What is the definition of "novel protein"?

In the pet food industry, a novel protein is a protein source that the pet has never eaten before. Novel proteins are used as pet food for animals that have developed allergies to common protein sources.

Pets such as dogs and cats are often fed diets consisting of chicken, beef, lamb and fish. If an intolerance develops, it may be hard to discern exactly what ingredient causes the problem. For these pets, offering a diet consisting of novel proteins such as bison, duck, rabbit, fish they haven't eaten before, venison, kangaroo or egg, either alone or with a single carbohydrate source such as potato or rice, can help resolve the problem.