No more than 18% of your dairy herd should be made up of replacements, unless you are expanding, Doreen Corridan said at an Irish Feed and Grain (IGFA) conference last Thursday.

It is mature cows that will drive production and “belt out” milk solids, she said, with heifers producing 22% less milk than third-lactation cows.

“If you look at a lot of herds, and you look at their co-op report, if the fat and protein kilos are low, the first thing I look at is the breakdown of the herd.

“If there are too many first calvers in any herd, they will not end up with a high overall production. It’s the mature cows that drive production. The difference between the herd that’s producing and a herd that’s not producing is the genetics and the maturity of the herd,” she said.

Corridan added that 60% of the herd should be third lactation-plus cows. Mature cows are also better able to breed a better beef calf, she added.