Wayne Bryson has pleaded guilty to “engaging in an act of sexual penetration” with four-year-old Staffordshire Bull Terrier Rudy.
The 19-year-old’s shocked girlfriend Amber Hickling, 18, was looking for photos of their child on his phone when she spotted the sick footage of him sexually assaulting her pet.
She handed the phone to police and Bryson, who worked at a recycling plastics factory, was arrested the same day.
He could not explain his behaviour to police but claimed it "only happened once".
The teen received a four month prison sentence, suspended for two years, and was ordered to sign the Sex Offenders’ Register for seven years. The maximum sentence for the offence is two years imprisonment.
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He was also told he must never be alone with any animal again.
Speaking after the sentencing, Amber, from Louth, said: “When I found the video I felt sick. I was shaking and crying. I just couldn’t believe it. I would have been surprised to catch him cheating, but to catch him shagging my dog was wrong on a different level.
“When I heard the sentence, I was very upset. I think he should have got a much harsher sentence... because it’s a dog that couldn’t even defend itself he’s free.
Amber also revealed that she is seeking counselling and has been forced to re-home Rudy because she cannot bear to “look her in the eye.”
She added: “When I looked at her all I could see was what Wayne did. She wasn’t the same dog. She was frightened and cowering. I couldn’t stand to look at her so I found a family to re-home her with."