Twenty-one witnesses will give evidence over the three to four-day trial, which will include a site visit tomorrow.
Mr Dew told the court yesterday he spent three days examining the herd, many of which were so badly emaciated they could not get to their feet and had to be euthanised on the spot.
Many were well below the acceptable body size, which indicated to him poor animal management, prolonged neglect and underfeeding.
One animal he had to euthanise was located near the farmhouse.
Mr Dew said he could not comprehend how that animal had not been seen and put out of its misery earlier.
"I was shocked. Many of the animals weighed between 150kg and 210kg -- they should have weighed between 380kg and 480kg."
Healthy cows should have a body conditioning score (BCS) of six or more; those on Ham's farm scored less than three and some as low as 1.5. "This could only happen through gross mismanagement and underfeeding for a long time," he said.
He noticed there was very little pasture and what pasture there was, was of a poor quality.
"There were also multiple dead animals in drains."
Opening for MPI, lawyer Kathy Bell said Ham had leased his farm in July 2010 to Jeremy Usher, including 600 dairy cattle. In 2012 Usher travelled overseas and his father Robert ran the property.
A ministry inspection in late August 2012 found the farm was overstocked and the animals had been neglected, Ms Bell said.
"Of the 926 cows on the property, 634 had to be physically examined and from that 152 euthanised and another 128 had to be sent for slaughter, because of their poor condition."
While Ham had leased out the running of the property, he was still living on the farm and still had an input and involvement with the farm.
She said the ministry firstly had to prove to the court that Ham owned or was in charge of the animals, and for the second charge of ill-treatment the issue was whether Ham himself had ill-treated the animals.
She said the ministry submitted that by way of omission, Ham should have taken action and his failure to do so had resulted in the ill-treatment. He was aware of the ill-treatment.
"There was evidence also of Ham's continued and ongoing involvement in the farm, although the extent would be an issue. He did retain ownership of the 600 stock he leased," Ms Bell said.
The Ushers had moved more stock on to the property, some of which were progeny of farm stock.
"The defendant agreed with Robert Usher to allow extra cattle on to the property, and before July 2012, 109 new cows were taken on to Ham's property and they belonged to Robert Usher's daughter, Amanda," Ms Bell said.
