Meat inspectors at an abattoir linked to the E.coli outbreak in 2005 did everything they could to protect public health, an inquiry has heard.
JE Tudor slaughterhouse in Rhondda has the worst hygiene record in the UK in the 1990s and contamination problems went on until after the fatal outbreak.
But veterinary director Jane Downs said meat hygiene inspectors had been "diligent" in their duties.
It is the final day of hearings of the six week public inquiry in Cardiff.
The inquiry has previously heard damning evidence about the slaughterhouse in Treorchy, Rhondda which was run by a cousin of William Tudor, the Bridgend butcher later jailed for hygiene offences related to the outbreak across schools in the south Wales valleys.
The inquiry has heard that the abattoir was allowed to keep operating until 2006 despite recommendations to close it down as far back as 1994.
It has also heard vets inspecting the slaughterhouse in the years before the health outbreak were advised to "adopt a light touch" in dealing with its owner.
On Wednesday, Mrs Downs from the Meat Hygiene Service defended the inspectors and said the enforcement actions they undertook was reasonable.
A series of inspection reports show repeated problems between 2003 and 2005 , which made the abattoir impossible to clean, and allowed flies to buzz around carcasses, the inquiry heard.
That was despite the fact there was a one-on-one ratio of inspectors monitoring staff.
Five-year-old Mason Jones from Deri, Bargoed, in the Rhymney Valley was the only person to die in the outbreak, but more than 150 other children and adults became ill.
The boy's mother said she was shocked by the evidence she has heard.
Sharon Mills said "Myself and my family have sat through the full six weeks of the oral hearings of the public Inquiry and the evidence we have heard has been quite horrific.
"To know this outbreak was so avoidable has made it even harder to ever come to terms with Mason's death."
The family have been particularly upset by what they see as failures in the inspection system, and the process of meat procurement in schools.
"Why weren't complaints acted upon?" asked Ms Mills.
"Why was Tudor given the contract?
"The procurement process failed drastically and we have serious concerns about the inspection regime. It's obvious that neither process was good enough."
The inquiry has heard how butchers John Tudor and Son of Bridgend had supplied schools in the south Wales valleys for almost a decade before meat from its plant carried E.coli through the food chain.
The public inquiry, chaired by microbiologist Professor Hugh Pennington, is due to reconvene on 14 May and will take written evidence in the meantime.