Evaluation of feedlot heat load model adjustments

Summary

Feedlot producers currently use an online forecasting service – the Cattle Heat Load Toolbox – to proactively manage hot weather events each summer.

To follow on from a previous MLA project, which found that accumulated heat load units (AHLU) significantly altered the heat load response of feedlot cattle, this study conducted further evaluation of the heat load at two south-east Queensland feedlots.

In an unshaded feedlot, yard, day and pen type accounted for 28% of the variation in explaining higher panting scores. At a shaded feedlot, Wagyu cattle demonstrated higher heat tolerance to heat than Bos taurus cattle.

Objectives

The primary aim of this project was to determine the adequacy of model adjustments proposed in MLA Project B.FLT.0387 to explain the proportion of cattle of different breed types with a panting score equal to, or greater than, 2. A higher panting score indicates higher levels of heat stress in cattle.

Key findings

• Adjusting AHLU for different breed types significantly increased the accuracy of predicting the probability of cattle having a panting score equal to, or greater than, 2.
• Random effects (yard, day and pen type) accounted for 28% of the causes of an increased panting score, which makes them important variables to consider when using the Heat Load Model.
• Wagyu cattle demonstrated higher heat tolerance than Bos taurus cattle when held at a shaded feedlot.
• Cattle that have 50% Bos indicus heritage have a higher heat tolerance than cattle that are only 25% Bos indicus.

Benefits to industry

The heat load model available in the Cattle Heat Load Toolbox helps feedlot producers predict the heat load of cattle, however, it requires some improvements to suit all breed types, regions, pen locations and times of day.

This information will help guide positive changes in husbandry and best practice management to improve the health and welfare of feedlot cattle during hot summer periods.

MLA action

MLA continues to fund the heat load forecasting service for the Australian feedlot industry. Future research may investigate alternative modelling approaches to improve the accuracy of the heat load model.

Future research

Further research is required to build a robust heat load model for the Australian feedlot industry.

To build a robust heat load model requires a huge number of observations across multiple regions, market categories, breed types. Once affordable and accurate technology becomes available, future heat load models may rely on measurement of individual panting score and respiration rate through wearable devices.