If the spring-born calves aren’t weaned yet, then the time isn’t far away now that fall is here. This month we’ll look at recent research from Philipe Moriel and others at North Carolina State University (NCSU) on the role of maternal nutrition in calf performance and health.
Veterinarians and ranchers know healthy weaned calves begin with a well-vaccinated cowherd long before calving, because high-quality colostrum minimizes disease exposure for nursing calves. All true, yes, but even the best established herd immunity can fall short if nutrition falls short in the days before calving.
Work from the 1970s told us calves born to nutrient-restricted cows were more likely to be treated for bovine respiratory disease (BRD) with greater death loss than calves from cows with adequate nutrition. More recent Nebraska field trials suggest protein supplementation to pregnant cows during the last trimester of gestation improves carcass quality grade and weights in steer progeny while decreasing puberty age and improving pregnancy rates in heifer calves compared to those from unsupplemented dams. These studies demonstrated the potential impact of extended nutrient restriction in late gestation.
Moriel’s work suggested an energy restriction of 30 percentage points for as little as 40 days would be sufficient to reduce calf growth and health after weaning. Now many weaning pens are full and calves are on their way to realize whatever potential they hold. But it won’t be long till the first 2017 calves arrive, and it’s time to begin planning for a successful weaning next fall.
In the NCSU trial, mature Angus cows pregnant by embryo transfer (to eliminate calf genetic differences) were split into two groups at 8 months of gestation and fed either 100% of energy requirements or restricted to 70% of energy requirements. Both groups received adequate protein, consistent with Eastern forage-based cow diets where energy is restricted but not protein. As expected, restricted cows lost more weight (35 pounds) in those last 40 days before calving, but body condition scores were reduced only slightly (0.25 units). There were no differences in gestation length, and pregnancy rates the next year were numerically greater for the restricted cows. That all goes to show cows may experience a significant nutrient restriction, unnoticed by changes in body condition or function.
Contrary to the researcher’s hypothesis and previous experiments, calf birth weight, pre- and post-weaning growth rates were not different due to dam nutrient restriction. The short-term duration (40 days) was suggested as the reason.
Fetal growth isn’t the only important biological activity in the last trimester; let’s not forget colostrum development during the last month. Previous work suggests undernourished cows are unable to provide quality colostrum, so calves in this experiment were tested to determine if colostrum quality was sufficient to provide passive immunity. Regardless of the cow’s nutritional status in this experiment, all calves demonstrated adequate immunoglobulin levels for passive immunity.
Calves were vaccinated 7 days after weaning and boostered 14 days later for respiratory and clostridial diseases, per a local pre-conditioning protocol. Still, there were no differences in titers for one species of bovine viral diarrhea (BVDV-2), or infectious bovine rhinotracheitis (IBRV) or parainfluenza3 (PI3) due to cow nutrition, but the study was about to hit pay dirt.
The calves from restricted cows expressed lower BVDV-1a titers, suggesting that 40-day energy restriction at the end of gestation suppressed vaccination-induced immunity. Lower concentrations of cortisol and haptoglobin (stress and infection indicators) were also observed in those calves, suggesting the endocrine stress response was also modified during gestation.
This report is a great example of the unseen but real effects from a short-term nutritional challenge at the ranch. In this case, the calves became predisposed to post-weaning illness further down the supply chain. We know health is one of the most important aspects of quality beef production, so begin making plans to give calves the best chance to stay healthy on your place, and beyond, by evaluating your cows’ nutrition now and before those last 40 days start ticking off.