Alun Titford, 45, of of Colwyn, Newtown, denies the charge along with an alternative charge of causing or allowing the death of a child or vulnerable adult.
Teenager, Kaylea Titford, who had spina bifida and had become morbidly obese, died aged 16 in October 2022.
In her closing speech on Thursday, prosecuting KC Caroline Rees told the jury at Mold Crown Court that Alan Titford knew full well his daughter’s living environment was dirty and unhygienic.
"He took not a single step to improve it," she said.
In the last weeks or months of her life, Kaylea allegedly lay immobile in her bed through lockdown, unable to keep herself hygienic. She had not seen a doctor for nine months, the court has been told.
Ms Rees said Kaylea couldn’t access her bathroom and toilet and lay in her own human waste.
“It must have been an entirely wretched experience which you wouldn’t wish on any animal, let alone a vulnerable disabled child,” she said.
“She deserved and needed love, care and personal dignity and had a right to expect it from those who should have cared for her most, both her parents.
"But they seriously and grossly failed in caring for their daughter.”
Ms Rees said Kaylea’s body was found “in circumstances so grim, so revolting, even experienced police officers had seen nothing like it before”.
Kaylea’s mother, Sarah Lloyd-Jones, 39, has pleaded guilty to manslaughter by gross negligence.
Judge Mr Justice Martin Alexander Griffiths was due to hear the defence closing speech on Friday.