Editor’s note: First of a three-part series.
Chronic cattle in the feedlot are a problem on many levels. While sick, they don’t perform well, they cost money in treatment and labor, they may die, and there are welfare issues associated with their presence. But not everyone defines a chronic the same way.
“We consider chronics as the ones at a point where they will no longer gain weight at an appreciable level,” says feedlot consultant Kynan Sturgess, DVM, Amarillo, Texas. “We’ve treated them enough. They may not die, but they won’t gain. If they do, it will be at a rate that is not even close to being economically feasible.” Sturgess says this designation is not necessarily based on a set number of treatments because sometimes people put a false ceiling on treatment number. “We’ve seen animals that have had three to four treatment regimens that still feed out. Maybe not at the most economical level, but they will be close to going out fat with the rest of the pen.”
A chronic may also be defined in economic terms, says Doug Hilbig, DVM, Hilbig Veterinary Services, Lakin, Kan. In some situations, the number of treatments or the amount of money spent defines a chronic. Some of that may have to do with ownership -- if they’re owned by the feedlot, corporation, or individual customers. “Some will say when the cattle reach a certain point, the owners want a way out.” Hilbig notes that the industry has moved from the past strategy of hitting $70 or $90 in treatment costs, designating the animal as a chronic and getting rid of it. “Economically, that’s turned out not to work as well.”
While the definition of a chronic is pretty consistent across the feedlots that he works with, Shawn Blood, DVM, staff veterinarian for Hitch Enterprises, Guymon, Okla., says the decision of what to do with them can be different across operations, depending on ownership. “We generally define a chronic as an animal that has completed an established number of treatment regimens,” he says. “We make a decision after that as to whether we’re going to rail that animal or whether he can go back to the general population. We have to consider who the owner is and what his perception is of what we need to do with them. That all factors into the decision-making process. We do have a defined box we put those animals in with the ability to change that perception if management or owners deem necessary.”
Scott MacGregor, DVM, MS, Livestock Consulting Service, Idaho Falls, Idaho, says chronics seem to be at a low level as it relates to treatment response past three treatments. “We’ve gone to a protocol where if animals receive metaphylaxis, they will receive two other treatments,” he says. “If they have not received metaphylaxis, they will receive three treatments through the hospital. Then, they go to a low-density trap area and are analyzed for future economic value. Many are restarted. They may go on as a railer, and occasionally they’ll be sold back to a sale barn.”
From a diagnostic perspective, Robert Sprowls, DVM, PhD, Texas Veterinary Medical Diagnostic Laboratory, Amarillo, says, “The chronics we see have had a serious illness; they have failed to respond and they have not died. They don’t appear as if they’re going to go ahead and make a feeder. In the chronics we see on necropsy, usually over 50% of the lung is damaged to the extent that it will never recover.” Sprowls adds that it’s typical to find an abscessing pneumonia and, in some instances, a smoldering, chronic, active pneumonia.
How many are there?
On one hand, we transport cattle farther than we ever have, they often get commingled and exposed to a variety of diseases, and their stress level may be higher. On the other, today’s vaccines and antibiotics are better than they have ever been and nutrition is top-notch. So, has the level of chronics increased or decreased?
Hilbig believes his yards have remained fairly static. “In certain yards it’s gone up, but it’s because they’re feeding a totally different animal,” he explains. “Some of the yards that didn’t feed the high-risk, potential-problem cattle have had their rate go up, but it’s because they’re not feeding the same type of animal. They’re not feeding just yearlings or green-pasture cattle -- maybe only 20% -- and those cattle stay the same.”
For MacGregor, the number of chronics has increased as deads and percentage of deads, and he sees about .75 realizers for every dead. “Our definition has changed because over the last four years we’ve tried some new things that have helped salvage chronics toward re-feeding. We’ve been able to reduce the death loss.”
