Martha Blum, Field Editor
DUBUQUE, Iowa — Replacement heifer selection begins when sires are chosen for the cowherd.
“Eighty-five percent of the genetic makeup of cowherds is contributed to sire selection,” said G. Allen Bridges, assistant professor at University of Minnesota.
“Select the right sires to produce the right females,” said Bridges during a presentation at the Driftless Region Beef Conference, sponsored by Iowa State University Extension and Outreach, University of Illinois Extension, University of Minnesota Extension and University of Wisconsin Extension.
“Don’t discount dam selection because it is critical,” he added. “But it gets ignored in a lot of our commercial operations because we breed every female.”
Cattlemen have selected for genetics for a long time.
“Researchers have noticed what a heifer calf is exposed to during gestation or early life can effect what genes are expressed,” the specialist said. “It doesn’t change the DNA code, but it can change what genes are expressed.”
Research work at the University of Nebraska evaluated the impact of protein feeding during gestation on the fertility of heifer calves.
“If you restrict the protein of a pregnant cow during the second and third trimester of gestation, the heifer calf she produces won’t be as fertile as the heifer that had adequate protein during gestation,” Bridges reported.
“We’re still trying to learn, but in the next few years, I think you’ll see some pretty interesting data on how we can influence future productivity of cows by how we feed their mothers,” he said.
Cattlemen need to match genetics with their environment.
“We have to make sure we’re balancing both,” the specialist explained. “We could have the best genetics in the world and if we don’t feed the animal right or make sure the animal stays healthy, that genetic potential goes down the drain in a hurry.”
Using EPDs, expected progeny differences, is important to make selections for both sires and dams.
“Prioritize the traits of economic importance to your herd because we have a lot of EPDs to choose from,” the professor said. “And match traits to your environment.”
For example, in Minnesota, Bridges said, there is not a lot of corn grown.
“We ask our cows to make it through most of the year on grass,” he said. “I can’t afford to have more than 35 milk cows because I can’t feed them.”
Cattlemen should avoid selecting for a single trait.
“Pick traits that are important to you and be balanced,” Bridges advised.
He identified several goals for heifer development.
“Heifers need to reach puberty by 12 to 13 months of age,” he said. “And the No.1 thing that influences puberty is nutrition.”
“We want them to have multiple estrus cycles before they are 15 months of age,” he explained. “The more estrus cycles they have before breeding them, the more fertile they are to that first breeding so they calve by 2 years old.”
Other goals include minimal assistance at calving, rebreeding as 2 year olds and a target weight of 65-percent mature body weight at breeding time.
“Retain heifers with the heaviest actual weaning weight because they’re the cheapest to feed to hit the target weight,” the specialist said. “And retain more heifers than you need because about 10 percent of the heifers you keep will never get pregnant for various reasons.”
If there is a lot of variation in the weaning weights of heifers, Bridges said, cattlemen may want to split feed them.
“By feeding two groups, it will be easier to hit targets and more economical in the long run because you feed the heavy heifers less,” he said.
Bridges provided data on research that was completed at the U.S. Meat Animal Research Center in Nebraska. The data included 16,000 heifers, and the researchers focused on first calving and longevity in the herd.
“If the heifer calved within the first 22 days of the calving season, she stayed in the herd longer than those that calved between day 23 to 42 or those that calved after day 43,” the professor said. “Those heifers that were bred early and calved early stayed in the herd longer.”
In addition, Bridges reported, heifers that calved in the first 21 days of the calving season had greater calving weights through their fifth calf compared to the other two groups.
A study completed in South Dakota looked at the impact of moving heifers from feedlots onto pastures. The heifers were developed in a feedlot and then put out on grass the day after the heifers were bred by AI.
“In the feedlot, the heifers walked about 1 mile per day, and the first two days on grass those heifers walked 4.5 miles per day,” Bridges said. “The heifers were not use to eating green grass, because they had been eating out of a bunk.”
In another similar study in South Dakota, heifers were again developed in the feedlot and then put on pasture.
“The first week after hitting the range, the heifers lost over 3.5 pounds per day,” the specialist said. “Those heifers were looking for food, and they were looking for a bunk.”
Bridges stressed the importance for cattlemen to focus on the proper development of heifers for their herds.
“If we don’t development them right, get them to puberty and bred early, the heifers don’t stay in the herd as long or produce as heavy calves,” he said.