Heat stress nutrition: A comprehensive review and R&D program

Summary

​The cattle feedlot industry is cognisant of society’s oversight of the welfare of animals in their care, the economic demand for increased productivity, and the increased climatic variability of Australian beef production regions. Over the last two decades, the industry and MLA, through learning from experience and with investment in R&D have overcome the extreme effects of heat wave events. Nonetheless, there is recognition that high heat load experienced by cattle in feedlots continues to be detrimental to their welfare and growth.

Despite considerable R&D investment by MLA and researchers internationally over several decades, limited inroads have been made into the development of successful nutritional strategies to offset or ameliorate the effects of heat stress. Many of the ‘off-the-shelf’ feed additives have been trialled and found to have no or equivocal improvement to productivity or cattle comfort. These outcomes highlight the necessity of looking deeper into the altered physiology and metabolism of feedlot cattle over the summer period and during heat waves.

From a review of the literature, and discussion with overseas researchers, it became apparent that rumen and gut health is most likely at the centre of high heat load morbidity and poor recovery after heat stress. The sometimes promising and then disappointing results of the nutritional intervention studies may have arisen from poor understanding and control of the stress-related inflammatory status of the animal. The complexity of needed studies and often time discouraging outcomes deterred investigation into opportunities for the strategic use of nutritional interventions prior to, and through to recovery from acute or chronic (modest but long duration thermal discomfort) heat events. As a consequence, the biology of the animal recovering from hyperthermia is not well understood.

With input from industry representatives, a 5-year R&D program was designed to deliver new nutritional strategies for a forecast heat event (including pre-emptive and post-event interventions) and investigate the need for management during summer high risk period and/or all of summer. To ensure that any recommended intervention is applied to gain the optimal result, the program intends to understand the altered metabolic and inflammatory responses induced by high heat load.

On this basis, a 2-stage approach for future R&D has been proposed: firstly, use of very controlled conditions followed by pen trials to validate altered inflammatory and metabolic status and gut barrier disruption; secondly, applying the knowledge from stage 1, nominate and test the potential use of commercially-feasible feed additives that could ameliorate the changed state in the feedlot animal.