by Steve Wagner
Dr. Ernest Hovingh describes himself as ‘a James Herriot kind of man.’ Herriot was a veterinarian in the UK’s Yorkshire Dales who wrote a series of bestselling books about his practice nearly 40 years ago. Dairy cows are where Hovingh has spent the past 20 years of his life. “But,” he explains, “I also work on the bio-security aspect of things.” Hovingh honed in on infectious disease for his presentation at Penn-Ag’s Pork Expo and Poultry Progress Day at Shady Maple in East Earl, PA.
When you have a susceptible animal in the flock, Hovingh says, you have to figure out how disease gets from one animal to the other. Outreach through the air is one way. Airborne transmission can happen on a small scale where one animal is standing a few feet from the other. “It can also happen on a larger scale,” he says, “where we can look at transmissions between different facilities.”
What’s known as direct contact has to happen within the immediate environment. Exposure can also be achieved through feed, vectors or fomites, which are inanimate objects like disposal boots that could transfer an organism to a potentially susceptible animal; it is not a living organism.
“In some animals we can detect the immune response early on,” Hovingh says. “In others, we might not be able to detect it visibly at all. Extra testing might show what animals are infected. Now, some animals may get infected and simply recover, which might happen without you even being aware of it. The more likely scenario is that you’re going to have animals that develop some kind of disease, whether it’s a mild clinical disease or a severe one. We have to remember that there is also sub-clinical disease where animals can be infected, actually have a disease, and you can’t see that visibly at all.”
Merely having an organism, a virus, or bacteria, does not necessarily mean that the animal is going to get the disease. If a whole flock or herd is exposed to a specific bacteria, it doesn’t mean that every single animal in that group is going to get sick. Pathogens aside, there are other factors to determine whether or not animals will become ill. Pathogens are certainly important. But there are environmental factors that are equally important as well as factors about the host.
Environmental factors might include stocking density. If too many animals are put into one location, more than is ideal, you might end up with a higher exposure simply because there are more animals together. Secondary problems could creep in with humidity and temperatures getting too high or too low. Ventilation could be on the weak side and not allow air to turn over in the allotted space. Animal mixing, combining age classes, can raise the ante, much like schoolchildren in late August or early September can be a terrarium for colds and other illnesses that were absent all summer.
A host’s age can play a major part in disease onset. Often very young animals tend to be very susceptible to infection. Immune status of the animals can be important, as well as production status. Genetics, too, can play a role in whether an animal is susceptible to disease. “We talk about positive transfer of immunity,” says Hovingh, explaining the chain of potential prevention, “but more important, we speak a lot of activity immunity. We’re actually vaccinating animals to try and decrease the chance they are going to be infected, and if they do become infected, decrease the chance that they will become diseased.”
It helps to know the difference between vaccination and immunization. “Lots of people say ‘I vaccinate my animals,’” according to Hovingh, “but what you really want to do is immunize them. You can spend a lot of money vaccinating without really getting an effective immune response. You need to make sure that what you are giving your animals as part of your bio-security program is truly developing an immunity that will be helpful in preventing disease.”
Hovingh also suggests looking at the disinfectants that you use. Are they generally good for the different classes of bacteria or viruses that are causing concern? It doesn’t do a lot to just throw disinfectant at a pile of manure. “Cleaning something before disinfecting it,” Hovingh cautions, “will make that disinfectant more effective.”
So, what is your actual protocol? Are you cleaning your boots? Are you cleaning your equipment prior to disinfecting? “Knowing that,” he says, “will be much more useful than just saying ‘yes, I use the latest and greatest disinfectant.’”
Overall, one of the things you can do is to keep the pathogen out of the farm. If you can successfully do that, then disease should not be present, theoretically. The reality is that animals will still be susceptible if that pathogen shows up. This brings us to the concept of the closed herd, one that does not bring in outside genetics, or one that is free of disease. Or even one that is prevented from mating. “If you have sick animals, adult bovines, it isn’t a good idea to house them next to the calves,” reasons Hovingh. “Here you have dairy animals that are likely shedding the highest number of bacteria or viruses, and putting them right next to the animals that are most susceptible.”
He recapped by stressing the minimizing of pathogen load, making the animal environment as healthy as possible, and making sure that animals have the highest resistance possible against disease.
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