The mysterious death of 21 champion polo horses last week left scientists stumped. There was no sign of foul play, and no obvious cause for the deaths. Now the leader of the Venezuelan-owned team has told an Argentine newspaper a supplementary vitamin is behind the mystery. The horses were given Biodyl, which contains a combination of vitamin B-12 and other minerals. Although not approved in the United States, the supplement is widely used elsewhere to help horses with exhaustion.

Listen to The Takeaway's earlier investigation into this tragedy.

For more, watch this video by the Associated Press.

The mysterious death of 21 champion polo horses last week left scientists stumped. There was no sign of foul play, and no obvious cause for the deaths. Now the leader of the Venezuelan-owned team has told an Argentine newspaper a supplementary vitamin is behind the mystery. The horses were given Biodyl, which contains a combination of vitamin B-12 and other minerals. Although not approved in the United States, the supplement is widely used elsewhere to help horses with exhaustion.

Listen to The Takeaway's earlier investigation into this tragedy.

For more, watch this video by the Associated Press.