Alan Barnfield, 44, was accused of having sexual intercourse with a pony called Sky in a field near Doncaster, South Yorkshire, in 2012.
Judge Peter Kelson QC told Barnfield he believed the jury had come to the verdicts it had because it believed a sexual incident with the animal took place in the field but could not be sure that actual sexual intercourse had occurred.
Judge Kelson suggested it was possible that horse DNA got on to the defendant’s penis if he was masturbating while abusing Sky in a different way, including with a cider bottle.
The judge pointed out that, while the outraging public decency charge was only added halfway through the trial, it actually carried an unlimited sentence whereas the main charge he was cleared of — intercourse with an animal — carries a two-year maximum.
The second charge was added when lawyers in the case realised Barnfield could only be found guilty of the central charge if he had actually inserted his penis into the animal and that he would have to be acquitted if this could not be proved.
Judge Kelson said the case was “unique and repulsive” and that Barnfield has an “utterly disgusting perversion”.
Prosecutors told the jury at Sheffield Crown Court police were called to a field near the village of Loversall, South Yorkshire, in the early hours of August 8, 2012.
Officers spoke to Barnfield because concerned residents thought he may have been trying to steal Sky and another pony in the same field, Savannah.
Later, after both animals were found to be injured, Barnfield was arrested and horse DNA was found on his penis.
He told the jury he was just out for a walk and had only stroked and fed the bigger pony, Savannah. He also claimed he carried three cans of deodorant because his medication made him sweat and not, as prosecutors claimed, to take away the “horse smells” after his abuse of the animals.
The police said the defendant smelt strongly of horses and was sweating profusely.
In a victim impact statement read to the court, Sky’s owner, Jodie Walters, said the pony’s personality changed after the incident.
Ms Walters said the pony would shake and tremble when she was led near where the attack happened and “would just stare as if she was fixated on something”.
She said she eventually had to give Sky away so she could have a “fresh start” somewhere else — something which was “heart-wrenching” for her six-year-old son.
The court heard Sky had serious injuries to her genital areas to the extent that a vet had to subdue her before he could even lift her tail.
Judge Kelson told Barnfield: “The jury are sure the incident overall occurred. But they are not sure that you inserted your penis into the Shetland pony called Sky.”
He added the verdicts were “wholly understandable”.
The judge said he was sure Barnfield used a cider bottle for part of the abuse and that he tried to lead away the other horse, causing her injuries too.
The judge apologised to the jurors for the nature of the evidence they had to sit through during the week-long trial.