All objects have the potential to be edible. Much tast-testing and chewing is required to discover this potential. Other horses make interesting noises when you nip them. People make interesting noises when your place your foot on theirs People also make interesting noises when you buck while they are sitting on your back. The higher the buck, the louder the noise.
Mares find stallions very attractive.
Remind them of this as often as possible. Ignore any rude remarks, or respond with one of the above techniques for regaining control of the herd. Food was meant to be eaten and water was meant to be drunk. Nothing can change this fact. The more barriers in the way, the more number 26 applies.