There’s a difference between feedlots, says MacGregor. If you want fewer deads, you can realize more. If you want fewer realizers because you don’t have the opportunities and options, then deads will increase. “In a perfect system, there should only be digestive and sudden-death deads. In that system, they go through the three-treatment program. You’ve modeled it so that most of the morbidity is up front, and they go into the traps. If they look like they’re going downhill, then you realize them, and if they don’t, you restart them. Obviously, we don’t attain the perfect system very often.”
Sturgess has a difficult time lumping chronics together from one yard to the next because of the variation in operations. Every other year he does a survey of high-risk cattle that looks at morbidity, mortality and treatment costs. It’s impossible to do across more than one organization because everyone has a different system. From one system to the next, you can’t compare medicine costs versus processing costs. “We have to look at a total, because one place will include metaphylactic costs into the processing program and the next one will include it in the medicine column. I’ve tried for a long time to get a feel for where chronics stand in importance, but all you can do is evaluate them one yard at a time.”
Impact on the feedlot
Like many health issues, on a day-to-day basis chronic cattle may be more important to the veterinarian than to the operation. Sturgess says on a scale of one to 10, chronics are about a three for a feedlot manager. “His priority will change as his number of deads per day changes. If he’s gone through a wreck and now they’re starting to die, it gets to be a lot higher priority, which is really the point where you’re not going to be able to do anything about it. It’s our job as veterinarians to make it a higher priority.”
Blood agrees that it’s pretty low for his managers as well, but the reason for that may be that chronics are a manifestation of treatment failures and high morbidity. “So, the manager is looking at morbidity and probably associated deads in there. He may be concerned about some of the things that caused those chronics, however.”
MacGregor adds that managers may blame the health program for creating chronics. “The manager won’t see a second-therapy case that dies; he’ll see a chronic. He has more feed, drug and labor costs in them, so the health program is suspect based on high chronic respiratory death loss. I get that at half my yards, especially from January through April as these chronics start to die. The manager says he has too many chronics, so to him the whole program downstream from that is suspect. To a certain extent, he’s right, but he may also be the one who doesn’t always want to do what you recommend for chronics. He lets them die rather than realize them. He’s got a huge farm, but he doesn’t want to fence some of it off for a trap to keep them going.”
Why do they occur?
Sprowls believes there are three basic reasons an animal becomes chronic: calves are pulled too late, are not given enough antibiotic long enough or are not treated with the right antibiotic. “Calves must be pulled early enough to avoid significant lung damage and administered the correct dosage of a good antibiotic.”
Failure of an animal to respond with the production of antibody against invading organisms is a significant issue. Whether it is poor nutrition, inadequate nutrition, poor genetics or whether they have been exposed to an immunosuppressive virus, each animal has to have a functional immune system to successfully fight off the infection.
MacGregor agrees that low immune response and high exposure can be forgotten variables, along with parasite load, poor management and late detection. “We’ve noticed that chronics tend to chase morbidity. The higher level of morbidity we have, the higher number of chronics. We tend to see more calves that go into the chronic category than we do yearlings because the morbidities are higher.”
There’s more to chronics than just focusing on antibiotics. Of the animals that get railed, Blood says about two-thirds are sold as chronic respiratory disease and another 30% is usually musculoskeletal. “We focus our attention on those major diagnoses, then backtrack. We look at the epidemiological triad of animal factors, environmental factors and pathogen factors. Then we look for weak spots in our system. We know by experience that if you focus on just antibiotics alone, you’re fighting an uphill battle.”
A higher number of chronic cattle may stem from seasonal issues, as well. In the Northwest, October and November and sometimes the early part of December are months with a high number of first-line pulls. Some cattle then move into the second stage, which would be relapse pulls, at which point the perception is that the treatment response goes down. “Now, we’re in the chronic stage and dealing with the fallout of the previous stages,” says MacGregor. “That tends to transcend through the winter and gets worse as the winter goes on.”
