“Tipping Point” Concept of Pig Disease
There is a saying, “when a butterfly flaps its wings in one place, a tsunami may occur in another place.” This is obviously an exaggeration, but the point is that small things can have great effects. This is the essence of the “tipping point.” The concept of tipping points has major impact on understanding swine health and production.
Although its principles are clear, a disease-control program including biosecurity doesn’t always work for all farms. No single “recipe-style” program will always work under all situations in any pig farm. Each farm is on its own “unique” situation that sets it apart from other farms. A disease may strike separate herds but the approach to its control differs from farm to farm.
This is because the combinations of risk factors leading to “explosion” of disease are not the same for all farms. When a disease breaks out in a herd, it indicates that risk factors have crossed the “tipping point” for that disease.
Risk factors accumulate slowly to cause disease
It is a common observation that pigs that seemed healthiest are the ones that suddenly get sick and die. This happens especially to pigs with pleuropneumonia (App), despite diligent medication to prevent the disease. Infections such as App may seem acute but the risk factors resulting in a clinical disease had been accumulating for a long time.
Risk factors are varied; some mild, others severe. These factors add upon one another until they cross the tipping point and cause illness in pigs. The big problem is we do not know exactly what risk factors, or how much of those risk factors, contributes to the occurrence of disease. Sudden disease outbreaks are often the result of a slow build-up of risk factors producing no deleterious effects during the time the risk factors are accumulating. Because these risk factors add slowly one upon another without clinical signs, producers, and even some veterinarians assume that they are not important.
Veterinarians, including myself, have been frustrated in demonstrating the importance of disease risk factors to producers. Because of their complex nature, we are unable to demonstrate consistently the negative effects of individual risk factors. This makes it difficult for us to communicate effective preventive medicine practices to our clients, without hazarding the possibility of their losing confidence in us.
The balance beam concept of disease occurrence
The contribution of risk factors of swine disease may be likened to weighing chemicals on a balance beam scale. Suppose you are to weigh some powder chemical on a balance beam scale. After placing a standard weight on one end of the scale, you add the desired chemical to the other side of the balance. As you add more powder in small increments, the balance beam may suddenly without warning slam down. When this happens, you carefully remove about half of the most recent amount placed on the scale but the balance stays down. When you remove some more, the balance still doesn’t budge. You continue removing small amounts of the powder; still no effect. Then after one last tiniest deletion, the balance flew up to the top with a bang. You repeat the process a number of times. After several attempts, the balance arm jumps up and down after only a minor addition to or deletion from the balance pan. The point here is that minor changes at one end of a balance cause dramatic movements in the scale up or down.
The health of a pig herd acts similarly to the balance beam scale. The myriad risk factors for disease, although additive, do not behave in a linear manner. This delicate nature of tipping points is the same reason why the treatment and prevention of swine diseases on farms can be so frustrating. It would have been easier for the veterinarian and the producer if each risk factor moved the herd health scale a noticeable amount toward the balance point. Then, it would have been possible to see how each addition or subtraction affected the outcome. Instead, we have to estimate how much to add or subtract to reach the desired endpoint.
The additions and subtractions of risk factors can occur without any noticeable movement in the scale, and when the scale finally approaches the tipping point, the minutest amounts of risk factors produce dramatic effects. Risk factors accumulate on farms without producing obvious clinical signs until suddenly and without warning an outbreak of disease occurs. When the tipping point is crossed, the scale comes crashing down!
An example: post-weaning diarrhea
The risk factors for disease may be present but cannot be easily pinpointed. Let me present a scenario so we can appreciate better the significance of the tipping point concept of pig disease.
Severe post-weaning diarrhea in 3 to 4-week old pigs in a farm “suddenly” appeared two weeks after a new shipment of gilts, one week after a new shipment of feed, and three weeks after the vet’s last visit. Since nothing else has been changed, the owner suspects that one of these factors must have caused the problem. However, certain factors seemingly far removed from the immediate situation actually may have contributed to the problem. For example, this producer stopped power-washing nursery pens one year ago, and now only removes the worst accumulations with a garden hose. This he did against his vet’s advice on the importance of thorough cleaning using high pressure. For the last 12 months, minus the power washing, the pigs have been growing fine — a proof to him that the vet has been wrong about the value of power washing. In this situation, further emphasis on sanitation only frustrates the vet, and annoys the farm owner.
For the past eight months the vet has repeatedly brought to the owner’s attention that the feeders should be adjusted to avoid wastage and discourage overeating by the pigs. The owner countered that the pigs don’t waste much feed and they aren’t getting sick anyway, and if he tightens the adjustments, the feeders plug up. For five months the veterinarian has gently reminded him that newly weaned pigs are piling up in the nursery because of low ambient temperature. But the owner reports that the pigs are doing fine in their cool pens, and at the same time he saves on fuel for heating.
Later, almost without warning, post-weaning colibacillosis explodes in the nursery. Still the owner insists that the risk factors, which the vet believes are responsible for the outbreak, are not important on his farm. Instead, he wants to put the blame on somebody for bringing this new bug on his farm. He asks the vet to give a quick antibiotic treatment while he searches for the source of the E. coli.
The vet starts in-water medication that stops the diarrhea. The owner fails to pin the blame on any one party for bringing this new bug on his farm. Meanwhile, as the medication cost rises, the owner wants an alternative to water medication, perhaps with less expensive antibiotics.
The vet insists on power washing, heat, and feeder adjustment. The owner says he’ll try power washing, but in his mind he knows it won’t help. He power washes the nursery prior to pig entry, stops the medication, and calls the vet the following week only to report the pigs are still scouring. Convinced that power washing is time-consuming and not helping solve the scouring, he goes back to the garden hose but this time turns up the heat in the next nursery room he fills with new pigs. This batch of pigs also scours. So he turns down the heat to save on heating bill, and decides to give feeder adjustment a try. This seems to work but only for one batch. The subsequent batches of pigs scour despite the feeder adjustment. By this time, he seems to read the word “idiot” on the vet’s forehead each time the vet walks into the farm.
Keeping away from the tipping point
Disease is a discreet variable, i.e. disease occurs or does not occur. We see, risk factors all increase the likelihood of disease. The severity of disease however does not increase with each addition of a risk factor. Only when a critical number of risk factors are in place does pig health tip to the disease state. For example, a well-designed and well-managed nursery is unlikely to break with severe colibacillosis, even if some pens are occasionally not washed, or a feeder adjustment is overlooked, or a thermostat fails. However, the fact that these isolated deviations from good production practices do not produce disease outbreaks is not evidence that these risk factors can be ignored in a disease prevention program. Just like the balance beam scale, disease comes crashing down when you least expect it after a critical number of risk factors accumulate on a farm.
Observing, without “cheating”, sound standard operating procedures based on science and farm experience ensures that farms keep the balance strongly in favor of pig health and ensures that the pigs will not easily tip towards a disease outbreak. Your veterinarian is still the best source of advice on herd health management.
By Elito Ferry Landicho, DVM