Farmer Jonathon Court and his family have been praised for their swift action.
He noticed suspicious symptoms in some of his chickens on Monday night and immediately notified the Department for Food and Rural Affairs.
Defra today confirmed the outbreak was the highly contagious H7N7 strain.
The outbreak was officially confirmed by officials on Tuesday night.
So far no other birds within the three-kilometre protection zone around Eastwood Farm, between Shenington and Shutford - about 10 miles west of Banbury - have shown signs or symptoms of Avian Flu.
A cull of 25,000 chickens at the farm concluded yesterday and the area is being disinfected. Once that is completed, Defra officials will leave the site.
Over the next few days, experts will visit farms and smallholdings within the protection area to conduct further tests.
A Defra spokesman said: "We have been in contact with other farms and there have been no warning signs of other birds with symptoms."
Praising the Court family, the spokesman said: "He was obviously a very vigilant farmer, who checked his stock regularly. When he knew something was wrong, he took it straight to the vet himself.
"While he was waiting for the results to come through, he kept all the chickens inside.
"He did all the right things. Hopefully, that would have had an impact in keeping it contained.
"It's definitely down to the quick thinking and vigilance of the farmer."
One lorry of carcasses was taken from the site last night to be incinerated at an unspecified site and a second left last night.
A 10-kilometre surveillance zone is still in place around the farm - restricting the movement of birds and their produce.
The Government's Chief Vet, Nigel Gibbens, said the H7N7 strain had been detected in domestic poultry and wild birds elsewhere in Europe.
An investigation is now under way to trace possible sources of the outbreak.
Wardington-based specialist firm Omlet, which supplies chicken farms with birds ready to lay, said although it was outside the surveillance zone, it had taken protective measures. The firm keeps between 400 and 800 chickens on site.
Co-founder Johannes Paul said: "We always have really good bio-security and are being good about looking after our chickens.
"We will do whatever is necessary and have the facility to keep them inside."
A team from Oxfordshire County Council's trading standards department has been involved in shutting public footpaths and rights of way around the protected zone.