Make Calving Difficulty Minimal
with the Right Heifers and Bulls
By Jason Cleere, Ph.D.

It only takes a slight drop in the percentage calf crop weaned each year to really impact cow-calf operation income.

      Standardized Performance Analysis (SPA) data for 1991 to 2005 indicate the most profitable cow-calf operations weaned five percent more calves than the least profitable herds (85 percent calf crop versus 79.8 percent calf crop).

      Most reproductive losses occur because cows fail to become pregnant or from calf losses at or near birth.

      Research trials and practical experience tell us first-calf heifers calving at two years of age have a much higher risk for dystocia than three-, four- or five-year-old cows. The most common cause of dystocia or calving difficulty is heavy birth weight and/or small pelvic area of the dam.

      Calves surviving a difficult birth can be weak and have a fourfold increase in death loss.

      Heifers that experience dystocia will have a longer postpartum interval and lower rebreeding rates than females with no calving problems. Calving difficulties also mean more labor costs and veterinary expenses.

      Genetic selection and proper heifer development programs are important to reducing the risk of dystocia in replacement heifers. Select heifers for adequate skeletal size and pelvic area and provide the proper nutrition during pre-breeding until calving to reduce calving problems.

      Just as important, if not more, select a bull to breed these heifers that will produce calves with low birth weights.

Heifer selection and development

      Replacement heifers are 10- to 15-year investments and the selection process should not be taken lightly. Select females that will produce a calf born unassisted beginning at two years of age and every 12 months thereafter.

      Research has shown a major cause of dystocia is the incompatibility of the calf’s size with the area of the heifer’s birth canal or pelvic area. Select heifers with a larger pelvic area to help reduce the risk of dystocia.

      Oklahoma researchers found heifers with a small pelvic area had an 85 percent incidence of calving difficulty. Heifers with acceptable size had only a 31 percent rate.

      Heifers with larger skeletal size will typically have a larger pelvic area. Producers can use skeletal size as a tool to select heifers with adequate pelvic area. However, too much selection pressure on frame size can lead to increased mature cow size over time and higher maintenance requirements and costs.

      Select heifers born in the first 30 to 60 days of the calving season. These heifers tend to be heavier at weaning and better able to achieve the proper weight needed for onset of puberty. They also tend to be calves from the most fertile cows that conceived early in the breeding season.

      If selection for adequate skeletal size and use of low birth weight bulls does not control dystocia in your herd, use a more objective method of estimating pelvic area.

      Cow-calf producers can physically measure the dimensions of the pelvis and cull those heifers with less than 140 cm2 of pelvic area. Measurements are obtained rectally pre-breeding using a Rice Pelvimeter or Krautmann-Litton Bovine Pelvic Meter.

      Proper heifer development is just as important as selecting heifers with genetically larger skeletal size. Optimal nutrition from weaning until calving is required to ensure proper skeletal development. Develop heifers to a pre-breeding target weight of 65 percent of their projected mature weight and to a pre-calving target weight of 85 percent of their projected mature weight.

Bull selection

      The most effective way to minimize calving difficulties is by using bulls known to produce lighter birth weight calves. Breed of bull is an important factor to consider. Average birth weights will vary between breeds, and some are known to have lighter or heavier weights than others. However, don’t completely sacrifice the performance or marketability of a heifer’s first calf to ensure she and her calf survive calving. Many breeds have low birth weight genetics and acceptable growth.

      Birth weights will vary considerably within breeds and there are several selection tools to assist with the decision.

      Consider the actual birth weight of the bull, but realize this is not the most accurate tool.

      Birth weight expected progeny difference (EPD) and calving-ease EPD are the most accurate information to select low birth weight or calving ease bulls.

      Birth weight EPD is expressed as the difference in pounds of birth weight from a bull’s offspring. A general rule is to select bulls with EPDs below the breed average for use on heifers.

      Calving-ease EPD is expressed as the difference in the percentage of unassisted births when bred to heifers. Consider using bulls with EPDs above the breed average.

      It is important to remember that average birth weights vary considerably between breeds. Just because a bull has a birth weight EPD below average within his breed does not necessarily guarantee he is the best bull for first calf heifers.

This series in the Rancher’s Management Guide is provided by the Texas Beef Partnership in Extension program and program sponsors. Click here to see past articles.