As the next generation of the cow herd, raising replacement heifers to have healthy, productive lifespans is critical to cow-calf producers.
At a heifer selection and development workshop held at the University of Missouri Southwest Research Center recently, MU Extension state beef reproduction specialist Jordan Thomas gave tips on selecting heifers for longevity and performance based on prebreeding exams.
“In terms of prebreeding exams, what we’re really talking about is a prebreeding reproductive evaluation,” Thomas said, adding the recommendations he provides originate from the Show-Me-Select Replacement Heifer Program and are geared toward commercial operations.
In prebreeding exams, the SMS program requires heifers have a 150 square centimeter pelvic measurement at prebreeding.
“It’s not uncommon for heifers to fail that at prebreeding,” Thomas said, “and if they do, they can be remeasured one more time at their first preg check.” He explained heifers may fail because they haven’t begun to cycle yet so small measurements are not uncommon. However, when measured at preg check, heifers must meet a higher requirement of 180 square centimeters due to the growth they should have had since the prebreeding exam. Thomas did explain the numbers are a bit subjective because the measurements should take into account the mature size of the animal.
“It’s a little bit arbitrary but it’s a really good, safe point to be across a lot of different breed compositions,” he said.
The prebreeding exam, Thomas explained, should be done typically 30 to 60 days before breeding and include a reproductive tract score and prebreeding booster vaccinations. This can also be done in a timely manner with an estrus synchronization program like a 14-day CIDR protocol.
Reproductive tract scoring involves the palpation of the uterine horns and ovaries and is given on a scale of one to five.
“We’re really trying to feel the ovaries and palpate the structures that are present on the ovaries,” Thomas said, explaining a score of one is a heifer that is prepubertal with no palpable follicles on the ovaries.
“When you palpate that, it’s often kind of like cooked spaghetti in terms of the size of uterine horns — we’re talking really small, infantile tract,” he said.
A score of two is a bit larger but still more than 30 days away from initiating her first pubertal estrus. Threes have a fairly well-developed tract but the ovarian structures indicating the heifer is truly cycling are not present. However, a three should be within 30 days of her first pubertal estrus. A heifer with a score of four or five is cyclic. The difference is the presence of a corpus luteum on the ovary, indicating she is in the luteal phase, in a heifer with a five score. A four-scored heifer’s ovarian structure would indicate she is in the follicular phase of her cycle.
“It’s not an arbitrary, sort-of-subjective classification of heifers — it really has to do with real hormonal changes that are happening around the time of puberty,” Thomas said.
“It’s a really good predictor of things like pregnancy rate to fixed-time AI. It’s a really good thing for pregnancy rate by day of the breeding season, so those higher tract score animals are becoming pregnant earlier, even just in a natural-service system.”
Because heifers with higher tract scores are becoming pregnant earlier on average, producers can also use this to predict they’ll wean heavier weight calves.
“Our recommendation is, for sure, cull those tract score one heifers — remove them from your breeding program in general,” Thomas said. Twos and threes, he added, are a judgment call, depending on the specifics of the heifer and the operation.
“Threes are going to do quite well in a lot of cases on progesterone-based protocols,” he said. “If you’re not using a protocol like that, I get a little more concerned about these twos and threes.” Heifers with tract scores of four and five are both cycling so he said both do well in a fixed-time AI program.
Prebreeding exams also allow producers to evaluate their heifer development programs.
“If you’re not hitting 50 percent fours and fives, then it’s time to go through and troubleshoot and figure out why,” he said, adding some explanations may include heifers being limited by nutrition, age variation, parasites, sire group differences, etc.
“This prebreeding evaluation is a really good tool because it gives you some really good information to make a direct assessment of puberty status… a direct assessment of reproductive maturity,” Thomas said.
Thomas also suggested using data and records in the heifer selection process.
“Everybody can do this tomorrow and it doesn’t cost you any money, and that’s just a tremendous opportunity to keep and analyze records,” he explained. “If you can do that, obviously it makes you more profitable for a couple of reasons: It can increase revenue, it can cut costs, and it can increase the rate of return on assets — this is really the best metric we ought to think about.
“If we could, we wouldn’t run cow-calf enterprises the way we actually do today,” he continued. “If we could, we would know a profit and loss on an individual cow, and we would cull our lowest performing cows from a profitability standpoint… and we would select for cows that are more profitable.”
Thomas explained knowing the revenue of each animal is pretty simple but tracking costs, such as grazing costs, to individual animals can be more difficult.
“We’re looking at profitability indirectly using animal performance that research has shown is associated with profit or indicators of potential performance,” Thomas said, adding criteria a heifer must meet to potentially be profitable include being born early in the calving season. According to data out of Nebraska, heifers born early will raise 1.2 calves more over their lifetimes than heifers born late in the calving season. Heifers born early in the calving season also tend to have more longevity in the cow herd.
“Not only do you get more calves out of those early-born heifers, you get heavier calves out of those early-born heifers because they conceive early so they calve earlier,” he explained.
Another item to consider is a cow that conceives on the last day of the breeding season and calves on the last day of the calving season is far more likely to not be cycling at the start of the next breeding season, Thomas said.
“She may not even be cycling at all during the breeding season depending on several factors — if she’s in poor body condition or low plane nutrition, etc.,” he said. “She’s going to have fewer opportunities to become pregnant that breeding season and a higher rate of fall out.”
He also reminded producers that genetics aren’t everything when it comes to performance — environment has its role.
“Sometimes when we talk about genetics, we talk about phenotype equals genotype plus environment,” he explained. “I’m going to tell you that in a commercial context you kind of get paid on phenotype, so genotype really matters to the extent that it affects phenotype.”
Heifer genetics do matter because they affect performance but her performance is also influenced by environment — not just temperature and humidity but the entire management system.
“You need to select for both of those things as a commercial producer because you get paid on their performance,” he emphasized.
Thomas reminded producers of the top three revenue drivers in commercial cow-calf operations:
1. The number of calves a cow weans over her lifetime.
2. The age and weight of calves at weaning.
3. The quality of calves weaned.
Both No. 1 and No. 2, Thomas said, are related to early and late conception and should be considered in the selection process. He also recommended producers consider the job description of heifers, culling unsound heifers and considering birth date over size because “cow size has gotten too big for our forage base.”