Bovine respiratory disease (BRD), or pneumonia, is the most common cause of death in cattle over 4 months old. Many different commercial vaccines are available for protection against organisms that cause BRD, but sometimes cattle get BRD even when they are vaccinated. This article will review some of the more common causes of perceived, or real, BRD vaccine failure or lack of efficacy.
Setting expectations
Firstly, we need to understand what a BRD vaccine failure is and what it is not. In the realm of herd production medicine, is the BRD-associated illness or death of one or two calves a failure? It can seem like it is if you only have a few calves. In a production system that backgrounds or feeds hundreds or thousands of calves, a single dead calf or a few death losses in a group might be considered a tremendous success. In some production systems with ultra-high-risk calves, a 30% to 40% morbidity or sickness rate and a 10% to 15% or more death loss can be acceptable. For other production systems that purchase lower-risk, vaccinated or backgrounded calves, a less than 5% to 10% sickness and 2% to 3% death loss may be the target. The point is that the amount of tolerable sickness and death loss depends on the type of cattle purchased, the producer’s risk tolerance and the management system.
Also, consider the response to treatment. Calves vaccinated against BRD will respond better to treatment than unvaccinated calves. If a group of vaccinated calves get BRD but recover with fewer treatments, lower mortality, with less labor and drug expense than unvaccinated calves, is that considered a vaccine failure?
The calves have pneumonia but I vaccinated them
Cattle respiratory vaccines can be perceived to fail for several reasons. Usually, the causes fall into one of three general categories: failure of the animal, failure of the vaccine or failure of people and management.
Failure of the animal
The term non-responsiveness or primary vaccination failure is the inability of the normal healthy animal to mount sufficient protective antibody responses after the primary or booster vaccination. This phenomenon affects about 2% to 10% of vaccinated healthy individuals.
Young cattle may also have a reduced response to vaccination due to the presence and interference of maternal or colostral antibodies on the response to vaccination. Generally, calves under 3 months old are still under the protection and influence of the colostral antibodies received at birth. Historically, veterinarians were taught and instructed producers to not vaccinate calves less than 3 months old due to maternal antibody interference. More recent data have shown that this is not the case with the use of modified-live vaccines (MLV). Vaccination at a young age can be beneficial. It is frustrating when the largest, nicest calves are the ones getting ill from BRD. Many times, these are the oldest calves whose maternal antibodies and protection have waned more than in the younger calves.
First-calf heifers tend to have lower volume and quality of colostrum than more mature cows. Heifers also lack the mothering experience compared to the older cows in the herd. Calves born to heifers tend to have lower maternal antibody levels and be at higher risk for BRD than calves from mature cows. It is common to see BRD outbreaks impact the calves of heifers more than the calves of mature cows.
Failure of the vaccine to stimulate immunity
The quality of the vaccine itself is crucial. Vaccines that are not properly manufactured or have issues with the antigen used may not provide the desired immune response. Fortunately, all commercial and autogenous vaccines are manufactured under a USDA license intended to ensure vaccine quality.
Using a vaccine that does not match the target organism (antigen) or the specific strains of pathogens present in the herd can lead to inadequate protection. Antigen problems do occur more frequently than many people realize. Complete BRD protection against all possible pathogens is not available in a single product or injection. Don’t expect protection against an organism that was not included in the vaccine used. Organism strain variation is also a major concern when vaccine lack of efficacy is suspected. The article, “The importance of strain variation in vaccines” authored by Randy Shirbroun in the May 2024 issue of Progressive Cattle provides an excellent overview of how the strain variation of an organism may negatively impact the efficacy of cattle respiratory vaccines.
Vaccines can contain either MLV or inactivated killed organisms. MLVs contain organisms that have been modified by the manufacturer to not cause clinical disease, but the organisms are still able to replicate in the animal and stimulate immunity after vaccination. MLV respiratory vaccines in many cases are believed to be more efficacious than their killed vaccine counterparts.
