GRAPHIC CONTENT: Cows were beaten, had their tails broken and were shot in the kneecaps on a West Coast farm under the management of a farmer facing a likely jail sentence.

Michael James Whitelock pleaded guilty in Greymouth District Court on Monday to 12 charges, including ill treatment of animals, unlawful possession of firearms and attempting to pervert the course of justice.

He was bailed to his home in Timaru until sentencing on October 7.

Whitelock was the dairy manager for a Landcorp farm near Westport from July 2012 until his suspension in September 2013. A Ministry for Primary Industries (MPI) investigation began that month after a Landcorp manager arranged for a vet to examine the herd.

Of the 1100 animals, 152 cows and 57 heifers had broken tails. The vet told investigators that he had never seen the number of animals with broken tails as he found at the Totara Dairy Unit on Cape Foulwind.

MPI said tail breaking was a process where tails were deliberately twisted to force cows into a milking shed. The pain is likened to that felt by a person having their fingers broken.

Investigators found the mistreatment of animals was widespread on the farm under Whitelock's management.

One cow due to be euthanised was walked to the offal pit where Whitelock gave a single-barrel shotgun to an employee and instructed him to shoot the cow in the legs. Whitelock and three employees each fired one shot at the cow's legs before it was euthanised.

Some time in late July or early August 2013, Whitelock and farm assistant Cameron Hurst chased a cow, pulled her to the ground by her tail then proceeded to punch and kick the animal.

When the herd was being inspected, Whitelock tried to have the injured animal removed. The Landcorp manager later found the animal's body half buried in an area of bush on the farm.

Hurst was sentenced to community detention in January for his part in the cruelty.

MPI said Whitelock beat another cow with a fencing baton, which resulted in a traumatic eye injury. Whitelock then tried to euthanise the animal but failed and ended up putting her in the offal pit while she was still alive.

On a number of occasions, Whitelock apparently lost his temper after cows kicked off their milking cups. He knocked one cow over by sweeping her legs away and struck another on the legs with a kick bar so hard that he broke the bar. On another occasion he repeatedly punched a cow in the udder, which left her bleeding.

Whitelock instructed an employee to walk a cow with an injured hoof and possibly a broken leg two kilometres to the offal pit.

During the MPI investigation, Whitelock was also found in possession of firearms and ammunition despite not having a firearms licence. During a search of his Timaru property in December 2013, ammunition was found unsecured in Whitelock's children's bedroom.

He was also charged with attempting to pervert the course of justice by contacting witnesses to ask them to cover up for him and placing blame on other farm workers.

Judge Stephen O'Driscoll convicted Whitelock on all 12 charges and remanded him on bail until sentencing on October 7. He told Whitelock that granting him bail "should not be any indication of what the ultimate sentence will be".