STILLWATER, Okla. - February 13, 2026 - Researchers from Oklahoma State University (OSU) and Kansas State University (KSU) clarified this week that restricting nutrients in bred heifers does not prevent calving difficulty and instead may compromise calf survival and long-term herd productivity. The findings matter as U.S. cattle producers prepare for spring calving amid tight margins, high input costs and record carcass weights influencing supply chain dynamics.

For decades, producers have been warned that supplementing protein during late gestation could increase calf birth weight and trigger dystocia. However, Paul Beck, OSU Extension beef cattle nutrition specialist, says the data tell a different story.

"Decades of research clearly demonstrate that maternal undernutrition during pregnancy negatively influences not only the cow's reproductive performance, but also immune transfer, calf survival, weaning weight and post-weaning performance," Beck explains.

Seminal OSU research from the 1970s compared heifers managed to maintain adequate body condition versus those in obese condition from 12 months through 5 years of age. At first calving, 58% of obese heifers required assistance, compared with just 8% of heifers in adequate body condition. These findings underpin today's recommendation that heifers calve at a Body Condition Score (BCS) of approximately 6, avoiding fleshy (BCS 7) or obese (BCS 8) targets.

Energy and protein supply during the final trimester can influence birth weight - but not always as producers assume. A 1975 study led by Corah demonstrated that heifers restricted to 65% of energy requirements during the last 100 days of gestation delivered calves averaging 4.4 pounds lighter. However, those lighter calves showed higher neonatal mortality and lower weaning rates. Reduced birth weight did not translate into less calving difficulty.

"Restricting nutrients prior to calving weakens both the cow and the calf, increasing calving difficulty and reducing calf survival," Beck summarizes.

A review of 24 late-gestation supplementation studies found the average increase in calf birth weight was only 3 pounds, with responses ranging from a 3-pound decrease to a 10-pound increase. The largest increases occurred when high levels - about 5 pounds per day of energy-dense supplement - were fed. Importantly, among 15 studies reporting subsequent pregnancy rates, supplemented cows averaged 92% pregnancy rates, compared to 86% in unsupplemented cows, with the greatest benefit seen in first-calf heifers.

According to Jaymelynn Farney, KSU beef systems specialist, late-gestation restriction may also reduce colostrum quality and immunoglobulin absorption. Calves from underfed dams can be weaker, slower to nurse and more prone to scours, directly affecting weaning weights and overall herd profitability.

Excessive energy intake - not protein alone - is the main nutritional factor tied to increased dystocia risk. When surplus energy is directed toward fetal growth and fat deposition in the pelvic region, calving assistance rates rise. Balanced nutrition, rather than restriction, remains the optimal strategy.

Farney notes dystocia is multifactorial. Causes include calf size, small pelvic area, abnormal presentation, uterine inertia, fatigue or twins. Genetics also play a role. High calving-ease sires often shorten gestation length, reducing birth weight by 10 to 14 pounds if calves arrive a week early.

Environmental stress is another overlooked factor. A Nebraska study found that for every 1°F drop below average winter temperatures, calf birth weight increased by 1 pound, likely due to increased supplementation to offset cold stress. Attempting to avoid calving difficulty by failing to meet added maintenance requirements can create long-term productivity losses.

"Don't starve the calving difficulty out of your heifers," Farney cautions. "These heifers need appropriate energy to complete parturition, and calves need enough vigor to stand and nurse quickly. Protein is essential for colostrum quality, which has lifetime impacts."

As U.S. cattle operations navigate volatile commodity prices and rising feed costs, the research underscores a central message: meeting - but not greatly exceeding - energy and protein requirements while targeting a BCS 6 at calving improves calf survival, immune function and long-term reproductive efficiency without increasing dystocia risk.

Avoiding maternal undernutrition remains one of the most consistent strategies for improving whole-herd productivity and profitability in today's beef industry.