking temperature on those animals. You get the non-vaccinates and with some of them, the thermometer will never bump. Then you open them up and the lungs are a big mess.”
Hunsaker notes an observation exercise with students by Dee Griffin, DVM, MS. “As I recall, they ran a pen of cattle that weren’t showing any clinical signs through the chute in the morning and the afternoon and temped them. A number of those animals would have warranted treatment if that was the only criteria. Rectal temperature alone, as treatment criteria, was meaningless.”
Scoring sick cattle
Quantifying clinical signs is used in many research trials, and is a tool some feedlot veterinarians encourage feedlot crews to use. “When we review a research protocol for a respiratory disease study, there’s substantial detail in describing clinical illness,” Hunsaker says. “We have a clinical illness score of one. What does a one mean? What does a two mean? It’s difficult to put into words.”
Hunsaker’s clinical illness scoring is simple. A zero is considered normal. “In the early morning when it’s cold, you expect a discharge,” he says. “If it’s a 1, it’s a serous discharge but it’s more substantial than you’d expect and maybe there’s some ocular and some oral discharge that goes with it. If it’s a 2, it’s cloudy and that suggests a bacterial component. We’ve progressed beyond where we really ought to be to get them pulled and treated.”
One of the things Hunsaker likes to do is coach the cowboys to watch a pen from the outside prior to riding into the pen. “When you ride through it, the cattle brighten up.” Hunsaker is also working with some of his clients to do some clinical illness scoring. It helps us get to some of those pulls earlier, and timing is very important.”
Lukasiewicz notes that when those animals do get to the hospital, all of a sudden they’re in an unfamiliar place, away from their penmates. “That makes them uncomfortable and they might even try to convince you they’re okay.”
“It’s a different depression score than you saw 10 minutes ago,” Hunsaker adds.
Lukasiewicz tries to teach hospital crews not to just observe an animal, but to communicate with the cowboy to understand why the animal was pulled. “That cowboy has the ability to clinically score that animal, and that helps the person in the hospital.”
Depression and weight
Defining depression in cattle is very subjective because depression is relative to what we know as normal behavior for each animal. “That’s why we’re able to detect depression in an animal if it’s slow coming off the bedding pack, if it’s not joining the group,” Griebel explains. “When we do it experimentally, we have small groups and we know those animals, so it’s easy for us to tell when an animal has changed its behavior. When you’re in a pen of 400 or 600 animals, the penrider can’t know all those animals individually and it’s much more difficult to detect depression. It takes a trained eye.”
But relying only on depression is tricky. Griebel says a veterinarian in an experimental trial euthanized calves because he said with their level of depression, they were going to die within 4 to 8 hours. “We performed post-mortem exams and observed a very low level of lung pathology,” Griebel says. “Clinical symptoms can be much more severe than what’s really going on within the animal. You can also have very severe depression and loss of appetite, and it doesn’t match with what’s going on in the lungs.”
The other criteria we use is weight loss, Griebel adds. “It’s a very important measurement and having a scale at the chute is an important tool. In experimental infections we see loss of appetite. Those calves that aren’t going up to the feed bunk are animals that really need to be watched. A scale doesn’t help the first time the animal goes through the chute, but as it comes through for a repeat treatment, you’ll note a loss of weight and maybe a very serious problem in that animal.”
Hunsaker agrees that weight loss is probably a better indicator than rectal temperature because it’s more sustained. “In a study reported by Shawn Blood, DVM, he looked at whether they maintained their weight, whether they gained 5% or more of their body weight or lost 5%, and then what their risk of being re-pulled was,” Hunsaker says. “I believe it suggested that body weight change post-therapy is probably a better objective measurement than rectal temperature.”
Next: Prevention and treatment of BRD
This information is from a Bovine Veterinarian roundtable sponsored by Schering-Plough and moderated by Jessica aurin, DVM.