With societal and political pressure surrounding antibiotic use in food animals, preventing disease outbreaks is increasingly important. The words “immunization, not just vaccination” may sound familiar in the context of discussing vaccines, but what is really meant? What is the goal of vaccination, and how can that outcome be achieved? Multiple factors influence an immune response and how it performs when faced with a natural infection. These include vaccine handling, timing of vaccine administration, and the health and nutritional status of the animals. The objective is to give the defense system the edge against a challenge by implementing proper management practices.
The immune system is a complex organization of chemical mediators, cells, tissues and organs that work in collaboration to address potential invading pathogens. Some components are utilized immediately, while others require time to develop. Memory is formed in the latter phase, and antibodies have a major role here. Immunity is developed through a cascade of events that are dependent on multiple interconnected elements. The mechanisms that result in protection are active processes dependent on energy and other proper nutrients. While it may seem the job is done once a vaccine is administered through a syringe, there are far more intricacies that must align for a successful response.
Details matter with vaccine handling
A good place to start is with thinking about the vaccine itself. Product storage, cleanliness of administration and Beef Quality Assurance (BQA) principles are receiving extra attention, and rightfully so. Precautions, warnings and directions on the label are important. Since some vaccines come “ready to use” while others require mixing, it is critical to adhere to the appropriate guidelines relative to discard. Statements regarding the number of needle punctures in the rubber stopper and the time frame over which to use the entire contents of the bottle are meant to reduce the risk of contamination.
Attention is often given to ensuring vaccines do not become too warm prior to use, yet the opposite extreme is counterproductive as well. Freezing certain types of vaccines is extremely problematic. There is reason to worry about the disruption ice crystals may cause to the immune-stimulating portions, called antigens, and the substances released as a result. Just as great a concern is the damage to the adjuvant, which is a critical mixture of ingredients added to the product to help ensure safety and efficacy. When these fractions have been affected by cold temperatures, it is unlikely the vaccine will behave as intended, and the animals receiving it could experience severe adverse reactions.
There are careful considerations to weigh when choosing a syringe type with tradeoffs between multidose and single-use options. The pistol grip syringes are convenient for reducing fills when working with a group of cattle, but a good amount of effort is necessary to maintain them in clean condition. Bottle-mount syringes seem like a logical choice when the number of cattle to work is large. However, the drawbacks are similar to pistol grip syringes, with an additional concern because the gauge of the needle that draws the product into the chamber is quite large. The hole that is created following use is unlikely to seal well for reuse if there are doses remaining. With single-use syringes being sterile when first opened and easily discarded afterward, there is an advantage over the other options. The shortcoming, though, is the impracticality of repeated injections for many animals and the compromise to the integrity of the bottle top associated with entering it many times. With the loss of sterility, abscessation at the injection site may result. Allergic reactions and death are also possible.
Timing is critical
Vaccines need to be given early enough to include the proper number of doses, spaced the appropriate distance apart prior to disease exposure. Many products recommend an initial two-dose series when animals have not been given it before. This information is provided by the manufacturer, and a range is usually indicated for the second dose. Two to four weeks later is commonly listed. Newer research on principles of immunology suggests aiming for the latter part of that interval. After the booster dose, there is yet another lag for antibodies to appear. Generally, it takes 10 days to two weeks for this to happen. The remaining consideration is the incubation period of disease prior to clinical signs. Pathogens are often harbored for a few days to a week ahead of any indication of illness. When all of this is summed together, it might be necessary to start a vaccination protocol four to seven weeks prior to a known risk period for a disease to have elicited protection in place before a challenge.
Animal factors should not be underestimated
The goal of vaccination is to create a sufficiently high enough level of immunity in an adequate proportion of an animal population to prevent or at least reduce the likelihood of significant illness. If there are circumstances negatively impacting individual cattle, immune function can be hindered, and it becomes increasingly unlikely that herd-level immunity can be achieved. Young age, previous or current infections, stressors and suboptimal nutrition can be reasons why the intended outcome might not happen.
Calves are born equipped with a working immune system; however, the machinery is immature and may not respond with the same vigor that occurs when they are older. Furthermore, these young animals have more limited nutrient reserves (energy, vitamins, minerals, etc.). Alongside elevated requirements for body maintenance and growth, the metabolic demands of immune activity may quickly deplete stores if not supported appropriately.
Disease either in the past or present adversely impacts vaccine immunity. It might seem like immunity developed through natural exposure is a good thing, and it can be, if the challenge is mild enough to not overwhelm normal function in other organ systems such as the lungs, for example. The dependence on finite internal resources for fuel to drive this process means concurrent demands can limit the desired response to vaccination.
One specific infection, bovine viral diarrhea virus, is particularly worrisome because it can cause immunosuppression. A persistently infected calf in the herd can wreak havoc by constantly shedding infectious particles to herdmates and contributing to the downregulation of the immune system in increasing numbers of animals.
Stressors such as extreme heat or cold, weaning, commingling, changes in accessibility to food and water, diet alterations and transportation can have a dampening effect in much the same way as with an existing infection. The hormones released during these events reduce immune function. As highlighted already, nutrition has an important role. Energy in the form of glucose sugar, plus vitamins and minerals, is vital for the development of immunity. The transition stages of cattle are accompanied by fluctuations in the availability or levels of various nutrients. Nutrients become restricted when partitioned to power bodily needs. A shortage or a need by other life processes occurring simultaneously creates an impediment for the immune system.
By recognizing the pitfalls, it is possible to adjust and adapt procedures to create a more supportive environment for vaccination to generate immunity. Not all circumstances with a potential negative impact are avoidable, but the key is to limit as much as possible having multiple conditions collide or overlap at the same time. There are ways to work through and overcome situations by tailoring a vaccine program to a specific setting on a farm. A veterinarian and nutritionist are invaluable resources capable of identifying opportunities and guiding necessary modifications. Refining the ways in which cattle and vaccines are managed together will enhance the function of the natural defenses, build robust immunity and improve disease prevention for healthier, more productive livestock.
