Wind-sucking bears a close analogy with Crib-biting[…], it arises from the same causes, and the same results follow. The Horse stands with his neck bent, his head drawn inward, his lips alternately a little opened and then closed, and a noise is heard as if he were sucking[…]. It is a Vice.
Source: wiktionary
Cribbing is scarcely a disease, though it may be productive of disease of the larynx. It is a habit usually acquired by young horses, either in idle moments or by imitation, often from the dam. The colt takes any wooden substance, such as a paling or manger, between his teeth and gnaws it. From that he proceeds to inhale the air, and often, when this habit has been acquired, he becomes a windsucker. It is probable that windsucking produces irritation in the throat and air-passages, and may lead to some enlargement, and consequently to roaring; but it is more probable that windsucking is the effect of disease.
Source: wiktionary