Failure of people and management
Often, management failures are the primary reason cattle BRD vaccines are perceived to fail. Vaccinating calves too early in life, when maternal antibodies are still present, can interfere with the vaccine’s ability to stimulate a protective immune response. Also, vaccinating too late or too close to the risk of getting BRD is not recommended. Some vaccines may claim protection in a few days after administration, but a complete response often takes a few weeks to achieve. Vaccinating on the truck or at the sale barn may be convenient, but it is not optimal for a protective immune response.
Vaccines need to be stored at specific temperatures. If the vaccines are not kept within the recommended temperature range, their effectiveness can be compromised. Administering the vaccine incorrectly, such as using the wrong injection site or technique, can reduce vaccine efficacy. MLVs must replicate in the animal to stimulate an immune response and ensure maximal efficacy. If MLVs are mishandled either by improper storage such as becoming too hot or freezing before administration, the organisms may perish and not replicate after administration, and a reduced or incomplete immune response can occur. Vaccines are available as single-dose “no booster” products and as traditional two-dose products that require a primary and booster vaccination. Single-dose products are generally developed for producer convenience over vaccine efficacy. Failure to properly administer a booster injection can be a major reason for vaccine failures. Vaccine selection and product handling are critical in optimizing BRD protection.
Cattle nutrition plays a crucial role in the effectiveness of vaccines. Proper nutrition ensures that the immune system has the necessary resources to function optimally. Proper nutrition includes providing adequate levels of proteins, vitamins and minerals, which are essential for producing antibodies and other immune responses. Energy deficiencies can lead to poor animal performance and low body condition, which can weaken the immune response to vaccines. Deficiencies in trace minerals like zinc, selenium and copper can impair immune function. These minerals are vital for various immune processes, including the production of white blood cells and antibodies. Adequate protein is necessary for the synthesis of immune cells and antibodies. Protein deficiencies can lead to a weakened immune response, reducing the effectiveness of vaccines. Good nutrition helps maintain overall health, reducing stress and the likelihood of concurrent infections, which can interfere with the immune response to vaccines. Ensuring cattle receive a balanced diet with all necessary nutrients can significantly enhance the effectiveness of vaccination programs. Sick cattle go off feed, and the normal trace mineral, energy and protein intake can drop quickly due to reduced feed intake and increased immune system requirements.
Stress from weather factors, poor nutrition or existing health issues can weaken the immune system, making it less responsive to vaccines. Stress triggers the release of cortisol, a hormone that can suppress the immune system. This suppression can reduce the body’s ability to respond effectively to vaccines. Stress can lead to lower production of antibodies and white blood cells, which are crucial for the immune response. This means that even if the vaccine is administered correctly, the immune system may not produce enough antibodies or enough white blood cells to provide adequate protection. Stressed cattle are more susceptible to infections, which can interfere with the immune response to vaccines. If an animal is already fighting off an infection, its immune system may not respond as completely to a vaccine.
Stress can cause behavioral changes that might affect how cattle respond to handling and vaccination. For example, stressed animals might be more difficult to handle, leading to improper administration of vaccines. Stress often leads to reduced feed intake, which can result in nutritional deficiencies. Low-stress cattle handling has been promoted to improve cattle welfare and minimize stress of handling. In a low-stress handling study at Iowa State University, it was demonstrated that 18.8% of the conventionally handled calves were treated for respiratory disease compared to 7.4% in the low-stress-handled calves. The conventionally handled calves had a lighter hot carcass weight compared to low-stress calves (728 pounds versus 757 pounds; p = 0.0074). This study provides evidence that handling procedures to minimize stress in newly received calves are associated with health and performance benefits in feedlot cattle.
Conclusion
Effective cattle management, vaccine selection, timing and nutrition are necessary for cattle respiratory vaccines to be effective. When coupled with realistic expectations, vaccination of cattle for BRD can be greatly beneficial and rewarding. Managing stress through proper handling and minimizing environmental stressors can help improve the effectiveness of vaccination programs. Working with a veterinarian familiar with cattle diseases, your management style and the BRD risk factors for your herd is critical for a successful herd health program.
