B.FLT.0157-Heat load nutrition program

Summary

Heat stress in cattle is a recognised welfare and production issue in the feedlot sector. The main objective of this research program was to provide recommendations for nutritional management of feedlot cattle during periods of high heat load during summer. We undertook two approaches in measuring and understanding the metabolic and inflammatory impacts of high heat load by running feedlot trials over summer and winter seasons, and under the controlled conditions of the climate chamber.

Our working hypothesis at the start of this program, was that high heat load causes loss of gut integrity, leading to systemic inflammation that generates more heat load and thus exacerbates the problem, resulting in further organ damage and eventual loss of homeostasis and thermoregulation. To find evidence for these events, the program conducted seven feedlot trails (of 70 – 110 days) and four climate chamber experiments of increasing heat load. The acute high heat load regimes were designed to mimic a strong heatwave event. In all trials and experiments, the cattle were on a finisher ration.

Objectives

- Provide recommendations for nutritional management of feedlot cattle during summer, and/or during periods of high heat lead, to improve productivity and welfare of feedlot cattle through: establishing the need for nutritional strategies to manage heat load through the high risk periods of summer, or all of summer feedlot studies and understand the impact of heat load conditions on immune status, and the altered metabolic and inflammatory responses induced by these conditions.
- Develop new nutritional interventions and management strategies before, during and after heat load events.
- Increased ongoing nutritional research capability for industry through training and monitoring of a postdoctoral fellow at the University of Queensland.

Key findings

- The feedlot steer is very adept at invoking mechanisms to adapt to increased heat load. However, sudden intense heat wave events have serious physiological and metabolic consequences for the heavy feedlot steer (i.e. Black Angus). The immediate response is to reduce internal heat production by markedly reducing feed intake and metabolic rate, and increase cooling by increased respiration and shunting blood to the skin. Following the heat wave, the liver and the rumen, and possibly the kidneys, take time to recover. However, there is no evidence for gut damage and uncontrolled inflammatory responses in the healthy animal coping with heat stress.
- We have developed a robust and reproducible methodology to test a wide variety of interventions to ameliorate heat stress in the feedlot steer. For example, we investigated the timing of introduction of the ‘heat load’ ration and showed that changing the ration at the same time as the onset of the heat wave resulted in poor outcomes the animals and productivity; and worse than no change to ration at all. Introduction of the ‘heat load’ ration two days prior to a heat wave could be more effective.

Benefits to industry

This project has established a replicable model of high heat load to test nutritional interventions. The research project highlights the importance of placing cattle on a diet with increased roughage content prior to the heat load event.

MLA action

MLA has presented the results of this research to the ALFA/MLA Consulting Veterinarian and Nutritionist meeting. Producer articles were also prepared for the ALFA journal on timing of heat load ration implementation. Peer reviewed articles have been published from research findings.

Future research

MLA has presented the results of this research to the ALFA/MLA Consulting Veterinarian and Nutritionist meeting. Producer articles were also prepared for the ALFA journal on timing of heat load ration implementation. Peer reviewed articles have been published from research findings.