Good job, whmcheryl. Your plan is very succinct and clear. I like it.
But perhaps you want look at both sides of the problem.
There are also a few problems which are brought about by keeping animals in cage. For example, as you say,
Keeping animals in cages increase the chances that they do not go into extinction.
However, keeping them in cages, at the same time, deprives the animals from its natural habitats. And it leads to many serious consequences. For ex, the animal losses its natural instinct or becomes weaker and more vulnerable to diseases.
And perhaps, you want to add in some suggestion. For example, instead of keeping them in the cages, we should keep them in a huge safari which provides a similar environment to their natural habitat. And there, different types of animals can interact with one and another.
All the best to your essay.