Two calves were beheaded in a vicious overnight farm attack thought to have been driven by the black-market meat trade.
The killers butchered the animals, leaving behind only their innards and heads, and draining the blood.
Several other calves were deliberately injured, in what experts suspect was an attempt to prevent them escaping.
The RSPCA says it believes the killers of the year-old calves were harvesting meat for the black market. The attackers did not stun the animals to numb them to pain.
A vet said another calf suffered a head wound and two more had deep gashes to their tendons – in a suspected effort to stop them from getting away. The RSPCA said the wounds from the attack were so severe that the two calves had to be put down to end their suffering.
The vet, who did not want to be identified, said: “This malicious act must have been carried out by someone with slaughter or butchery experience as they appeared to know how to dismember a cow.
“Without a handling system the calves were most likely chased and immobilised in the field by slicing the hindlimb tendons.
“There was no evidence of stunning to render them unconscious, so these animals were aware of the pain until the end.
“Once I examined the remaining calves, there were multiple laceration injuries to hind limbs. Those that were uninjured displayed signs of stress, exhaustion and abnormal calf behaviour for several days after.”
Investigators believe all the dead animals’ blood was taken little blood was found in the field, contrary to what would be expected.
The farmer, identified only as Mr Whiteman, said: “I can’t believe it. This is a wicked thing to do. I’ve worked with animals all my life and I’ve never seen anything like this – the cruelty of it is unbelievable. You look after and care for your animals so to see something like this happen is really upsetting.”
Inspector Fiona Howell, who is investigating for the RSPCA, said: “This is a shocking and concerning incident and would have caused the calves significant distress and suffering.
“Even if the person who did this is trained in slaughter, to kill two calves in an open field in the middle of the night without proper equipment, stunning or sedation, is inhumane and cruel.
“This must have taken several people to undertake and a large vehicle or van so we’re hopeful that someone will have seen or heard something which might help our investigation.”
She asked anyone who might have seen anything suspicious to ring 0300 123 8018, or contact the police on 101 quoting 91i.
Public health experts say black-market meat is unlikely to have been processed properly or subjected to quality checks and could be risky.