The optimal calving age for dairy replacement heifers is 23 months, according to Professor Jud Heinrichs, from Penn State University.

Speaking at this week’s Alltech annual symposium in Kentucky he said targeting 23 months at first calving is more than feasible.

“This means breeding heifers at between 13 and 14 months of age, when they are at 55% of their mature bodyweight. These animals should be calved down at between 85% and 90% of their mature bodyweight.

“I no longer refer to absolute bodyweight figures. Rather, the focus must be placed on the percentage of animals’ final bodyweights. In practical terms this will entail farmers actually measuring the bodyweights of their mature cows and then using this as the benchmark target for their own specific heifer rearing programmes.”

Heinrichs’ research is pointing to daily growth rates of between 800 and 900 grams per day as being optimal for heifers.

“There is evidence to show that pushing heifers beyond growth rates of 1kg per day will impact negatively on subsequent milk yields,” he said.

“Our latest research trials confirm that each one month reduction in age at first calving will reduce heifer rearing costs by 5%.  This is a very significant figure.

Hindrichs said heifer rearing is the second largest cost on every dairy farm.

“Accelerated growth rates can be achieved on the basis of laying down age-related weight targets, which reflect the genetics of the breeding stock on individual farms.  This will entail farmers weighing their youngstock at regular intervals.

“In achieving this target milk producers will save considerably by reducing the length of time it takes a heifer to join the milking group. And of course, these animals will be producing a cash flow for the business that much earlier,” he said.