Horses don't typically growl like dogs. It's possible you're misinterpreting the sound. Horses might:
* Snort: This is a way for them to express excitement, nervousness, or a warning.
* Neigh: A typical horse communication sound, usually used to call for other horses or for attention.
* Whine: A softer sound, often used to express discomfort or hunger.
* Make other noises: Horses can make a variety of sounds depending on their mood and situation.
If you're concerned about your horse's behavior, it's best to consult a veterinarian or an experienced horse trainer. They can help you understand what your horse is trying to communicate and determine if there's an underlying medical issue.