More tools for selecting replacements for older heifers

Two key factors to a heifer being “successful” and remaining in the cowherd are 1) she becomes pregnant in the first breeding season and 2) she calves unassisted and rebreeds quickly.

By performing a breeding soundness exam (BSE) on heifers prior to breeding, producers can eliminate these factors as potential stumbling blocks and improve reproductive efficiency. A BSE of replacement heifers should include body weight, days of age, reproductive tract scores, and, if desired, pelvic area data.

The timing of a BSE will depend largely on nutrition, breeding and marketing plans for specific herds. By conducting the exam at least six weeks prior to breeding, producers have a chance to correct low body weights, but it offers less certainty about the percentage of heifers that are cycling at the start of the breeding season.

Performing the exams just prior to breeding gives greater certainty about the percentage of heifers that are cycling, but it doesn’t allow producers a chance to correct any potential weight issues.

Reproductive tract scoring is a method of evaluating reproductive tract maturity and cyclicity in pubertal heifers. In order to determine if a heifer is cycling, the reproductive tract is palpated to determine the presence of the corpus luterum or large follicles in the ovaries and to estimate the size of the uterus.

Based on these characteristics, heifers are assigned a reproductive tract score (RTS) of 1-5, with a higher RTS being more desirable.

Determining the RTS of heifers allows producers to select those that have good reproductive potential ,and cull others with poor reproductive potential. This evaluation also allows producers to identify and remove freemartins, immature heifers, heifers without a complete reproductive tract or any heifers that are already pregnant.

Calving difficulty or dystocia increases calf death loss, cow mortality, labor, veterinary costs, delays the cow’s return to estrus and decreases rebreeding efficiency. It can also lead to decreased weaning weights due to breeding heifers and cows to calving ease low birth-weight bulls.

According to Gene H. Deutscher, University of Nebraska Extension Beef Specialist, calving difficulty results in an estimated economic loss of $750 million annually nationwide.

Since a major cause of dystocia is a disproportion between calf size at birth and cow pelvic area, by conducting a BSE on heifers and collecting pelvic measurement data, producers can reduce the occurrence of dystocia in their herds.

Pelvic area is measured in square centimeters (cm2) by multiplying the width of the pelvis by the height of the pelvis. That number is then divided by a conversion factor, determined by heifer age and weight, to estimate the weight of a calf that a heifer should be able to deliver without difficulty.

For example, if estimating the deliverable calf birth weight of a 12-month-old that weighs 700 pounds:

  • Measured pelvic height = 14 cm
  • Measured pelvic width = 12 cm
  • Calculated pelvic area = 14 cm x 12 cm = 168 cm2
  • Conversion factor = 2.2
  • Estimated deliverable calf weight = 168 ÷ 2.2 = 76 pounds

Bigger heifers don’t always have the largest pelvic areas, and heifers of the same size can have drastically different pelvic areas. By pelvic measuring, producers can eliminate heifers that have proportionally small pelvic areas and eliminate any heifers that may have abnormally shaped pelvises.

Since pelvic area measurements are correlated to mature cows size and calf birth weight, it is a good idea to use this tool to set a minimum pelvic size as a culling criteria (ex. 140 cm2) rather than selecting heifers that have the largest pelvic area.

Conducting a BSE on heifers can help producers eliminate several potential problems and select heifers that have good reproductive potential. For those that wish to know more about reproductive tract scoring, pelvic measuring, or want the table containing the conversion factors, check out the Breeding Soundness Examination for Replacement Heifers publication under the Crops and Livestock tab on our website or give me a call.

For more information, contact the Marais des Cygnes Extension District Offices in Paola, 913-294-4306, and Mound City, 913-795-2829.

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