In the future, calves may not need booster shots: they’ll be able to eat their vaccines with breakfast. Researchers led by Dr. Philip Griebel from the Veterinary Infectous Disease Organization in Saskatchewan are developing an orally-administered vaccine for calves.

Animals, producers, and consumers would all benefit from oral vaccines. Compared to traditional injections, they would be cheaper and easier to administer, not to mention less stressful for the animals. Oral vaccines would also eliminate food safety risks associated with the foreign material that gets deposited at injection sites.

The researchers are optimistic that oral vaccines will even out-perform injected ones at warding off infections of mucosal surfaces in the intestines and lungs.

If the vaccine proves effective, it will be used to immunize calves during the neonatal period when they are most susceptible to disease. This period is critical. Of all calves who die younger than one year old, 75% die in the first 28 days of life.

The researchers, now about half way through the project, have had considerable success so far. Their first task was to produce alginate microspheres, the part of the vaccine that will carry the active component across the animal’s gut lining. The microspheres are less than 10F m in size, tiny enough to pass into the immune system through Peyer’s patches, specialized lymphoid tissue in the gut.

The next tasks in the project were to incorporate bovine adenovirus vaccine vector into the microspheres, and then to see if the vaccine would induce an immune response when injected into animals.

The researchers had variable success at combining the bovine adenovirus vaccine with the alginate microspheres. In one trial, 80% of the vaccine vector was absorbed, in a second only 40%. Future work will have to be done to improve the efficiency of this step.

Once the vaccine was completed, the researchers performed an experiment to determine whether the active component would be released by the microspheres in an animal’s system. For this early experiment, injections were used rather than oral formulations. Griebel explained that much of his work has been done using sheep as an experimental model for cattle. The information generated will also apply to cattle but for cost and housing purposes, sheep proved to be easier subjects.

Three groups of three lambs each were injected subcutaneously with either saline, adenovirus vaccine particles in saline alone, or adenovirus vaccine particles in alginate microspheres. A second injection was administered three weeks after the first. Ten days later, the lambs were euthanized.

To determine the effect of the vaccine, immune response was measured in the serum and blood throughout the experiment and in the lymph tissue after the animals were euthanized.

Immune responses were detected in group 3 lambs, the vaccine-plus-microsphere group, indicating that the bovine adenovirus vaccine vector was successfully released by the microspheres: a significant triumph for the researchers.

The degree of immune response, however, was much higher in the group that received the adenovirus vaccine particles in saline. The new vaccine formulation may need to be altered, or the amount of the active component increased, in order to make the new vaccine delivery system more potent.

The next objective for Dr. Griebel’s team is to immunize animals orally with the test vaccine.

Considerable work lies ahead before oral formulations are completed and proven to be effective. But eventually, the researchers believe, calves will be able to munch on their vaccines as part of a feed ration or mineral supplement.