VICTORIAN research shows that artificially inseminated-bred cows are an average $53 a year more profitable than their naturally bred counterparts.

That equates to an extra $21,000 profit every year for a 400-cow herd.

Victorian Department of Primary Industries researchers Mekonnen Haile-Mariam and Mike Goddard used milk price, input costs, production and lifespan figures from the national herd recording data to quantify the value of AI to a dairy farm.

It is the first time the widely held view that AI cattle increase profit has been backed up by figures.

The research from about 270,000 AI cows and about 30,000 non-AI cows showed the lifetime net income for an AI cow was an average $195 more than a non-AI cow, AI cows produced an average of 138 litres more milk and remain in the herd almost two months longer.

Mr Haile-Mariam said AI cows were more profitable because they produced more milk solids and more lactations.

The difference in calving interval and age at calving also favoured AI cows, he said.

"More frequently calving cows are more efficient than cows with longer calving intervals," he said.

"While we used 2000 costs and prices to calculate income and cost, the outcome would be similar using today's costs and prices."

Mr Goddard said with AI cows productive for longer, farmers had to cull fewer cows.

"That longer life works out to be equivalent to having one to two cows for every 100 that a farmers doesn't have to cull," he said. "Not having enough AI heifers to use as replacements means they miss out on a bit."

Michelle Axford, of the Australian Dairy Herd Improvement Scheme, said genetics was the reason AI-bred cows were more profitable.

"It's not the practice of AI itself; AI sires are selected for their genetic ability to contribute higher profit from efficient production, longer survival and improved fertility," she said.

"Sometimes when it gets really busy on the farm at this time of year, it is tempting to put in a mop-up bull to save time, but don't be too hasty.

"Continuing AI for an extra week or two should mean more AI heifers for replacements, to expand the herd or increase income by selling the surplus."