The horse was for his use.

If he could be his own bed-maker, cook, and groom, it was evident that he would lack for nothing.

A man whom Madame Le Maitre sent showed Caius his quarters, and delivered to him the key; he also said that Madame Le Maitre would be ready in an hour to ride over the island with him and introduce him to all the houses in which there was illness.
Caius was left for the hour to look over his establishment and make friends with his horse.

It was all very surprising..