Horses no longer open their mouths while grazing

Horses no longer open their mouths, but the sound they make when they open their mouth is still present. Usually right after you spawn a horse or the horse is idle you will see these animations followed by the sound they make when they open their mouths.

Steps to reproduce

• Spawn a horse (via spawn egg)
• (The neigh or something) sound plays but the horses mouth never opens.
• Notice that the horses' mouth never opens every time you spawn a horse or when the horse is idle.

What animation I'm talking about?

• Hit the horse.
• Notice the horses mouth just opened.
• This animation isn't being shown when ever you hear the (neigh or something sound.)