In anger, he turned the handpiece over and hit the lamb twice in the right eye with the protruding tension knob.
This fractured the lamb's eye socket and caused fragments of the orbital bone to go into the lamb's eye.
Tredinnick then put the lamb back into the holding pen behind him.
Shortly after he went into the pen taking his handpiece with him and hit the lamb again.
This caused a serious skull fracture with multiple fracture lines and a piece of bone 3cm in diameter was dislodged into the skull.
He then pulled the lamb out of the holding pen, still alive but "limp and unresponsive" and shore it before pushing it down the chute where it later died of its injuries.
When he finished work he took the lamb's body from the bottom of the chute and put it in his vehicle.
When questioned by the farmer he told him the lamb had suffocated and he would take it home to feed his dog.
On February 21, MPI animal welfare inspectors searched Tredinnick's address and recovered the lamb's remains which were taken for a postmortem to a veterinarian, who concluded the lamb had died of two "distinct episodes of blunt force trauma" resulting in the fractures.
The veterinarian said the lamb would have been in extreme pain and distress and the injuries caused its death.
When spoken to by MPI, Tredinnick declined a formal interview, said the incident never happened and the allegations were "bull...".
Judge Turner also read other evidence.
In February, the Society for the Prevention of Cruelty to Animals issued Tredinnick with a letter regarding physical ill-treatment of his pet German shepherd.
MPI prosecutor Lisa Brown had earlier submitted jail was appropriate but acknowledged home detention was likely.
Tredinnick was "not a man who should be working with animals", she said.
She also sought a disqualification period of no less than four years in relation to all animals.
Counsel for Tredinnick, Kieran Tohill, said his client "lost reason" but it was a "one-off" and Tredinnick had shorn hundreds of thousands of sheep in his shearing career.
He submitted a sentence of home detention but Judge Turner ruled this out as a suitable address had not been provided.
Judge Turner sentenced Tredinnick to 16 months' jail with leave to apply for home detention, disqualified him from owning or being in charge of an animal for two years, and ordered him to pay reparation of $454 to cover the veterinary bill.
MPI animal welfare national manager Gray Harrison said Tredinnick's actions were "appalling".
"He deliberately caused this lamb to suffer and he tried to hide that fact. Animals need and deserve to be treated with respect, and Mr Tredinnick fell well short of those expectations," Harrison said.
"This kind of offending by shearers is unusual. The majority are professional and do the right thing. However, our message for those who deliberately cause this kind of suffering is clear: we will investigate and place them before the court."