Cattle are not the same as they were 10 or 20 years ago. Conversion is up, we’re feeding a hotter ration than we were a number of years ago to lighter animals and yet morbidity and mortality don’t appear to have changed. Sprowls notes that with all of the newer antibiotics and better vaccines, you’d expect morbidity and mortality to go down. “Some people would argue in either direction, but our conversion is better and I think we have a larger number of pathogens and varied genetics in the pathogens, BVDV in particular. So if you stop and look, maybe we’re not doing badly at all.”
It’s not all incumbent on the cattle to just have a healthy immune system. The “human factor” is pretty good at messing just about everything up. “We tend to manage our way into 75% of our wrecks, and it’s usually from system overload, trying to do too much all at once,” admits Sturgess. “I have some customers who get upset when I keep telling them they’re overcrowded, but they don’t do anything about it.”
Hilbig adds that it’s a balancing act between personnel and their jobs. “Sometimes you just don’t have enough people to manage your environment and circumstances.”
Hospital pen as a contributor
The hospital is a big problem for many feedlots and contributes to morbidity. Blood says the home pen is always a better place for a calf because hospital pens tend to be small, overcrowded and have poorly managed feedbunks. “It’s an afterthought,” he says. “They are small, hard-to-clean pens, so you don’t have a tractor and scraper come through on a regular basis. We try to put more hurdles in the process of the failures, and some of them work and some don’t.”
MacGregor agrees that ranch calves especially don’t belong in the hospital. “It’s the best place to get sick,” he says. “One option is sending calves through at a run, give antibiotic therapy and they go home where pecking order, rations, density and exposure are all what they are accustomed to. Another, which you can do only if you own all the cattle, is to start a new pen of treatment cattle, which is something you see more overseas. They feel it reduces the relative density of the home pen, which is a positive, and it puts them with others who have a strike against them. They’re competing at the same level. On paper, there are advantages to both, but we surely don’t want them in the hospital, especially commingled with yearlings.”
Immune response to disease
Chronic animals fail to respond to treatment, and that means the immune system isn’t working. “If a set of cattle has a good, strong immune system, you can expose them to the same pathogens sale-barn cattle get exposed to, and they’ll do OK,” says Sturgess. “But you can also take those ranch-raised calves that have supposedly been raised just right and have been vaccinated, and you’ll wish you had bought sale-barn cattle instead.”
We can’t always control exposure, but we can try to manipulate immunity. “We’ve invested more money in the last five years in booster programs,” says MacGregor. “We’ve formed a fairly good database in Colorado where we looked at tens of thousands of calves that had been pre-conditioned plus tens of thousands that had been warmed up prior to entry to the feedyard. The pre-conditioned calves received all of their vaccinations at the ranch, in many cases from good ranches with good genetics, bulls and feed, and the calves still got sick. There’s no clear cause-and-effect relationship. There does appear to be a fairly high return to backgrounded calves that have been warmed up somewhere first for at least 45 days. They are notably healthier.”
It’s important to note, adds Sturgess, that backgrounding has also “weeded” out the weak ones, so they don’t ever make it to the feedyard.
Blood agrees that there is no control over exposure at the feedlot. “We try to focus on the immune system, but there’s so much that happens before that animal gets to us,” he says. “We have to start working on the immune system at birth and even as early as when the bull is turned in. I think there is a genetic component. I don’t have any numbers in cattle to support that, but we’ve done some sire studies at Hitch Enterprises’ pork research barn that show sire-line influence very clearly. We see as much as 2% to 3% mortality difference in a finishing situation. So I do think there is a genetic component, but I’m extrapolating that from the pork study. There’s so much that we don’t have control over pre-feedlot that has an effect on that immune system.”
Underlying deficiencies can be a culprit in a poorly functioning immune system. “In some cattle we’ve not known if they’ve had any kind of a PI BVDV problem in the herd, or if they’re out of very copper-zinc deficient areas,” says Hilbig. “That’s a challenge. Those cattle are healthy as can be and come in looking nice, but there is a problem with copper and zinc.” Sturgess adds that some cattle coming out of heavily populated sheep areas may only have access to low-copper (25 ppm) mineral blocks, which isn’t a high enough level for cattle.
