IT killed 12 dogs and left at least two others seriously ill – but the cause looks set to remain a mystery.

Scientists have failed to identify a deadly toxin that resulted in dogs suffering acute kidney failure after being taken for a walk in the New Forest.

Hazardous chemicals and other potential causes have been ruled out, leaving experts baffled.

The investigation involved a number of organisations including New Forest District Council, the Forestry Commission, the Animal Health Trust and the Environment Agency.

They joined forces after dogs started succumbing to a water or soil-borne poison that may have been disturbed by weeks of heavy rain.

A council spokesman said: “Despite extensive testing, the underlying cause unfortunately remains unknown.

“The affected dogs all developed sore/lesions on their legs within three to seven days of their walk and went on to develop acute kidney failure.

“All the more common causes of kidney failure were excluded in all of the dogs.

“Further investigations have been performed on blood, urine, faeces and postmortem tissue. This included bacterial, including e-coli, viral and heavy metal testing.

“Kidney tissue has been examined by a number of veterinary pathologists and specialist human kidney pathologists. Testing for hazardous chemicals in the New Forest was also performed.”

Dogs started falling victim to the mystery toxin last December and the spate of deaths continued for several months.

Most of the incidents occurred in the same part of the Forest – a vast expanse of heathland between Fritham and the Ringwood- Fordingbridge area.

The last confirmed case was reported in April and involved a dog that had been exercised near Burley.

As reported in the Daily Echo, a Jack Russell called Squibby is one of only two pets known to have survived the toxin. She suffered a swollen paw after going for a run near Latchmore Brook and spent nine days on a drip.

No other animal species appears to have been affected by the poison.

The mystery took a new twist earlier this year after it was revealed that similar cases had been reported in other parts of the country, including Cornwall, County Durham and Surrey.

A three-year-old dog called Gemma died in August after being exercised near Ringwood, but the incident is not being linked to the others.

Despite the six-month gap since the last confirmed case, dog owners in the Forest are being urged to stay on their guard.

The council spokesman said they should seek veterinary help if they spotted a wound, lesion or blister on their pet’s legs or face.