Does Supplementing Pregnant Cows with Protein During Winter Grazing Improve Calf Health?

Background

Extending the grazing season on cow-calf operations by adopting fall/winter grazing strategies is becoming more common due to reduced labor and cost, and the benefits to soil health and carbon cycling. However, mild nutrition deficiencies during pregnancy may have unintended long-term consequences on the calves. Protein, for example, is often insufficient to meet recommended levels when grazing corn and other dormant forages. Protein deficiencies can have negative impacts on the pregnant dam and the growing fetus. In addition to poor placental growth and reduced colostrum quality, protein deficiency can have negative impacts on the calf’s immune system development during gestation and after birth.

Crude protein (CP) supplementation has been found to increase body weight, BCS and improves post-partum reproductive efficiency. However, most of the previous work on supplementing CP to pregnant cows has focused on drylot systems in late pregnancy. Although the nutritional requirements in early and mid-gestation are relatively low, development of the immune system is happening throughout the pregnancy which could be impacted negatively by insufficient protein in extended grazing systems.

Objectives

The team is going to study the impact of winter feeding and protein supplementation on:

• Priming of antibody and cell-mediated immune responses during the pre-weaning period,
• Amount of memory T-cells/ T-cell plasticity during the pre-weaning period,
• Calf (calf vigor at birth, pre-weaned calf growth) and dam performances (body condition score, body fat, re-breeding length, body weight), and
• Activation of stress responses (expression of adrenergic receptors) in dams and calves, activation of immune memory cells, and stress responses of offspring.

Long-term, this research team wants to identify the mechanisms that regulate the immune programming of neonatal beef calves and develop approaches to mitigate the impacts of restricted maternal nutrition associated with extended fall/ winter grazing on low quality forage during pregnancy.

What they will do

32 cows (bred in late May to calve in late Feb) that are pregnant with their second calf will be grazed on corn from Sep/Oct to Dec/Jan, during the second trimester. Half will receive a protein supplement based on feed test results and NRC requirements. Because corn is low in protein, the cows that are not being supplemented will naturally be restricted. In the last trimester they will be fed hay in corrals with no nutritional restriction.

The team will collect monthly samples to assess forage digestibility, measure cow weight, BCS, backfat and blood cortisol pre-breeding (early-, mid- and late gestation, early- and mid-lactation), as well as calf birth weight, calving difficulty, and vigor score. Calves will be sampled (fecal, blood, nasal) at birth, 7 and 21days of age, at pasture turnout, weaning and 60 days post weaning to measure cortisol (a stress hormone) as well as systemic and mucosal immunity to respiratory and gut pathogens. The differential expression of genes related to the immune response will also be evaluated.

Implications

Winter feed and heifer development are two of the biggest input costs in the cow-calf sector, so finding ways to manage feed costs without compromising reproductive performance or calf health are key to economic viability in the cow-calf sector. Healthy calves also have lower treatment costs than immunocompromised ones. If protein supplementation while fall/winter grazing helps maintain healthy immune system development and function during gestation, then extended grazing could become an even more cost-effective, environmentally friendly wintering strategy without sacrificing calf health.