Short answer. Yes. Article 1576 of the Civil Code treats a hidden defect in an animal as redhibitory, meaning it can support returning the animal, even where a professional veterinary inspection was made but expert knowledge simply was not enough to detect it. Undetectability by a vet does not defeat your right to return the animal.
What the law says
If the hidden defect of animals, even in case a professional inspection has been made, should be of such a nature that expert knowledge is not sufficient to discover it, the defect shall be considered as redhibitory.
Civil Code, Article 1576 — Redhibitory Defect Undiscoverable by Experts. Read the full provision →
Why undetectability does not defeat the remedy
It might seem that if even a veterinarian could not find the defect, the seller should be excused. Article 1576 rejects that logic. It says that where a hidden defect is of such a nature that expert knowledge is not sufficient to discover it, the defect is still considered redhibitory, meaning it still counts as the kind of serious hidden fault that supports rescinding the sale or reducing the price. The focus is on the defect actually existing and being hidden, not on whether it was realistically detectable beforehand by an expert.
What redhibitory means for your options
Calling a defect redhibitory ties it to the Civil Code's warranty rules against hidden defects in things sold, animals included. A redhibitory defect is serious enough, and hidden enough, that the buyer would not have agreed to the sale, or would have paid less, had the defect been known. Article 1576 confirms that this classification survives even a failed professional inspection, so you are not left without a remedy simply because a vet examined the animal beforehand and found nothing wrong with it at the time of the sale.
What happens if the vet was at fault
Article 1576 also addresses the veterinarian's own position: if the veterinarian, through ignorance or bad faith, fails to discover or disclose the defect, the veterinarian becomes liable for damages. This is a separate consequence from your remedy against the seller over the animal itself. It means a vet who examined the animal negligently or dishonestly, rather than an inspection genuinely defeated by an undiscoverable defect, can face liability of his own for that failure, apart from whatever you recover from the seller.
What this does not change about the underlying sale
Article 1576 does not, by itself, walk through every procedural detail of how or when a defect must be raised with the seller; it establishes that this kind of undetectable hidden defect still qualifies as redhibitory. The core requirement remains that the defect must have existed at the time of the sale and must be the kind of serious, hidden fault the Civil Code's warranty rules address, rather than an ordinary condition a buyer should reasonably have anticipated when acquiring an animal.