Mr McDonald has set up West Otago Alliance, The Ripple Effect, near Tapanui and secured a contract with Lion Nathan in Dunedin to take all the brewery's brewers' grain once it is used in the brewing of its beer.
Brewers' grain is a byproduct from the beer-making process and full of nutrients, Mr McDonald said.
The grain could be fed to farm animals, including dairy and beef cattle and pigs.
Mr McDonald takes tonnes of grain from the brewery each week.
"It's great for the dairy cows. It's high in crude protein," Mr McDonald said.
He was quick to see the benefit in securing a contract for the byproduct and this is his first year of operation.
"I just pursued the contract. There was an opening for me," he said.
Mr McDonald's farming background gave him an understanding of animals' nutrition needs and farmers' nutrition planning routines.
There is an increasing number of dairy cows in the South and all needed supplementary feeding, he said.
The feed was ideal for indoor dairy cattle.
Another advantage was the relatively low price of the supplementary feed.
"And it's a good recycling programme," Mr McDonald said.
The fledgling company has only three staff, including Mr McDonald. The firm has bought a truck and employed a driver. The supplementary feed is delivered to farmers.
"We do it all ourselves," Mr McDonald said.
He hoped to add another truck to the operation as orders increased.
The company picked up the brewers' grain five days a week from Dunedin.
The company already had between 15 and 20 clients and anticipated steady growth in clients wanting the product.
"It puts weight on stock. It's good for beefing up," Mr McDonald said.
Company administrator Teena Haslemore said once pig farmers had fed the product to their animals they were very keen to continue.
The supplement was also good for putting condition on cows after calving, Ms Haslemore said. - The Ensign