by: Carla L. Huston, DVM, PhD ACVPM
Beef Extension and Outreach Coordinator, College of Veterinary Medicine, Mississippi State University

On average, 15-20 percent of the beef herd is replaced each year. Chances are, if you are raising your own females, you already have your eye on the next set of replacements. There are many tools available to help you choose which heifers to retain; for example, keeping heifers that were born early in the season and who have good milking mamas makes sense. But while many reproductive characteristics are highly heritable, we can't always judge a heifer's potential lifetime productivity based strictly on her dam.

Breeding soundness exams (BSEs) can be used to help you decide which females have the greatest potential for becoming productive members of the herd. Research has shown that heifers that conceive early during their first breeding will calve earlier and wean older, heavier calves than heifers that conceive later in the breeding season. Furthermore, heifers that conceive and calve early with their first calf tend to continue to conceive and calve early throughout their lives.

In heifers, BSE's should be performed 30-60 days prior to the breeding season. This is also a good time to administer pre-breeding vaccinations and perform a parasite evaluation. When BSE's are done at this time, culling of reproductively inefficient heifers can occur before a large amount of labor, management, and expense is invested into getting them bred. There are 3 main components of a heifer BSE: pelvic measurement, reproductive tract scoring, and physical evaluation.

Pelvic areas can be used to identify those heifers who have very small pelvises and are likely to require assistance at calving. Combined with proper bull selection, you can minimize the risk of calving difficulties in heifers. Measurements are important to perform because heifer size is not always correlated with pelvic area, and the larger, heavier heifers do not always have the largest pelvic area. Caution must also be taken not to select replacement heifers solely on large pelvic size, as this will likely result in an increased mature cow size.

Pelvic measurements are determined rectally using an instrument called a pelvimeter, and the area of the pelvis in cm2 is determined by multiplying the width by the height. Using guidelines by Duetscher et al, dividing the pelvic area by a ratio factor of 2.1 can be used to determine the size of calf the heifer should be able to deliver without assistance. For example, a 12-13 mo. old heifer weighing approximately 600 lb with a pelvic area of 140 cm2 should be able to deliver a 67 lb calf. The ratio increases to 2.7 for older heifers around 800 lb measured at pregnancy examination. If measurements aren't taken until pregnancy examination, heifers with smaller pelvic areas can be aborted and sold as feeders, or watched more closely for calving difficulty.

Reproductive tract scoring is a method of estimating the pubertal status of a heifer, as well as the genetic ability of her to breed early in the breeding season and conceive at an acceptable rate. Scoring is determined by rectal palpation of the uterus and ovaries within a contemporary group of heifers. Reproductive tract scores are from 1 to 5, with 1 being an immature uterus with small inactive ovaries, and 5 being a mature uterus with larger active ovaries. In general, a score of 4-5 indicates the heifer has reached puberty, a score of 3 is slightly pre-pubertal, and a score of 1-2 is immature and indicates that the heifer is not ready to be bred.

Similar to the BSE in the bull, heifers are also evaluated according physical attributes, such as conformation, body condition score (BCS), and udder score. Heifers should be bred at an average BCS of 6, and kept on a good plane of nutrition with proper mineral supplementation throughout pregnancy to minimize weight loss at calving. Temperament and docility are also extremely important characteristics to consider when evaluating heifers as replacements.

Remember, BSE's are not just for the bulls. Performing a BSE on your replacement heifers will help provide you with information you need to make informed replacement decisions based on science and economics, and help protect your financial and genetic investments. For more information on heifer management and having your heifers evaluated for breeding, contact your local veterinarian or Extension livestock specialist.

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