Madrid: The incident took place in Cadiz where the painted donkeys were filmed grazing close to a bar in El Palmar town while celebrations were going on.
A concerned local filmed the animals and reported the incident to animal rights activists.
Angel Tomas Herrera Pelaez, who filmed the donkeys, termed the sight as "shameful" and shared the video and the images in a Facebook post which has now gone viral.
His post prompted other netizens to criticize the mistreatment of the animals.
One user wrote, "You had to paint them for the wedding? This type of activities makes me very embarrassed to think that I belong to the same species."
"I have not seen it with my own eyes, but come on, I will not see it either, because my face would fall out of shame. If someone is going to promote some action, please keep them informed," wrote another.
The matter was brought to the attention of the Agrarian Regional Office of Medina Sidonia as well as the Nature Protection Service of Spain. An investigation into the incident was launched.