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Vets who were sent to the farm outside Balclutha, where 22-year-old Simon Wimoka Larsen worked, said the injuries were very rare and "would cause severe pain and suffering to the animals".
Larsen, who was second in charge at the 314-ha farm, appeared in the Dunedin District Court yesterday after pleading guilty to two charges of ill-treating an animal and two of reckless ill-treatment.
In November 2017, the vets and a Ministry for Primary Industries official inspected the 600-strong herd during milking.
The shocking injuries were clearly apparent in some cases.
A few cattle had open fractures of the tail, emitting a "purulent discharge".
"This type of injury required an extreme amount of force to be applied to the tail in order for the bone to pierce the thick skin," a report said.
Other animals had the end of their tales "degloved".
Another staff member at the farm explained Larsen would tie the tail to a rail then when the heifer was startled and jumped, they suffered a traumatic amputation.
At least three others exhibited similar tail loss.
Massey University professor of production animal health Richard Laven said it was unlikely the injuries had been caused simply by twisting or bending.
"This is more akin to a human dislocating their finger, except that it requires significantly more force," he said.
"The tail in dairy cattle is a very important and sensitive organ. It's primary use is to control flies, but it is also used in social signalling and in cow-cow interactions."
When Larsen was confronted, he admitted to having "anger issues".
He claimed he had previously been taught to "use the tails like a steering wheel and push them up" but conceded "some that I've yanked, gone a bit too hard and I've felt the crunch and the crack and it's not good".
Larsen admitted wrapping one heifer's tail around a bar to calm the cow down.
Defence counsel Meg Scally said her client suffered mental health issues and was embroiled in some conflict with another staff member at the time.
"He wasn't doing it for the sake of being cruel," she said.
Judge Michael Turner sentenced Larsen to two months' community detention, 240 hours' community work and nine months' supervision.
He was ordered to pay vet costs of $1852 and banned from having any involvement with animals for a year.
An exemption was made for a cat living at his Benhar home.
The manager of the farm at the time, Murray John Illing was fined $2750 and ordered to pay vets' costs of $1851 for failing to protect the animals under his supervision.