If you look up Eco Research The Horse Project, you will find info on an equine cognition study. The horses in the study all know at least 200 words. One of them knows over 250 words and has learned some concepts. As far as linguistic intelligence goes,this would show that they are (at least) as intelligent as a toddler(I think a 2 yr old.)Dogs are said to be as intelligent as a 2 or 3 yr. old child.
Really interesting. Well-written. Reinforced some knowledge and offered new research-based information.
Fascinating article. I would be interested in seeing a intelligence comparison between the 3 companion animals.