Dale Kunath pleaded guilty to two counts of aggravated assault on Friday. (Global Calgary)

Dale Kunath of High River pleaded guilty in a Calgary courtroom on Friday to two counts of aggravated assault on a six-week-old boy.

Kunath, 28, was charged after paramedics responded to a call about a child in distress at a house in southwest Calgary in June 2010.

He admitted in court that he brutally injured the infant as an act of retaliation against the baby's mother.

Kunath was charged initially with one count of aggravated assault and one count of aggravated sexual assault, but that was changed to a second count of aggravated assault despite the fact that Kunath sodomized the infant with an object and the baby's penis was torn.

The Crown and defence lawyers agreed his intent was to cause pain and not sexual in nature.

"This is a very significant child abuse case," said crown prosecutor Jamie Williams Friday, and the crown will be seeking a significant jail sentence.

Williams says this is the worst case of child abuse she has dealt with.

Doctors have not been able to determine whether the baby will face any long-term effects from his injuries.