by: Heather Smith Thomas

Occasionally cattle experience a reaction to a drug (injected, applied topically or given orally). An allergic reaction can be mild and local (such as swelling at the injection site after vaccination) or serious and fatal—if the animal goes into anaphylactic shock.

The drugs we administer are “foreign” to the animal's body, and in the case of vaccines the goal is for the body to recognize it as foreign and develop antibodies to combat these foreign agents (antigens) in the future. The vaccine will therefore enable the animal to create an immune response. On rare occasions, however, the animal may develop an acute allergic reaction to a foreign substance. Reactions can range in severity from hives/itching to systemic shock with fluid in the lungs and sudden death.

Mark Alley, DVM, MBA (Clinical Assistant Professor, NCSU College of Veterinary Medicine) says that vaccine reactions are probably the most common—since cattle are often given vaccinations—and there are two general categories: the reactions that are not life-threatening and the ones that are. “It's hard to predict when a life-threatening reaction might occur. When I typically see these, it's usually due to a combination of events. There are usually multiple vaccines being given to the animal. Any of the gram-negative bacterial vaccines will contain some endotoxins. These include pinkeye, foot rot, leptospirosis, pasteurella, haemophilus, brucella, salmonella, and E. coli,” he says.

“When these vaccines are manufactured, there are still some endotoxins present. Some may contain more than others. So there is more potential for risk if you are giving several of these at the same time. I usually recommend no more than a maximum of three at once (and two is better), especially in animals that may be getting these vaccines for the first time,” he says.

The greatest effect will usually be seen in the lungs if the animal starts to go into shock. “The first sign you might see is rapid respiration and difficulty breathing,” says Alley. These signs may appear within 10 to 20 minutes after an injection. As the reaction gets worse, the lungs fill with fluid and the animal may try to breathe with its mouth open and tongue extended, trying to get more air. The animal may have muscle tremors, then stagger and collapse. There may be bloody foam from the mouth.

“Another common sign of adverse reaction is welts (hives) suddenly developing on the skin. These may vary in size from a dime up to a 50 cent piece or larger. These can appear within minutes after giving an injection, or it might be two or three hours before you notice them. Usually it's rare to see them appear after 24 hours,” he says. The quicker a reaction starts, the more serious it is. If it takes longer than two or three hours for the reaction to occur, there is more chance that the animal will survive and recover without treatment.

“Along with endotoxin in the vaccine, the other risk factor that I commonly see, here in the Southeast, is heat. If it's hot when you are working the cattle, and they have gotten excited when you were getting them in, they are more likely to have reactions to the vaccines. We recommend that whenever you purchase vaccine, you also purchase some epinephrine to have on hand to give an animal, in case of a reaction.”

If it's an acute reaction, the animal needs to be treated immediately; you don't have time to drive to town to get a bottle of epinephrine. “If the animal is still alive by the time you get back, it will probably recover anyway.”

Epinephrine should be given as soon as you notice an animal having a reaction, at proper label dose for the size of the animal. A second dose can be given in 15 to 20 minutes if necessary.

Some people use antihistamine, but it's not as effective as epinephrine. “If someone calls me and they don't have any epinephrine, antihistamine might be better than nothing. The other option, as long as the animal is not pregnant, is to give an injection of steroid such as dexamethasone. Giving epinephrine and dexamethosone together can often reverse the shock and save the animal,” says Alley. If the animal is in serious shock, you may decide to give the steroid even if she's pregnant, because it's more important to save the cow than to worry about possible abortion from the steroid.

Sometimes other injectable products (not just vaccines) will cause an animal to have a serious reaction. Some individuals react adversely to penicillin, especially if it is injected into a vein rather than into the muscle.

“Anything that you give an animal has the potential of causing a reaction, or giving it in an inappropriate way. If it is labeled to be given IM or Sub Q and you accidentally give it IV, for instance, this can create serious reactions. Hopefully, if everyone is following BQA (Beef Quality Assurance) guidelines when giving injections, these sorts of things won't happen as often,” says Alley.

But sometimes there is nothing you can do to prevent a reaction. Some individuals are just more sensitive than others to certain drugs. Often it is the second or third exposure that causes a serious reaction.

“The more times they are exposed to it, the more likely for a serious reaction to occur because the body has already been sensitized to that particular antigen,” he says. You might not be expecting a reaction in an animal that has already received this type of vaccine in the past.

It's always a good idea to monitor the animals for at least a couple hours after giving them an injection or a pour-on medication, or even an oral medication. Stockmen don't always think about the possibility of reactions resulting from the things we routinely give the animals.

“If possible, I always like to have the animals where we can at least walk back through them or get close to them afterward, to see how they are doing. Most of the clinical signs will occur within 2 hours or less if the animals are having a serious reaction. There are some cases that may be longer, but the later the signs occur, the more likely the animal will recover on its own,” he says.

“The good thing about it is that severe reactions are uncommon (only about one in every 10,000 cattle exposed to a foreign substance). But it is quite memorable when it happens, and it may take immediate treatment to save the animal.” It's always good to be prepared, with some epinephrine on hand, and know how to give it. The good thing about epinephrine is that if we can just get it into the animal—regardless of whether we inject it IV or SubQ—it will save the animal. But you should talk to your veterinarian ahead of time and be able to give the proper dose, based on the concentration of that particular product.” An overdose can be dangerous, as well—making the animal's heart beat too fast.

It's also wise to buy new bottles of epinephrine from time to time, so that you have some on hand that's not too old and out of date. “Technically you shouldn't use it if it's too old, but if that's all you have on hand it would probably help. But after you use it you'd need to talk with your veterinarian or the company that manufactured it, to figure out an appropriate withdrawal time. We would assume these drugs would become less effective as they get old, but that's part of the problem; we don't know if they become less effective or more potent,” he explains.

Some of the organophosphate pesticides are notorious for adverse reactions, especially when overdosed. This was true of the old systemic products for lice and grubs (such as Warbex), but can also happen with some of the insecticide ear tags. “We've seen young calves that had come through a sale barn and were highly stressed, and were doing poorly, and we finally figured out that they were reacting to their insecticide ear tags.”

If you notice any adverse events after vaccinating or administering any kind of drug or product, you should contact the manufacturer. “That way they can keep tabs on what's happening with their product. There may be something that is going on with a certain serial group or lot number, and they can identify this and maybe minimize risks for other producers,” he says. This would be especially important if you have more than one animal that reacts to a certain product.     

There are a lot more reactions that occur which are not life-threatening—the lumps and bumps at an injection site, for instance. A neck injection may create so much swelling that the animal has trouble walking for a few days; moving the shoulder forward may be painful with that big sore neck lump just ahead of the shoulder. “Those are more common, but if it happens to several animals in the group you should probably talk to your veterinarian about it, and contact the company that made the product. They keep a tally on those, to ensure that the products are safe,” says Alley.

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