Burnie Magistrate Leanne Topfer convicted and sentenced TT-Line and Andrew Williams for their role in the deaths of 16 polo ponies following a Bass Strait crossing in January 2018.

It is more than five years since the transport of 18 horses inside Williams' truck and converted refrigeration trailer aboard the Spirit of Tasmania ended in the tragedy.

Williams pleaded guilty in July last year to 17 breaches of the Animal Welfare Act, while TT-Line pleaded not guilty to 29 breaches of the act but were subsequently found guilty by Ms Topfer following a three-week hearing.

The case has been dragged through multiple levels of the Australian court system as TT-Line sought to appeal a range of aspects of the case before it even got to hearing, and signalled it would appeal the guilty verdict and any subsequent sentence in the Tasmanian Supreme Court.

Ms Topfer said the company must have spent "a very significant amount of money" defending against the charges, and had failed in all its appeals so far.

Last year, The Advocate reported that TT-Line appeared to have spent millions in its defence of the charges.

The company's lawyers had submitted that it should be spared convictions on the charges as its reputation would be tarnished, but Ms Topfer said she did not see how not convicting would spare the company any reputation damage earned by her guilty verdict.

She convicted TT-Line of all charges and fined the company $75,000, or $4687.50 per horse.

As Williams was the driver of the truck, Ms Topfer said his moral culpability was greater than TT-Line's, but accepted there were mitigating circumstances.

She said he was unable to inspect the horses during the journey and had successfully transported horses in that trailer aboard the Spirit of Tasmania eight times in the previous two years.

She also said his guilty plea was indicative of his remorse, and that he was "devastated by the incident, which exacted an immediate and heavy emotional toll".

Williams has been the subject of media interest for five years, and had been abused on social media and sought mental health care.

Ms Topfer said Williams was a 49-year-old father of three and she had "no doubt this has put an enormous stress on your family".

However, she said he "failed in your duty to those animals."

She convicted Williams of all charges and fined him $15,000.

For each of the 16 dead horses, a fine of $5625 was imposed on both parties.