Scientists have for the first time identified the most food-efficient dairy cows.
Industry body Dairy NZ, working with Australian researchers and genetics and breeding company Livestock Improvement, has just completed a six-year project studying about 2000 calves.
The Feed Conversion Efficiency Programme was carried out at a customised feeding facility in Hawera in Taranaki and a similar one in Victoria, Australia.
Dairy NZ chief scientist Eric Hillerton says researchers found a 22% difference in feed eaten by calves to achieve the same weight.
The most efficient 10% and the least efficient 10% of the calves were then grown on and tested to see whether they were still different by the time they were producing milk.
Mr Hillerton said the more efficient ones produced the same amount of milk for less feed.
Livestock Improvement found genetic markers underlying the differences and will say in this season's catalogue which bulls whose semen they are selling carry the genetic trait.
He said farmers will be able to use the findings so they can choose and breed the most efficient cows for milk production.