Properly developed and managed beef heifers generally have a 20- to 30-day longer postpartum interval than older cows.

"The practice of breeding virgin heifers 20 to 30 days earlier than the cow herd will allow the heifer additional time to return to estrus and rebreed with the older cows the next year," says Rick Funston, extension beef specialist at Montana State University.

It is important to manage these heifers separately for two reasons explains Mr. Funston. First, earlier calving will likely mean that pastures are not available as soon and additional nutrients will need to be supplied. Second, nutrient requirements are higher for first-calf heifers than they are for mature cows. Breeding heifers early will be of no benefit if they are not properly managed after calving.