Short answer. Yes. When a sale of an animal is rescinded, the law requires you to return it in the same condition it was sold and delivered. Any injury caused by your own negligence is your liability — you must account for it, which reduces what you can recover from the seller.
What the law says
the animal shall be returned in the condition in which it was sold and delivered, the vendee being answerable for any injury due to his negligence, and not arising from the redhibitory fault or defect
Civil Code, Article 1579 — Return of the Animal on Rescission. Read the full provision →
What the law says about returning the animal
Article 1579 of the Civil Code sets a clear baseline: if a sale is rescinded, the animal goes back in the same condition it arrived. The buyer is accountable for any harm to the animal that stems from his own negligence. The exception is injury that flows from the very redhibitory fault or defect that justified rescission in the first place — those injuries trace back to the seller's problem, not yours.
How negligence affects your recovery
Rescission is meant to put both parties back where they started. If the animal was worth a certain value when delivered but is now worth less because you mishandled it, that difference is on you. In practice, the court assesses the animal's condition at the time of sale compared to its condition at the time of return. Losses traceable to your careless handling — improper feeding, rough use, delayed veterinary care — will be offset against whatever you are claiming back from the seller.
The dividing line: your negligence or the seller's defect
The statute draws a sharp distinction. Injuries arising from the redhibitory fault or defect — the hidden condition that made the animal unsound in the first place — are the seller's problem. Only injuries due to your own negligence fall on you. So if the animal had a hidden illness that worsened on its own, you are not liable for that deterioration. But if you let it run loose and it broke a leg, that is yours to answer for. Where the cause of the injury is disputed, the facts of how you cared for the animal during your possession will matter.
What this means practically
If you are in the middle of a rescission dispute, document how the animal was kept from the day you received it: feeding logs, veterinary visits, housing conditions. Clear records make it easier to show that any decline in the animal's health was caused by the pre-existing defect — not by anything you did. If there genuinely was some carelessness on your part, it is better to acknowledge it and argue the amount than to dispute liability entirely. A lawyer can help you quantify each cause and negotiate with the seller before the matter reaches a court.