When the cameras triggered an alarm on the evening of January 22, a trainer saw Webb-Jackson opening a number of stables and called the police.
Police found Webb-Jackson crouching in the corner of a fourth open stable, where he was arrested after a short scuffle with police and taken to Grafton police station.
During police interviews Webb-Jackson admitted to committing two sexual acts with a horse.
He told police the filly smelt his crotch and winked at him, which he believed was the animal giving consent, The Daily Examiner of Grafton reported.
The trainer said he was preparing the horse to race, but the incident had changed the demeanour of the animal dramatically.
"She is only a little two-year-old and we had to put her out in the paddock," the trainer said.
"The filly went from being quiet to just being highly strung, she changed in 24 hours. We had to put her in the paddock to try and get her head right.
"You don't want to see this sort of thing happening, it's really sick stuff."
In her judgment, Magistrate Karen Stafford said the basis of the animal cruelty act was to ensure humans protected the welfare and the manner of treatment of animals, and the definition of cruelty must be considered in light of the objective of the act.
She said the two sexual acts — allowing a horse to fellate Webb-Jackson and digitally penetrating the horse — amounted to acts of cruelty.
Webb-Jackson was jailed for 10 months with a non-parole period of four months and was also fined $700. With time served, he will be eligible for release next week.
