Producers expect a lot from vaccines, and most of the time they are happy with the results. Occasionally, however, they experience what they perceive to be a “wreck”. Every producer has their own definition of what constitutes a “wreck." Some think they’ve had a vaccine failure if they had to treat a single animal. Fortunately, most have realistic expectations about vaccine performance. As veterinarians, it should be part of our job to help producers understand that vaccines are only one of the tools we use to help control disease, and that their success depends on good management.
Whether or not disease occurs is basically a function of two things: degree of challenge and level of resistance. Challenge is increased by commingling cattle, and for most calves that is certain to occur. Vaccination is the tool by which we hope to increase the level of resistance to specific known pathogens. If we can reduce the degree of challenge and increase the level of resistance, there is a much greater chance that the result will be healthy calves. Unfortunately, there are numerous factors that cause resistance to go down and challenge to go up, which leads to sick calves. The most “perfect” vaccination program can be broken by stressful management or environmental factors that reduce the animal’s resistance level and allow disease causing pathogens to proliferate.
When disease occurs in vaccinated animals, one of three different things is usually to blame: “broken” management, “broken” animals, or “broken” vaccine. Sometimes a combination of all these are involved. The challenge is to investigate and determine where the blame should really lie so that steps can be taken to reduce the chance of similar problems in the future.
“Broken” animals are the result of a variety of stressors, including nutritional and environmental, that lead to a decreased level of immune function. Stress induced cortisol release has a negative effect on the activity and function of most of the white blood cells involved in the immune response, leaving the animal susceptible to infection by microbes, even if it had been previously vaccinated for some of these pathogens.
“Broken” management is frequently the underlying reason for sick animals in the face of adequate vaccination. Many management procedures contribute to stress and are additive in their effect on the animal. When management decides to wean, castrate, dehorn, vaccinate, commingle, ship, etc., at 4 p.m. on a summer afternoon when the temperature is 95°F, it is not surprising that the calves “don’t look so good” the next day. And, the negative effect on the immune system from this experience may linger for a number of days.
While “broken” vaccines are always possible (less than optimal efficacy, heterologous field strains, etc.), more often management (including poor vaccine handling), nutrition, and environmental conditions are to blame by creating a situation in which stressed calves are not immune competent enough to respond to vaccination. Because it is always easier and less painful to point the finger elsewhere, and producers don’t always investigate the cause of a problem thoroughly, vaccines tend to be the “whipping boy” of animal health wrecks.
Vaccination is the physical process of getting the vaccine into the animal and immunization is what the animal’s immune system does with the vaccine after it is injected. As previously mentioned, stressed animals may have less than optimal immune function, resulting in marginal response to vaccination and subsequent lack of adequate protection when challenged.
Although vaccines are rarely 100% effective at stimulating protection even in optimal circumstances, it is not likely that the vaccine is “broken” when a serial of 250,000 doses are manufactured, and only a couple of operations have problems. It is important to check with the technical services veterinarians for the vaccine marketer to get some idea of the incidence of complaint calls and for assistance working up the case before jumping to the conclusion that the vaccine is no good. Spend a little time helping producers understand how to properly store and handle vaccine and educate them on what they should be doing to help improve the chances of getting their calves properly immunized.
Finally, it is important to have realistic expectations as to what a vaccine can or cannot do. Sometimes calves will still need to be pulled and treated and if it is not done in a timely manner, death loss may occur. When this happens, one finger might be pointed at the vaccine, but three other fingers are pointing back at the animal caretaker.
This tip contributed by Roger Winter, DVM, AgriLabs.