Summer-born heifers developed to breed as yearlings the following fall had normal yearling pregnancy rates, but had low rebreeding rates as 2-year-old cows. That’s according to three years of research at the University of Nebraska’s Gudmundsen Sandhills Laboratory. Led by Gene Seutscher, professor emeritus of animal science at the University of Nebraska, the researchers studied 240 spring-born and 146 summer-born heifer calves. The replacement heifers where selected for high weaning weight and moderate birth weight.

“The results on the summer-born heifers are of particular interest to ranchers who are summer calving or are considering moving their calving season to summer,” says Brent Plugge, NU Cooperative Extension educator for the Central Sandhills Area, who assisted with the research. “Those producers need more information on heifer reproduction and nutrition so they can mange the young cows efficiently in a summer calving herd.”

Rebreeding rates for 2-year-old summer-born cows were 77 percent over two years compared to 90 percent over two years for the spring-born cows.

“About 35 percent of the summer heifers were culled due to reproductive failure before they were three years old,” says Dr. Deutscher. “These rebreeding rates where unsatisfactory.”

Researchers are now examining ways to increase second-calf pregnancy rates in summer-born females. If you herd calves in summer, be sure to keep tabs on reproduction performance of those and all replacement heifers.