Mousel, speaking to producers at the Applied Reproductive Strategies in Beef Cattle conference on Dec. 3, showed South Dakota data and USDA studies affirming what most cattlemen have seen up close. Heifers that calved early in the season saw increased longevity, productivity and even more profitability over their lifetimes.

“Identifying the heifers that calve early in the calving season could potentially be the simplest method to improve longevity and probability in any herd, especially commercial herds,” Mousel said.

Every ranch has its own management style, which means those kinds of results vary from herd to herd. But the basic principle holds true that selecting heifers based on early conception and early calving shows connections to longevity in the herd.

The temptation for many producers when selecting heifers for fertility may be to opt for phenotypic traits. Many cow-calf operators choose for size – with an eye for the “growthier and soggier” females, Mousel said, in addition to maternal performance from the dam, or what sire the heifer is from.

But it’s actually difficult to phenotypically analyze heifers for fertility, Mousel said, and there’s little heritability associated with most fertility.


“Just because mama was a pretty fertile cow does not guarantee that the daughter is.

 “The tendency of cc producers is to select those oldest and largest heifers as a proxy for fertility. Any cattleman can tell you, a lot of those are some of your most fertile females. But it’s not all of them. Some of the best-looking heifers, when you pick them out, can be the latest breeders. And some of the most scraggly-looking females can be some of the most fertile.

“As we look at this, we have to recognize that breeding fertility at a population level probably is not that achievable.”

Instead, the selection for fertility and longevity requires more direct ties to conception and early calving.

Mousel outlined two data sets – one from a small group of 2,200 heifers from South Dakota producers, another from the U.S. Meat Animal Research Center using 16,000 heifer records over 20 years. The heifers were sorted into those charted on 21-day cycles. Open females were removed from the study.

“We definitely saw that heifers that calved with their first calf in the first 21-day period had increased longevity over the course of their lives, compared to those that calved in the second or third periods,” Mousel said.

Records from the USMARC research showed 65 percent of the females that calved first remained in the herd up to 10 years. About 54.7 percent were left after 10 seasons when they were second-cycle breeders and second-cycle calvers. The South Dakota data saw a steeper drop-off. Only 14.3 percent of first-cycle heifers remained after 10 calving seasons. The biggest drop of females out of the herd came after their third calf.

Mousel said of the USMARC heifers, those that calved first in the first 21 days had an average longevity of 8.2 years. The second-period calvers averaged 7.6 years.

In the South Dakota data, the first-period breeding and calving heifers saw average production periods of 5.1 years, compared to 3.9 years to second-period heifers.

But Mousel said the differences between the state and U.S. studies isn’t the key, but “what is important is the difference between the first cycle and the second cycle (in both studies). Not only does that show us there is a positive relationship (between periods of calving), but it shows us it can be variable in different herds.”

Mousel said the ability to get a heifer synched to an early start pays off years down the road. A heifer needs to deliver and raise six calves before she pays off all the production put into her development. Everything after that is profit.

“Females that have longer reproductive lives, not only are they going to wean more calves, and thus have the potential for higher lifetime weaning weights, and weaning weight averages, they’re also going to produce more calves.

“There will be real advantages for these females to stick around in the herd longer.” end mark