Breeding heifers to calve in around 2 years old puts them on a productive track to begin paying off the costs of their rearing and avoid mounting up additional expenses while they remain open. Calving age is also a balancing act, though, because when animals start their productive life before they are mature enough to do so, it can sacrifice future performance.

Reduced milk production, more disease, and greater culling are all correlated with animals that enter the milking herd at less than 85% of mature bodyweight, said Iowa State University’s Larry Tranel. Gavin Staley, BVSc., a veterinarian with Diamond V, considers these to be “Peter Pan” heifers — they haven’t yet grown up, and once they are milking, the development they should have experienced can’t be made up.

“They’ll try to grow, but it’s going to be at the expense of lactation,” said Tranel on a Dairy News and Views podcast. Sharing a presentation developed by Staley, he cited that it is seven to eight times more inefficient for animals to work toward reaching that bodyweight threshold after calving than before.

It might seem most cost-effective to get heifers into the milking herd as soon as possible, but the effects of this stunted development mean that those animals likely won’t stick around in the herd as long. Tranel said a cow usually doesn’t pay off its rearing cost until sometime in its second lactation. To make the most out of the genetic and management investment a farm is making for each animal, three lactations and beyond are the most desirable. Early calving heifers are less likely to reach this age.

Heifer development varies by farm but calving at 21 or 22 months might be considered early. To gauge how your first-lactation animals are doing, Tranel advised monitoring production of these animals at Week 10. This number will approximate your annual daily herd average, he said.