Helen Meads had made up her mind it was time to move on.

After 10 years of marriage to a Matamata horse breeder with whom she had a daughter and a successful stud farm, Mrs Meads told her husband she was leaving and looking forward to a fresh start.

But within days of hearing the news, her husband, upset by text messages he had read on her phone, confronted her in a barn and shot her in the throat.

Yesterday, horse-breeding identity Gregory Howard Meads, 55, appeared in the High Court at Hamilton charged with the murder of Mrs Meads at their Matamata home on September 23 last year.

The court heard that the 42-year-old Mrs Meads told her husband four days before her death that she wanted to move out of their home and move on with her life.

Addressing a jury of eight men and four women, Crown prosecutor Ross Douch said Meads began checking his wife's text messages on her phone, forwarding more than 100 of them to his own cellphone and then to his computer while she was asleep.

Mr Douch said some of the texts could be "construed as not complimentary" towards Greg Meads.

"They included a text from a friend who said, 'Make sure you clean the house out. Just leave him with his clothes in a pile on the floor'."

The next day, Meads took his step-daughter Kimberley, 18, and his daughter from his marriage to Mrs Meads, 10-year-old Samantha, to school.

Mr Douch said Meads was gripped by "fear, bitterness, anger and rage" when he walked into a stable where his wife was on her mobile phone talking to a friend.

He said Meads would later tell a detective that he took the firearm to "give her a fright".

"I'd give her what she's giving me," he told the detective.

"I was walking around and it was going through my mind that this is the people she has probably arranged to clean my house out.

"She finished on the phone, I picked up the gun and shot her."

In his opening address, defence lawyer Murray McKechnie said his client had made "the most appalling decision of his life".

But he had never intended to kill his wife.

Mr McKechnie, who is seeking a manslaughter conviction for his client, said Meads was highly stressed over their break-up and had not slept for days.

"If he had intended to kill her when he got to the stables, I suggest he would have just walked in there and gone 'bang'," he said.

"Our position is he did not intend the gun to go off, he did not take aim at her, he did not go there to kill her.

"This shooting was unlawful, as the Crown solicitor has rightly said, and because it's an unlawful shooting it's a manslaughter."

Meads, who sat impassively and calmly through yesterday's evidence a few metres in front of his wife's distraught family, is a successful figure in the horse-racing industry.

He and his former wife were partners in the Willow Park Stud and had been in business together, breeding and training horses, since they were married.

Among the racehorses they owned were Kristov, Wolf Pack and the top-performing Ginga Dude, in which Meads last year sold his stake.

The trial is expected to run until early next week.

THE CROWN

Wants a murder conviction against prominent horse breeder Gregory Howard Meads for shooting his wife, mother of three Helen Meads, 42, at their Matamata home on September 23 last year.

THE DEFENCE

Wants a manslaughter conviction. Says Meads, 55, wanted to talk to his wife, and never intended to kill her when he went to the stable carrying a shotgun.