It should be relocated at Horse because there's been considerable evidence to suggest that the species on Earth and Mondas were identical, down to Mondasians often being called Human. While such pages as Lizard King and Silurian make sense to keep apart due to them illustrated to be seperate, I see no justification to presume that a horse from Mondas isn't the same as any regular ol' horse without substantial evidence.
Talk about it here or check the revision history for additional comments.
By the time that the Fifth Doctor and Nyssa visited Mondas, such horses had been augmented with cybernetic parts and were ridden by the partly cyber-converted police officers on Mondas. (AUDIO: Spare Parts)