Producers are often told supplementing bred heifers with protein prior to calving increases calf birth weight and leads to greater calving difficulty.
According to Paul Beck, Oklahoma State University (OSU) Extension beef cattle nutrition specialist, nutrition of bred heifers during gestation does have lasting consequences for both the calf and the future productivity of the cow.
“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,” he says.
Research conducted in the 1970s at OSU compared productivity of heifers managed to achieve either adequate or obese body condition from 12 months through 5 years of age. At first calving, 58% of the obese heifers required calving assistance, compared with only 8% of heifers at adequate body condition. These data are the basis for current recommendations that heifers calve at a body condition score (BCS) of approximately 6, but not reach a fleshy (BCS 7) or obese (BCS 8) condition.
Energy and protein supply during late gestation can influence calf birth weight, Beck summarizes. Research by Corah and colleagues published in 1975 demonstrated heifers restricted to 65% of energy requirements during the final 100 days of gestation produced calves approximately 4.4 lb. lighter at birth. However, these calves experienced greater neonatal mortality and reduced weaning rates compared with calves from adequately fed dams. Importantly, lighter birth weight was not associated with reduced calving difficulty, illustrating how undernutrition compromises calf viability rather than preventing dystocia.
“Restricting nutrients prior to calving weakens both the cow and the calf, increasing calving difficulty and reducing calf survival,” Beck summarizes.
Kansas State University’s Jaymelynn Farney says restricting heifer diet in the last trimester can result in potentially lower quality and quantity of colostrum, reduced absorption of immunoglobulins from colostrum potentially driven by weaker calves that were slower to nurse, an increase in calf scours and a reduction in overall weaning weights.
Birth weight responses to precalving supplementation are highly variable. Beck evaluated changes in calf birth weight reported from 24 studies evaluating late-gestation supplementation.
“The average increase in calf birth weight was only 3 lb., with responses ranging from a 3 lb. decrease to a 10 lb. increase,” he reports. “The largest increases occurred when high levels (approximately 5 lb. per day) of energy-dense supplements were fed.”
Fifteen of these studies also reported subsequent pregnancy rates. Although variable, the average pregnancy rate of unsupplemented cows was 86%, compared with 92% for cows supplemented during late gestation, with the greatest response observed in first-calf heifers.
Excessive energy intake during late gestation partitions more nutrients toward fetal growth, resulting in larger calves. When coupled with excess fat deposition in the pelvic region, this increases the risk of dystocia. Thus, excessive energy, rather than protein supplementation alone, is the primary contributor to increased calving difficulty in many heifer programs.
Ensuring bred heifers meet — rather than greatly exceed — energy and protein requirements, promoting moderate BCS gain during mid and late gestation and strategically supplementing key nutrients improves calf survival, preweaning growth, immune function and long-term reproductive performance without increasing calving difficulty.
“Avoiding maternal undernutrition remains one of the most consistent strategies for improving whole-herd productivity and profitability,” Beck summarizes.
What Causes Calving Difficulty?
Farney says there are multiple reasons calving difficulty can occur, which may include the calf being too big, pelvis too small, abnormal presentation, lack of uterine contractions, fatigue or twins.
“Abnormal presentations cannot be eliminated by genetic selection or nutritional management, so be prepared for these scenarios a minimum of three weeks before your first calf is expected,” says Farney, a beef systems specialist.
Calf birth weight is often blamed as the sole culprit of calving issues.
“Calf birth weight can be affected by several factors — genetics, gestation length and, to an extent, dam nutrition,” Farney summarizes. “High calving ease sires typically have a shortened gestation length, hence the reason that most of those calves are a bit lighter in weight.”
She says on average, calves will gain between 1.5 lb. to 2 lb. of body weight in late gestation. For example, if the average gestation length is 283 days and a calf is born a week early, it will often weigh 10 lb. to 14 lb. less.
She adds dams that experience cold stress in the last trimester may have calves that are heavier in weight.
“Typically birth weights are greater for calves born in the spring or winter as compared to fall-born counterparts,” she says. “A Nebraska study that evaluated six years of data found for each 1° F lower than the average winter temperature (December through February) calf birth weight increased 1 lb.”
The increase in birth weight is most likely due to the needed increase in nutrient flux through supplementation to offset cold stress events.
“Now you might think, it is a cold winter and I do not want to deal with calving problems, so I will just make that cow survive on the same diet she has been on and not account for added maintenance requirements due to cold stress,” Farney says. “That thought will lead to a plethora of other issues that can extend through that calf’s entire productive life.”
She stresses it is important to appropriately balance a diet for first-calf heifers.
“Don’t starve the calving difficulty out of your heifers,” Farney summarizes. “These heifers need appropriate energy to help with the birthing process or they will quit on you as they just run out of steam going through parturition. Additionally, the calves need enough energy to quickly get up and nurse, and if dam energy is restricted, calves will be lethargic. Proteins are essential for colostrum quality, which has major lifetime effects on that calf.”
Your Next Read: Feeding at Dusk: How Does This Affect Calving Times?
