by: Heather Smith Thomas

It's harder today to keep calves healthy after they leave the ranch and enter a feedlot. Dr. Eugene Janzen (Assistant Dean, Clinical Practice, Veterinary Medicine, University of Calgary) says there has been a lot of research in the past decades looking at pharmaceutics—vaccines and antibiotics. “The focus is often on demonstrating that one product works better than another,” he says.

“The results of this kind of research will probably hold true for a certain period of time, but not forever,” he explains. Producers will not be able to rely just on vaccines or antibiotics. It will be more important to address some of the management issues and some of the basic things we need to know about BRD.

“A project at Colorado State University has been looking at the incidence of BRD associated with accumulating groups of cattle and gathering them at auction markets. The primary factor in making cattle susceptible to BRD has been co-mingling, prolonged transit and multiple sourcing of livestock in an auction market system—and then moving them again, to a feedlot. Research has been comparing auction market derived animals at a feedlot versus those that just came straight from the farm,” says Janzen.

He feels it is important to study the mechanisms of BRD. “Two things have happened within my lifetime. We have developed some very good vaccines against Mannheimia, so it is no longer the primary bacterial pathogen causing BRD in some regions, for instance. So the other pathogens that now cause the majority of problems are various kinds of Mycoplasma,” says Janzen.

“There are many publications in the literature describing how effective the use of antimicrobials administered to every animal upon arrival (metaphylaxis) might be when animals come into the feedlot. Those two things — good vaccines against Mannheimia, and metaphylaxis at the feedyard — have made a huge difference, but have also created a new or different respiratory disease than we older veterinarians grew up with,” he says.

“One of the predominant pathogens that moved into this gap is Mycoplasma. The big question now is why pharmaceutical companies have not made a vaccine for Mycoplasma bovis. The reason they haven't is that it is not simple,” says Janzen.

There are new diagnostic tests for respiratory disease, and these can be helpful when trying to sort out the cause of a certain BRD outbreak, but some of the respiratory problems we are faced with today are more subtle and not as easy to recognize.

“We've gone from seeing acute bacterial pneumonia to seeing more chronic respiratory problems. Most of the cattle that die are suffering from a more chronic mix of pathogens. This is a lot different from what we were dealing with 40 years ago. When I grew up we could give a sick animal eight ounces of sulfamethazine and 10 ccs of penicillin and it got better,” says Janzen. Now respiratory disease is much more complicated and the traditional treatments don't work anymore.

“In earlier times, we could wean calves and watch them for about 10 days, or fill a feedlot pen with new cattle and watch them closely for four or five days, and then the epidemic curve was over. All you had to worry about was bloat or some other feed-related issue. Now it's not that simple, and incidence of respiratory disease can keep dragging on for weeks or months. As the vigilance in a pen diminishes, or the mix of pathogens increases, you see animals getting different kinds of pneumonia and some of them are harder to detect,” he says.

“The mycoplasmas for example do not produce a toxin, so those animals don't give us the benefit (for detecting it) by looking sick. The disease can be well advanced before we realize the animal has a problem. By contrast, in earlier days, there might be a pathological lesion in the lungs, and if it was caused by an aggressive Mannheimia, these individuals would be depressed; they were obvious,” says Janzen. In spite of advances in drugs and treatments, bovine respiratory disease continues to be a challenge. At least there are some new diagnostic tests for respiratory disease, and these can be helpful when trying to sort out the cause of a certain BRD outbreak.

“Another new thing that has attracted a lot of attention, but which has some of us old-timers a little uncomfortable is that now everyone in research wants to build a robotic cowboy—in other words, come up with new technology to help us determine when the animal might be sick. This is happening at many universities, and also here at our veterinary school; research is working on improved methods of detecting the cattle that are ill. But some of us old-timers are wondering how effective this would be. If the nature of respiratory disease has changed from what it was 25 years ago, to a disease with new pathogenic agents (and there are some indications that this is the case), occurring at a different time during the feeding period, then I'm not sure how appropriate this new technology will be,” says Janzen.

“There is some resistance regarding building a ‘pretend cowboy', using technology to monitor feed intake, water consumption, body temperature, etc. Some of this research has utilized weigh scales next to the water bowls so that when an animal comes up to drink—even if they just step on the apron with their front feet—their weight is calculated by an algorithm based on the weight of just the front two feet,” Janzen says.

“There is a lot of work in progress, looking at measuring to see whether we can tell earlier if these animals are sick, to see if the technology can do that better than the cowboy on a horse. There are also studies looking at putting sensors in the ears, or an infrared camera at the water bowl in an attempt to measure the animals' temperature when they come up and drink. Whether this is a direction we should go or not is a topic that has generated considerable discussion,” he says.

With labor shortages, it's harder to find good feedlot cowboys, especially people who are “tuned in” to cattle and good at picking up early signs of sickness, so some feedlots are interested in finding other ways to monitor pens of cattle. As technology progresses it will be interesting to see if the cost of these new methods will be low enough and the reliability good enough to bring some of these new techniques into general use.

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