Those calves with a suboptimal immune system or exposure to disease then start getting sick around 21 days on feed and they never stop. And, if you look at the titers on those acutely sick calves, says Sprowls, even though they’ve had multiple vaccinations, they will only have nominal serum neutralizing titers.
A pathogen party
It’s not that hard to pick out the typical chronic animal that has been sick and through rounds of treatment. Tipped over, long and bad haircoats are a giveaway. What MacGregor would like to know is can you identify the potential chronics ahead of time? “The best-looking ones get sick,” he says. “You could argue historically from databases that auction-market, commingled, numerous-origin calves less than 500 lbs. with morbidity rates to 75% create a lot of chronics.”
Diagnostically, the chronic picture is an interesting one. Sprowls suspects that multiple pathogens, viral and bacterial, are involved in producing a chronic animal. The re-pulls and chronics he sees have a significant number of pathogens, such as Mycoplasma, Pasteurella multocida and Arcanobacter pyogenes, but usually at that point the viruses are gone. Sometimes he’ll find an acute BVDV or acute IBR superimposed on a chronic state, or a reinfection of Mannheimia hemolytica as the cause of death. “They appeared to be stable, but when a new infection is superimposed over the old one, death usually ensues rapidly.”
Often a lack of previous antigen exposure is to blame. “Calves come in naïve,” says Sprowls. “They’ve had no or a limited exposure to major respiratory pathogens. Naïve calves are likely to have high morbidity/mortality and a high number are chronic.”
Some loads of calves have little or no illness with titers at 40 days showing no viral exposure other than probably vaccine exposure. Other loads will have a high morbidity and high mortality, and will usually have significant titers to multiple viral agents. “Different groups of calves come with different viruses and bacteria with varying degrees of potential to produce disease,” says Sprowls.
BVDV can be particularly troublesome. Animals that get exposed to a highly virulent BVDV will require a considerable period of recovery time before their immune systems are back to normal. “In some sick calves, we can isolate BVDV for extended times -- 30 to 40 days -- but then they clean up,” notes Sprowls. But as long as they are actively infected with BVDV, they are immunocompromised and spreading the virus.
Hilbig agrees that you don’t necessarily have to have a persistently infected BVDV animal to spread the disease -- a transiently infected BVDV infection that goes on for an extended period of time can also infect other cattle. Sprowls believes if BVDV could be reduced or eliminated, morbidity, mortality, re-pulls and chronics would be significantly reduced. “Usually when we zero in on a pen that’s having problems, we’ll find BVDV if we look hard enough. Or, we find very high BVDV titers that would suggest something more than vaccine exposure. I am convinced BVDV plays a huge role in the majority of adverse health scenarios in cattle.”
Mycoplasma is a different story. Sprowls doesn’t believe Mycoplasma is a primary pathogen in chronic feedlot cattle. “Once we get into heavier and older calves, Mycoplasma is an incidental or a secondary pathogen. Of course there are always exceptions,” he says. It’s not unusual on transtracheal washes on acute pulls on newly-arrived cattle to culture Mycoplasma. “On our multiple-origin cattle, it’s almost always present. But we’ll also see these chronic abscessing lungs, and the only thing we culture sometimes is large numbers of Mycoplasma.”
When Sturgess cultures acute cases versus chronic cases, there’s a substantial difference in the number of those cases that are positive for Mycoplasma. He wonders if it’s because they survived the treatment program. He’s made those observations through occasional studies where he cultures every dead.
Salmonella can also be ever-present. Sprowls often finds a high incidence of Salmonella when culturing stool samples from problem pens. “I don’t know what comes first -- the chicken or the egg -- if Salmonella was in the pen or brought in with the cattle,” says Sprowls. “It appears to be more problematic in immunocompromised cattle.”
