Spring thaw brings wet and muddy conditions.
After several dry years in north-central Alberta where I practice, this is optimistically looked upon as a sign there will be enough moisture to get the grass started. For producers with young calves, however, it can be a nightmare trying to keep them clean and dry.
With recent wet conditions, we have seen increasing numbers of scouring calves. I’m often asked why calves have scours if the cows and heifers have been vaccinated with a scours vaccine.
Vaccinations are just one way to prevent disease. Whether an animal gets a disease depends on many complex interactions between the animal, the agent causing the problem and the animal’s environment.
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Animal factors that need consideration include its immune status, maternal protection, including quantity, quality and timing of colostrum intake, its age and genetics, any additional infections or problems it may have, and its vaccination and nutritional status.
Environmental factors include temperature, air quality, feed and water quality, density of animals, stressors such as transportation, and infection pressure, which is the amount of bugs in the animal’s life that it has to deal with.
Agents or organisms that cause disease have various abilities to cause disease and may be spread easily. Some may also live for extended periods outside the host.
These are just a partial list of the many factors that cause disease.
Remember that vaccines may fail because of factors such as improper storage, exposure to ultraviolet light or disinfectants, expiration or use of a modified live vaccine too late after mixing with its diluent.
It is important to properly administer vaccines. The correct dosage must be given in the right location using clean needles and syringes. Give a calf its vaccination too early in life and there may be interference with its maternal antibodies. If vaccinated in the middle of a disease outbreak, it may be too late to be of much benefit.
Vaccines can fail to properly protect an animal even when it is properly administered and an immune response has occurred. Vaccines stimulate mucosal, cell-mediated or antibody immunity to various degrees. If the necessary type of immunity has not been stimulated to an adequate level, the vaccine will likely fail.
The agents that cause disease, such as viruses and bacteria, are constantly changing and mutating, which means the vaccine may not adequately protect the animal against the new strain.
Duration of immunity of the various vaccines will also differ, so protection may have waned by the time the animal actually encounters the disease.
With scours vaccinations, I believe many of the apparent vaccine failures are due to a heavy infection pressure by large numbers of organisms. In other words, living in a highly infected environment will often overwhelm the calf’s defence mechanisms.
Daryl Meger is a veterinarian and outdoors enthusiast in a mixed animal practice in Westlock, Alta.
