For cow-calf producers, it’s impossible to determine which of their heifers will become their most profitable long-term females simply by eyeballing them over the fence. While their outer makeup displays part of the puzzle, it’s on the inside where much of the crucial decision-making information lies.
“Completing a phenotypic evaluation is a routine part of selecting heifers,” says Jordan Thomas, assistant professor in the University of Missouri’s Division of Animal Sciences. “It’s important, as we want to rule some out for non-reproductive issues such as structural soundness, poor eyes and obvious health concerns, but there should be more to our selection decisions.”
Thomas says after a visual assessment is complete, a pre-breeding (PB) examination, including reproductive tract scoring (RTS) and pelvic measurements (PMs), is an excellent way to complete a bigger portion of the puzzle. He recommends these exams occur at least 30 days before breeding, as this is when operations using an estrus synchronization protocol would begin their program.
“A commonly used 14-day CIDR-PG protocol is 33 days long,” says Thomas. “The pre-breeding exam could be done on the same day CIDRs are placed. It’s also a convenient time to complete any pre-breeding boosters and vaccinations.”
Thomas explains 30 days also provides enough time to make nutritional modifications regarding current weights in relation to mature weights, but warns that, if completed too early, PMs will identify too many smaller pelvises, as heifers aren’t mature and RTS will indicate most haven’t reached puberty. Waiting until closer to breeding offers more actionable information.
Balancing frame size using pelvic measurements
The earliest PB exams began strictly as pelvic measurements to screen out animals with abnormally small pelvises. Thomas believes they’re still a worthwhile place to begin with many programs. PMs are simply a measurement of the birth canal area in relation to the size of an easily deliverable calf. Results are determined using a pelvimeter, a caliper-type instrument that measures the vertical and horizontal opening. Measurements are multiplied to calculate a total area.
He says while some producers use PMs to measure for larger size and growth, he discourages this train of thought as an incorrect use of the tool. When only females with the largest pelvises are intentionally retained, an increase in overall size throughout the herd will result, which isn’t normally the desired goal.
During a recent beef cattle extension service presentation, David Christiansen, DVM and assistant professor in Mississippie State University’s Department of Pathobiology and Population Medicine, discussed pre-breeding exams and outlined the importance of comparing pelvic measurements to heifer size.
“By simply culling those with smaller measurements, we’re automatically selecting for larger frames,” he says. “It shouldn’t be about only removing the smallest but also taking into account age and eventual frame-size projections.”
Christiansen also emphasizes the need to look beyond the overall measurement and account for shape. He says tall and narrow or short and wide presentations are an indication of potential calving difficulty.
Reproductive tract scoring: Culling or selecting?
During a 2021 Cow-Calf Corner presentation, Oklahoma State University Extension reproduction physiologist Daniel Stein discussed the specifics and benefits of RTS on potential replacements.
“RTS is a subjective management and selection tool evaluating the maturity of the reproductive tract using a 1 to 5 score,” he says. “The cost of keeping females is part of financial efficiency, and if an RTS is done early – before breeding season – we can tighten up our calving interval and market those that don’t qualify.”
Using rectal palpation of the tract, including the uterine horns and ovarian structures, a 1 through 5 score is assigned as a measurement of pubertal status (Table 1).
Stein recommends RTS be completed about one month prior to breeding if used as a culling tool when a heifer’s ability to conceive early during the first breeding season is desired. When used as a selection tool to place pressure on age at puberty, he proposes waiting until approximately 50% are thought to be cycling based on age, weight and heat detection observations.
Adding tools to traditional thinking
Thomas reinforces the goal of selecting heifers with the strongest chance of return on investment as profitable cows. He says data indicates those calving early in the season have a head start on reaching this target.
“I advise not thinking about heifers as replacements until pregnancy diagnosis,” he says. “In a perfect world, only those conceiving early in the breeding season should stay in the herd.”
Thomas admits that for this to occur, more heifers than required need to be bred to develop enough early conceiving females. Alongside RTS and PMs, Thomas suggests genomic testing could be incorporated into the selection process by testing early conceiving animals for desirable traits.
“Packaged together, this information would screen out females not likely to conceive early using a pre-breeding exam; then at preg checking, determine the most profitable pool of commercial females to keep. Additionally, genetic testing could be used to select for the best of the best.”
Thomas believes it would be beneficial for more producers to use at least a portion of pre-breeding elements, as feed costs and breeding expenses add up quickly. Proactively recognizing and marketing unsuitable heifers as feeders rather than carrying them for months only to confirm them open is ideal.
“The largest opportunities take shape when components of pre-breeding exams pay for themselves,” he says. “This manifests in our ability to remove heifers that otherwise would have incurred unwarranted expenses. Pelvic measurements, phenotypic evaluations and reproductive tract scoring are all excellent tools to help us identify and remove these poor candidates from the equation.”
