Why Didn’t My Vaccine Work this Year?

Brady Campbell, Program Coordinator, OSU Sheep Team

(Image Source: NADIS)

I’m sure that many of you are familiar with the old adage of “if it’s not broke, don’t fix it.” In general, this piece of advice can be misleading as change is needed and certainly essential when trying to improve the efficiency of your operation. However, when it comes to vaccination programs on your farm, this piece of advice fits perfectly. Vaccines are administered as a means to control an underlying issue within your flock or herd. It is recommended to not vaccinate for a specific disease unless you currently or suspect that you will have issues. This is in part due to the nature of the vaccines. Vaccines contain the organism in which create disease. This organism is modified so that the host is able to mount an effective immune response without becoming ill from the disease. As a result, producers willingly give their flock or herd a specific disease; but if your operation does not have issues with it, it is not recommended that you give the vaccine if it is not needed. However, there is one exception is this rule. It is highly recommended that each operation vaccinate with CD&T. The CD&T vaccine is used to protect against Clostridium perfringens types C and D (overeating disease) as well as clostridium tetani (tetanus). For those interested in learning more about this vaccine, check out this Ag-note: Vaccinating with CDT.

Now you maybe thinking, why are we still talking about CD&T? This past spring I have received more questions than ever regarding sick and/or compromised lambs. By sick lambs, I’m not talking about those that have a couch or elevated temperature, I’m talking about those lambs that seem to be acting abnormally. According to the producers, all vaccination protocols that are commonly followed on-farm where adhered to. So, what went wrong this year?

Before we get into the details of vaccination protocols, we need to understand what was happening on-farm. Of the producers that I talked with, they described a set of lambs that demonstrated clinical signs of the inability to use a set of joints, rear legs, and overall stiffness of the body. For those that have experienced these issues, you know exactly what I’m talking about – tetanus. When talking with the producers, they explained that they had followed protocol and administered two rounds of CD&T per label requirements. These lambs were not demonstrating signs of lockjaw and were able to function regularly with the exception of stiff joints and legs. However, the stiffness of joints and legs is a classic sign of tetanus. So, why was the vaccine that was previously given ineffective?

To address this, we need to dig a bit deeper and determine when this vaccine was administered. According to the manufacturers label, the CD&T vaccine must be given at least twice to an individual, as the second round serves as a booster vaccine to build titre levels. Boosters can be given 4-8 weeks apart from the initial dose. However, the label does not state when the first vaccine should be given. In addition, it is recommended that this CD&T vaccine be given once annually. Therefore, getting two birds with one stone, producers can vaccination their ewes and does approximately 30 days prior to lambing and kidding. In doing so, this will allow for the antibodies to be present in the colostrum, thus serving as the newborns first vaccine. However, what happens if you don’t give this vaccine to the females?

It is recommended that this vaccine be given prior to processing of lambs and kids (i.e. castration, tail docking, dis-budding). As these are considered painful procedures, they should be performed as early as possible. Lamb and kid processing most commonly occurs within the first 96 hours of life as this is when all animals are removed from the jugs. Therefore, it makes sense that since you are already handling the lambs and kids that you should be giving them their vaccine, especially if you are creating an open wound. However, this attempt will directly result in a failed attempt to mount any type of immune response as young lambs and kids still have a naive immune system. According to Dr. Bret Taylor, a project conducted at the USDA Agricultural Research Station in Dubois, Idaho outlined that vaccines should not be administered to lambs until they are 14-17 days of age. Vaccines given prior to this age resulted in non-delectable levels of an immune response, thus indicating that the vaccine was ineffective. Therefore, if one of the vaccines that you give occurred in the first two weeks of life and the booster was given around 4 weeks later, you have only truly given one effective vaccination and thus your lambs or kids will require another booster to be fully covered.  If you are interested in understanding more behind the science of this vaccination strategy, I highly encourage you to check out Dr. Taylor’s presentation by either viewing the slides or watching the recording.

For those that commonly give their vaccines at birth, you may want to reconsider implementing a different strategy as this vaccination protocol is not considered an effective treatment. This is not to say that the vaccine itself is not effective, because it is, but only when given at the appropriate day of age in which the body is able to develop an appropriate immune response. Although your management practices have worked previously, the weather patterns continue to change. I believe that as our lambing and kidding seasons continue to become warmer, we will continue to see more issues than ever before. Therefore, it is essential to understand what your flock or herd needs to vaccinated for and when the vaccine should be administered to ensure the greatest level of protection.