Sean McKay, 19, was on bail when he attacked the dog, named Hooch, with a blade.
He lashed out after falling out with girlfriend Melissa Johnstone and two women on February 5 in Girvan, South Ayrshire.
McKay denied two charges, of behaving in a threatening and abusive manner to the three women by shouting and swearing before deliberately injuring the dog, and causing a protected animal unnecessary suffering by repeatedly striking him on the body with a knife.
But a jury saw through his lies and convicted him at Ayr Sheriff Court.
Defending, Paul Feeney said: "When not in custody he has resided with his aunt who is a responsible lady who works in a charity shop.
"He is welcome back at her house and she can provide a suitable address."
"Mr McKay is considered suitable for a community based disposal.
"This is the second report in a short period where he has been deemed suitable for this but is not suitable for unpaid work due to health difficulties."
Sheriff John Montgomery sentenced McKay to nine months' detention in a Young Offenders Institution on one charge of threatening and abusive behaviour which included a period for committing the offence while on bail.
He was sentenced to a further 15 months for stabbing the dog which will run consecutively.