Parents who locked their son in a room, banned him from speaking and fed him old food have been jailed.
The couple, who cannot be named, were found guilty of five child cruelty charges last month.
The boy was also beaten, he had to defecate on the floor, and he shared a broken mattress with his brother.
A judge at Northampton Crown Court sentenced the boy’s father to seven years in prison and his mother to three and a half years.
The trial related to events between 2012 and 2016. Professionals described it as the worst case of child cruelty they had seen in 25 years.
The case came to light when two of the boy’s sisters told one of their school teachers about him defecating in the house, and the teacher informed social services.
Prosecutor James Armstrong-Holmes had said this was a case involving serious neglect and a “deliberate disregard for the welfare of the victim”.
‘Nothing short of depraved’
In mitigation, defence barrister Andrew Fitch-Holland, said the boy’s father had simply been overwhelmed by events, and insisted he had not been driven by malice.
Barnaby Shaw, speaking on behalf of the boy’s mother, told the court she had been a secondary partner in the abuse and did not have control over events in the house.
The couple had a large, undisclosed, number of children. They youngest have been adopted, and the rest are in care.
Sentencing, Judge Michael Fowler said the father had told “obvious lies”.
He also criticised the way the couple had used one bedroom and just two beds for four of their children.
Det Con Nicky Webb, from Northamptonshire Police, said: “In 20 years of working in child protection I have never before encountered abuse and neglect on this scale.”
An NSPCC spokesperson said: “For a mother and father to lock up their own child, make him sleep in his own excrement and force his siblings to beat him is nothing short of depraved.”
A Northamptonshire County Council spokesman acknowledged the “difficult and serious nature” of the case and said “significant changes” had been made to systems and practices as a result of its work with the Children’s Commissioner.