Short answer. The sale is void. Under Article 1575 of the Civil Code, when the intended use of an animal is stated in the contract and the animal turns out to be unfit for that purpose, the contract of sale is void from the beginning — not merely rescindable, but void.
What the law says
A contract of sale of animals shall also be void if the use or service for which they are acquired has been stated in the contract, and they are found to be unfit therefor.
Civil Code, Article 1575 — Void Sales of Animals. Read the full provision →
Void, not merely rescindable
The Civil Code is deliberate here: Article 1575 says the contract of sale shall be void. Void means the contract is treated as never having existed — it produces no legal effects from the start. This is more powerful than rescission, which undoes a contract that was initially valid. Because the stated purpose was part of the very object of the contract, an animal that cannot meet that purpose fails the contract at its foundation. You do not need to sue to rescind; the contract is already legally ineffective.
The stated purpose must appear in the contract itself
The rule applies only when the use or service for which the animal is acquired has been stated in the contract. If you bought a carabao and the deed of sale or written agreement expressly says it is for farm plowing, and the animal cannot plow, Article 1575 kicks in automatically. If the purpose was only discussed verbally or assumed but never written into the agreement, this provision may not apply as directly — though other rules about warranty and hidden defects may still help you. The written or documented statement of purpose is what triggers this specific remedy.
The article also voids sales of contagious animals
Article 1575 covers two separate situations. The first — and more sweeping — is that the sale of animals suffering from contagious diseases shall be void. You do not even need a stated purpose for that ground; a contagious disease at the time of sale voids the transaction regardless. The second is the stated-purpose rule described above. Both lead to the same result: a void sale. If your animal was both diseased and unfit for its stated purpose, either ground is sufficient — you do not need to argue both.
What follows from a void sale
When a sale is void, the parties must restore each other to their original positions. You return the animal; the seller returns the price you paid. If you suffered losses because of the animal's unfitness — veterinary costs, lost labor, damage to other animals — you may have additional claims depending on whether the seller knew of the defect. Document your situation thoroughly: the contract language stating the purpose, evidence that the animal cannot perform that function, and any losses you incurred while trying to use it. These records support whatever legal steps you take.