July 02, 2020

Interpretive Summary: Ractopamine-supplemented feedlot lambs

Interpretive Summary: Heat stress-induced deficits in growth, metabolic efficiency, and cardiovascular function coincided with chronic systemic inflammation and hypercatecholaminemia in ractopamine-supplemented feedlot lambs

By: Anne Wallace

Minimizing the impacts of heat stress is critical to the well-being and performance of livestock animals. Repeated and prolonged exposure to excessive environmental heat cause multiple negative effects, including poor growth and reduced feed intake. However, engineering interventions to reduce heat stress can be costly and may not be universally effective. Therefore, a better understanding of the physiological impacts of heat stress and practical ways to counter these effects in an economically feasible way are needed.

In this June 2020 Journal of Animal Science article, researchers evaluated how heat stress impacted the growth, metabolism and cardiovascular function of feedlot lambs. They also evaluated lambs for chronic systemic inflammation and excess production of catecholamines, which are typical but damaging responses to heat stress. The effects of ractopamine on the well-being lambs during heat stress was also evaluated. Ractopamine is a growth promoter given to feedlot animals to stimulate muscle growth and reduce fat.

One group of lambs was exposed to heat stress conditions while the other group of lambs was pair-fed but not exposed to heat stress conditions. All lambs were given ractopamine. In this study, heat stressed lambs had reduced blood pressure, heart rate and feed efficiency, reduced weight gain, and increased respiration, temperature and systemic inflammatory markers in the blood, compared to pair-fed lambs that were not heat stressed. The administration of ractopamine had no negative impacts on heat-stressed lambs.

Overall, the findings of this study suggest that heat stress negatively impacts the growth, metabolism, and well-being of lambs independent of reduced feed intake, as these unfavorable impacts were not observed in pair-fed lambs not exposed to heat stress. Future studies looking at how the negative effects of heat stress may be countered (e.g. phytochemical supplementation, probiotics, or prebiotics) may be warranted.