Skip to Content

The Weekly News Source for Wyoming's Ranchers, Farmers and AgriBusiness Community

Larson looks at early breed-up as top priority

by Wyoming Livestock Roundup

Gillette – Bob Larson of Kansas State University has focused on the cowherd in his research over many years, and he says, “One of the things I feel is most important is to get cows pregnant and get them pregnant early in a controlled breeding season of 70 days or less.”

When cows – and heifers – get pregnant early, Larson says they are more successful and more likely to breed up in future years.

“I want my herd to be front-end loaded during the calving season,” he adds. “What that means is that I want a lot of the cows to calve early. I want two-thirds in the first 21 days.”

Larson presented to a group of producers in Gillette on March 3 at a presentation sponsored by Boehringer Ingelheim. He also presented in Sheridan and Sundance the same week.


Larson says that during breeding, there is a two-thirds chance of getting a calf if a fertile bull and a fertile cows are mated once in a 21-day period.

“About one-third of the time fertilization fails or there is an early embryo that doesn’t make it,” he explains. “That is the complexity of beings like cattle, and I don’t think we will be able to change the complexity that is starting a new life.”

Another thing to keep in mind is the period of infertility that comes after a cow calves.

“The period of infertility following calving lasts about 60 days when cows are in decent body condition,” Larson says. “If she is thin, it is increased 10 days to two weeks for every body condition score before five that she is.”

That 10 to 14 days makes a big differences, he adds, in future calving season, and the infertile period is longer for first-calf heifers.

“For those first-calf heifers, we are talking about 90 days before she resumes fertile cycles,” he says. “This is a problem we’ll focus on.”

The post-partum infertile period is a major reason that early calving is important.

“The best I can hope for is if cows are fertile and cycling,” he adds.


“If cows are fertile and cycling, they could get pregnant in the first 21 days if bulls are doing a good job,” Larson explains. “The best in that scenario is that two-thirds will have a calf in the first 21 days of the calving season.”

Two-thirds of the cows that don’t settle to the first mating will get pregnant in the second 21 days period. Two-thirds of the remaining herd gets pregnant in the third 21-day period, leaving approximately five percent of the cows open.

“If I have a 63-day breeding season, the best I can hope for is 95 percent pregnant,” he says.

The longer it takes cows to get pregnant, the more likely they will breed up late the following year, Larson explains, adding that the number of days in a year, coupled with the days of gestation and infertile period means that timelines, particularly for heifers, are tight.

“The heifers that don’t get pregnant in the second year are the ones that didn’t get back into heat in time,” he says.

Breaking down the numbers, Larson explains that 283 days gestation, plus a 90 day post-partum period adds up to 373 days. Followed by a 21-day breeding season, it’s a push to get heifers back into breeding shape.

Value of calves

In addition to seeing good breed-up, calving early adds additional pounds to calves, Larson notes that it also increases the weight of calves by sale dates.

“If I have a 300-head herd that calves March 1 and we wean Nov. 1, our calves will be 500 pounds if they gain 2.2 pounds per day,” he says. “If 500-pound calves sell for $1.95 next fall, we can see more profit from the heavier calves born early.”

The cattle are from the same genetic background, so they should perform consistently, Larson says, noting that the extra weight from a group that calves early sees an increased income of over $90 per calf in a herd with a three-month calving window compared to a five month window.

“We see $12,000 for a 300-head herd of increased profits,” he comments. “No one sends us a bill for the lost profits, so they’re invisible, but it still matters.”

Larson adds, “We are comparing the good herds with the very best herds. We can’t see the difference, but the best herds make more money.”

Heifers first

The increased post-partum interval also means that heifers must calve before the cows.

“On average, our heifers will calve two to three weeks later than they calved last year,” Larson says. “That drops them back to the end of the season for the next year.”

The only way to maintain a consistent, early-calving herd is to calve the heifers first.

“The only way to make it work so we get a flat pattern in our calving is for our heifers to calve ahead of the cows,” Larson comments. “It might not be ideal, but with a 90-day period of infertility, if I want them to be front-end loaded, I want heifers first.”

Additionally, Larson also mentions that calving heifers first also puts the majority of the labor at the front of the calving season.

“Heifers are the biggest part of my calving difficulty,” he says. “If I have 30 to 40 days of heifers and two-thirds of my cows over the next 21 days, I’m almost done with the work in 60 days.”

Saige Albert is managing editor of the Wyoming Livestock Roundup and can be reached at

Back to top