Dog: kennel: : : stable horse alfalfa steady manger

The answer is horse:stable.

Explanation:

We must find the logic behind the connection between the first two words so that we can complete the second pair.

In the "dog:kennel" relationship, we have an animal and a shelter where that specific kind of animal usually stays. Thus, by following the same logic, in the "blank:stable" relationship, we can notice we have only the second word, which is the shelter where a specific kind of animal stays. We are missing the animal. A stable is a shelter for horses. We may conclude, then, that the animal that is missing in the pair is "horse.