Sprowls explains that on most of those operations; cattle are received in the same pen initially then moved to pasture. “Pathogen build-up occurs as we receive larger numbers of cattle into the same pens in a short period of time. On some premises you can isolate Salmonella from water, feed bunks and almost everything. The same principle probably applies to the larger numbers of cattle going through the marketing chain at this time. Pathogen build-up may play a role in this sudden change in animal health.” He adds that you’ll almost always find BVDV and Salmonella together.
Often at necropsy, Sturgess sees some type of enteric component, but because the digestive tract decomposes so much faster than the rest of the animal, it is difficult to get a good assessment. “It’s rare to catch those animals when they’re fresh,” he says. “We’ve focused a lot toward preventing enteric problems, particularly coccidiosis.”
Every feedlot is different, every manager is different, and every routine is different. What will work well in one feedlot will not necessarily work well in another. “It’s the consultant’s job to find the answer,” says Sprowls. “Everyone is still tweaking to optimize and figure out how we can do a better job.”
The big picture indicates that current modern feeding practices are counter-current to health, and “we’d better get over it because it’s probably not going to change,” sums MacGregor. “Feedlot operators have sacred-cow economic practices, and they’re asking us, as veterinarians, to not interfere with the cattle too much in those areas. New products, new technologies, imaginative management strategies for the hospitals -- all of those things are our responsibility. With all the new drugs and antibiotics we have, it is discouraging that their health isn’t getting better, but I think it’s understandable. Chronics are following the trend. As deads go up, so do chronics. We need to research areas such as looking at performance past treatment in terms of weight gains and carcass merits. There are still questions needing answers.”
Multiple failures tip an animal from healthy to chronic, adds Blood. “They failed to manage the immune system, maybe even as far back as failing to get colostrum into the calf. Then when we get him, we’ve failed to keep him from getting sick. We’ve failed multiple treatment regimens, and then we get a chronic or a dead animal. We like to go as far back as we can and assist clients by making a list of factors we don’t have control over, a list of those we do have control over, and then focus on those.”
This information is from a Bovine Veterinarian roundtable sponsored by Pfizer Animal Health.
Next issue: Treatment of chronics, BQA and welfare issue
DOES TYPE PLAY A ROLE?
Are some types of cattle more prone to become sick and, as a result, a potential chronic? Kynan Sturgess, DVM, tends to see problems in heavily exotic crosses and calf crops heavy in Simmental genetics. “I don’t know if it’s so much breed-related, but maybe more husbandry-related because they haven’t tried to utilize the benefits of heterosis,” he suggests. The straight Hereford herds out of New Mexico usually represent a significant challenge. “I don’t know if it’s a matter of breeding, but the fact that they haven’t changed animal husbandry practices in several generations is a problem. But at the same time, we’ll see other groups of calves breaking just as hard. Any time I see a group of really large-framed Simmental-cross calves, it scares me.”
Doug Hilbig, DVM, thinks size may have more to do with it. “When they hit the sale barn, a lot of these cattle are sorted by size,” he says. “Some are probably a lot younger than everything else, so you’re taking the youngest cattle, and they’re not mature enough. We’ll see the same thing in some of the Charolais and any of the big exotics because we’re sorting them up to size. But a five-weight Simmental is a whole lot younger than a five-weight black baldy.”
Some genetics may push the animal to put so much energy into growth and performance that it tends to pull away from other places such as the immune system, says Sturgess.
Hilbig says that chronic rates may follow buyers more than breeds. “There are certain people who like buying discounts. Your late pull comes in before you have a chance to pull it because it’s been sick before arrival. You post these cattle in the first week they’ve been there with 50% lung damage and some have smoldering abscesses. How do you manage your way around it? If you go to the owner and tell him the problem is chronics that he bought, he’s usually making more money per pen on these because he’s buying his profit up front. He’ll take a few of the chronics and getting some value out of them allows him to hold things together.”