Short answer. You can return the whole team. Article 1572 of the Civil Code provides that when a team is bought, the presumption is that the buyer would not have purchased the sound animals without the defective one — so the redhibitory defect of one gives rise to redhibition of the entire team.
What the law says
If two or more animals are sold together, whether for a lump sum or for a separate price for each of them, the redhibitory defect of one shall only give rise to its redhibition, and not that of the others; unless it should appear that the vendee would not have purchased the sound animal or animals without the defective one. The latter case shall be presumed when a team, yoke pair, or set is bought, even if a separate price has been fixed for each one of the animals composing the same.
Civil Code, Article 1572 — Redhibitory Defect When Several Animals Are Sold. Read the full provision →
General rule: only the defective animal is returned
Article 1572 of the Civil Code establishes the starting point for redhibition when several animals are sold together: If two or more animals are sold together, whether for a lump sum or for a separate price for each of them, the redhibitory defect of one shall only give rise to its redhibition, and not that of the others. The general rule is that each animal stands on its own. A defect in one does not automatically infect the others. The buyer's remedy for the defective animal is to return that animal and recover the corresponding price — the sound animals are not part of the redhibitory action.
Exception: the buyer would not have taken the others without the defective one
Article 1572 creates an exception: the defect of one can trigger redhibition of all if it should appear that the vendee would not have purchased the sound animal or animals without the defective one. This exception recognizes the economic reality of certain purchases. If the buyer bought the animals as a group and the group's value depended on having all of them together, separating them defeats the purpose of the purchase. The question is whether the buyer would have purchased the sound animals in isolation — if not, the animals form an interdependent unit and the defect in one grounds the return of all.
The team presumption: it applies to you
For the situation you describe, Article 1572 contains a specific presumption: The latter case shall be presumed when a team, yoke pair, or set is bought, even if a separate price has been fixed for each one of the animals composing the same. When the animals were purchased as a team, the law presumes that the buyer would not have taken the healthy ones without the defective one. You do not have to prove that you would have declined the individual animals — the law makes that inference automatically from the nature of the purchase as a team. The fact that each animal had a separate price does not change this.
What redhibition of the whole team means
If redhibition of the whole team is available, you may return all the animals and recover the full price you paid for the team. The seller must accept the return of the entire group, not just the one animal with the defect. This makes practical sense for work animals that function as a coordinated unit: a team of draft animals, for example, loses much of its utility if one is removed. The law's recognition of this practical reality through the team presumption aligns the legal remedy with what the buyer actually needs. You purchased a team, and a team with a defective member may be worth far less or unusable — returning the whole team and getting your money back is the appropriate remedy.