A castrated horse is typically a male horse (Stallion or colt) that has had its reproductive organs (testicles) removed to prevent it from being able to breed. A castrated h … orse is called a gelding. A castrated horse, in male horses would result in them being geldings or unable to reproduce.If you castrate a stallion, you'll have a gelding left. For mares it's just you make them unable to reproduce. Much like a spaying or neutering a cat, except for horses. castrated h … orse is called a gelding. A castrated horse, in male horses would result in them being geldings or unable to reproduce. If you castrate a stallion, you'll have a gelding left.