Evaluation of a heat load model for feedlot cattle

Summary

​The Heat Load Index (HLI) model (Gaughan et al. 2008) was developed by monitoring panting scores of commercial feedlot cattle across a range of sites in Australia and the United States.

When the HLI and Accumulated Heat Load Unit (AHLU) models were first published in 2008 it was always the intention that at some point the models would need to be reviewed. Over the last few years there has been some concern that the models do not always adequately reflect what lot feeders are seeing in the field.

In many cases, anecdotal observations suggest the models work very well. However, in some cases, the models suggest that cattle should be adversely affected by high levels of accumulated heat load when in reality the cattle cope with no signs of stress. At other times the model underestimates the effects on cattle. While this is not the case for all locations at any given time, false alerts or a failure to alert results in a loss of confidence in the usefulness of the models by the end-users.

Some of the failures may be due to incorrect siting of the weather station (i.e. not truly representative of conditions in feedlot pens) and incorrect threshold settings (e.g. threshold set as if all pens are unshaded). However, at some locations there appears to be a difference between animal responses and the predicted responses based on the models. Further investigation of model adequacy was implemented in this MLA research project.