A Practical Approach to Vaccination Protocols

 

Vaccination programs are a major component of the control and prevention of BDV infections. Given the economical losses associated with BVD it is no wonder vaccination protocols are one of the most frequently asked questions of veterinarians. It is important to communicate with producers and design a vaccine program that best compliments individual operations. Customization of vaccine protocols should take into account the following aspects:

Vaccine Types:

When an animal is exposed to a disease challenge, such as BVD there are essentially two possible outcomes. The first being that the animal gains immunity from the exposure without identifiable illness of the disease, and the second being the animal will become sick due to the challenge, recover if possible and be immune to later exposure. The goal of a vaccine protocol is to prevent disease. This is achieved though exposure to the disease causing pathogen without actually causing the disease. Vaccines act to enhance an animal’s immunity before an animal is exposed to a natural challenge of the disease. There are two types of vaccines available in Canada, they are Modified Live Vaccines (MLV) or killed vaccines. MLV are attenuated strains of the virus that are altered in a way to prevent active disease within the animal, while allowing the organism to multiply and trigger an immune response. While MLV’s stimulate both humoral and cell mediated immunity, cellular immunity is the strongest response. MLV tend to produce a higher protection and longer lasting immunity towards a BVD challenge, however there are some reports of postvaccination mucosal disease, immunosuppression and fetal infection resulting in abortion or congenital anomalies following vaccination with MLV products. Killed vaccines contain pathogen that is completely inactivated and cannot replicate within the animal. This type of vaccine stimulates a greater humoral immunity than cell mediated. Killed vaccines are thought to have a larger safety margin than MLV. However killed vaccines require an initial vaccine followed by a booster two to four weeks later to stimulate a primary immune response, resulting in increased handling of the herd. In addition the duration of immunity established by killed vaccines is though to be shorter than that of MLV. Currently in Canada, there are over 40 licensed vaccines available to vaccinate against BDV. Many of these vaccines are multivalent, protecting against other disease challenges such as IBR, PI3, BRVD and RSV at the same time.

 

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Immunity:

When considering immunity there are two types: Passive Immunity and Active Immunity.

Passive immunity involves the absorption of antibodies from an external source, with the most important passive immunity transfer being maternal antibodies from the dam’s colostrum to the offspring within the first few hours of life. The maternal antibodies are absorbed through the intestinal wall and provide the main mechanism of immunity for the first few months of life, while the calf’s own active immunity starts to develop. The ability to absorb colostrum antibodies rapidly wanes after the first 9 hours following birth, making it essential that an animal receive colostrum before gut closure is complete. 

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“Colostrum is every calf’s first and most important vaccination” W. Walker, DVM.

Active immunity can be further subdivided into cell mediated immunity and humoral (antibody) immunity.  During cell mediated immunity macrophages, monocytes, T-helper cells, natural killer cells and T-lymphocytes are activated in response to the recognition of foreign antigens. Humoral immunity involves macrophages, plasma cells and B-lymphocytes in the production of antibodies against foreign antigens on the outside of cells. In general viral antigens involve cell immunity to a greater extent than humoral immunity since the virus actively replicates within the cell.

Memory is an important component of immunity. When an animal is challenged by a pathogen the immune system recognizes the pathogen and stimulates the immune system defences to prevent the establishment of disease. Annual booster vaccines are critical to maintain memory and efficient response of the immune system to a challenge.

It is important to recognize vaccine programs are not a replacement for good herd management practices.  In addition to vaccination, control programs should include identification and removal of PI animals as well as biosecurity measures such as isolation of new breeding stock.

Generic Modified Live Vaccine Protocol:

Products: Bovishield, Express and Pyramid vaccines

*With the help of a veterinarian, every producer should develop a vaccination program to meet the needs of the individual operation*

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Generic Killed Vaccine Program:

Products: Cattlemaster, Sentry and Triangle vaccines

*With the help of a veterinarian, every producer should develop a vaccination program to meet the needs of the individual operation*

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