Hindus protested outside the RSPCA's headquarters in Horsham over the slaughter of a sick sacred cow at their temple.

The animal charity was accused of secretly killing Gangotri, a 13-year-old Belgian Blue Jersey cross, by lethal injection at Bhaktivedanta Manor in Hertfordshire.

The RSPCA emphatically denied the allegation, saying it found staff on the site and told them exactly what they were doing before the animal was put to sleep.

Temple spokesman Vinay Tanna said: "We are holding a peaceful prayer protest at the way Gangotri was killed. The RSPCA made the equivalent of a citizen's arrest - they went in and made the decision to kill the cow immediately. Given the chance, we would have taken legal action to try to stop it."

The temple sent scores of delegates to the RSPCA headquarters in Wilberforce Way, Southwater, to protest.

Meanwhile, a religious ceremony to mark the end of the mourning period for the cow was attended by 700 Hindus at the temple. Mr Tanna said: "The killing of a Hindu cow in the temple is very inauspicious indeed." Cows are sacred to Hindus and killing one is considered sacrilege.

Hindu community leader Gauri Das said police bundled away monks attending to the sick cow. The head farmer was kept talking while a lethal injection was administered inside the barn.

He said the cow was sick but had no disease and was being cared for by temple residents and visiting worshippers. The temple runs The Cow Protection Project and allows old cows and bulls to die naturally.

The RSPCA said it was "sympathetic" towards the representatives of Bhaktivedanta Manor but its first consideration was animal welfare.

The charity said the cow was put to sleep under veterinary supervision and the method used was humane and caused the cow no extra suffering. In a statement, it said: "We knew the cow has been suffering from painful and infected sores, her limbs had become wasted and her breathing difficult.

"Three separate vets, including from the Royal College of Vets, from Defra and an independent vet, all agreed the animal was suffering and should be immediately euthanised.

"The allegation of a history of mercy killings is entirely unsubstantiated. The RSPCA puts animals to sleep as a last resort and then only to prevent them from suffering further.

"We categorically deny any deceit. We found staff on the site and told them exactly what we were doing.

"We actually took advice to prevent our visit happening at prayer time."