Q:

'Which' applied to brute animals

I found the phrase “... the horse which ran was not the horse nor of the age which he was represented to be at the time of entry ...” in a sentence of Codes, Rules and Regulations of the State of New York 9 Executive (E) - Chapter 1, Subchapter A : State Racing Board Thoroughbred Rules, 4039.19. [→]
Is which wrong in the phrase above, or is it the exact word as the horse is a brute animal?
To be clear, which is grammatical : "... the horse which ran ..." or "... the horse who¹ ran ..."?
¹ See the following nGram for "cat who" (cat: no brute), "dog who" (dog: no brute), "horse who" (horse: brute) and "bull who" (bull: brute).

A:

I agree that that sounds best.
To quote Building English Skills (McDougall, Littell, and Company):

The pronouns which and that also require special attention. Use
  that to introduce adjective clauses that are essential to the sentence. Use which to introduce nonessential clauses.

There is the painting that he loves so much. (that he loves so much is essential to the sentence.)
The painting, which he loves so much, is not for sale. (Here, the clause is not essential to the sentence.)

(Littell, Joy. "Sentence and Clause." Building English Skills: Yellow Level. Evanston, Illinois: McDougal, Littell & Co., 1985. 528. Print.)
In the sentence mentioned, it should be that, as the sentence qualifies the horse. It shows that the horse you're referring to is the one that ran, perhaps singling it out from a group of other horses that did not. You're not simply describing it, noting that it ran, as you would be were the sentence "The horse, which ran, ...".
Also, a clause containing which should be separated by commas: "The horse, which ran, ...", which is not the case for a clause containing that: "The horse that ran..."

A:

In our veterinary publications, we don't generally use "who" as a pronoun for animals. (In fact, we avoid "his" and "her," too.) Exceptions might be made when the animal is named and the publication's intended audience is the pet owner. I agree with cornbread ninja's comment that the which in both places should be that. Based on the given excerpt, these appear to be restrictive clauses.

