Which of the following is NOT used as a form of identification for horses?

Ear notching is not a recognized method of identification specifically for horses. While it is commonly used in other species, such as pigs and cattle, to identify individual animals, horses typically do not have their ears notched for identification purposes.

The other methods listed—branding, tattooing, and microchipping—are prevalent forms of identification in horses. Branding involves marking the horse's hide with a unique symbol or letter, tattooing is often done in the lip or other areas to provide a permanent identification, and microchipping involves implanting a small chip under the skin that can be scanned for identification. All three methods are widely accepted and utilized in the equine industry to ensure accurate identification and ownership verification.