In a nine-second Snapchat video emailed to CBC News, a man is seen approaching Misty the horse and owner Zsa Zsa Stiasny in a trailer before the wedding, then putting his hand out to feed the horse.
Snapchat allows users to write or draw on videos before posting and this video caption says "feeding the horse weed #thebadguy."
The man shooting the video and narrating says: "He's going to go feed the horse some weed ... He just gave the horse weed."
On Wednesday, we asked the horse's owner, Stiasny, about the video. She had not yet seen it and denied anyone fed her horse.
"She wouldn't touch it anyway. There's no way — she wouldn't eat it — horses are way smarter than that."
On Thursday morning, Stiasny called CBC News and said she had now seen the video and was shocked.
She believes Misty was given marijuana by a man who had asked to feed her horse.
"I thought he was feeding her grass or alfalfa," she said.
"I think in fact he did feed it weed. It's possible it contributed to the horse getting all reactive."
'Maybe it did make her go loco'
Stiasny believes the video was filmed about an hour before the ceremony and said the alleged marijuana incident could explain why her horse acted up.
Stiasny's horse Misty was supposed to carry a Sikh groom to his wedding last Saturday. During the procession, the horse appeared to be uncomfortable, eventually bolting from its handler and tossing the groom off its back.
"She was totally out of character, that was not how my horse behaves," she said.
SPCA investigating alleged cruelty
The SPCA tells CBC News it has launched a cruelty investigation into the incident.
"We can try to investigate to see who did this," said senior animal protection officer Eileen Drever.
But Drever said Stiasny also has a duty to protect her animal.
Do you have more to add to this story? Email Bal.Brach@cbc.ca