Reducing heat load – nightime feed intake, and strategic use of bedding.

Summary

**Please note that the feedlots wish to remain anonymous and all identifiers have been removed from the data. The project was approved by the University of Queensland Animal Ethics Committee.

The study was undertaken to determine the following:Determine the impact of weather conditions on the feeding behaviour of feedlot cattle during summer.Determine the relationship between weather conditions, body temperature and feed intake during summer.Develop feeding strategies that will enhance heat dissipation at night.Determine the effect of straw bedding as a tool to alleviate heat load in feedlot pens.
A pilot study was undertaken to determine the best options for video camera placement (for the main study), surgery techniques for i-button placement (for recording body temperature), and hay usage for pen surfaces (strategic use of bedding).  The findings from the pilot study are presented in the Milestone 1 report for this study,
Cattle in three commercial feedlot were used in the studies which ran over the summers 2015/16 and 2016/17. A number of animals were implanted with temperature loggers (which were removed at slaughter and the data downloaded). The loggers were set to record at either 1 hour or 10 min depending on the feedlot and the duration of observation. Body temperature profiles were determined and the rate of heat gain/loss was determined.
Two important outcomes from this study are: (i) increase heat load leads to an apparent disruption to the heat/gain regulation in both Bos taurus and Bos indicus steers, (ii) cattle will self-regulate and the consumption of feed and associated activity appears to lead to a small but significant increase in body temperature eat night. Thus it is somewhat difficult to develop succinct feeding strategies to ameliorate heat load, and (iii) cattle tended to stop eating when body temperature was increasing, and commenced eating when body temperature was decreasing and heat load was decreasing.
The feed intake data is somewhat limited but it appears that once HLI drops below 90 to 95 (there are other factors which make a precise value difficult to define at this time), and it appears to change somewhat from day to day. It also appears that body temperature is the main driver, not so much the magnitude but whether or not body temperature is falling.
Due to logistical and weather factors the bedding component of the study was not completed.
The recommendations arising from this study are:Determine how the observed changes in body heat/gain will influence the calculation of the accumulated heat load. Adapt the model as required.Further investigate the body temperature profiles of Bos indicus cattle.Evaluate the body temperature data form FLOT.0157 to further investigate changes in body heat/gain. Data is available from climate rooms as well as outdoor feedlot pens.Further investigate how body heat/gain is affected by heat waves.In regards to conclusion 2 – need to determine if the slow release of heat at night can be speeded up to ensure optimal body temperature as cattle enter a new day.
 In regards to conclusion 4 - biologically we are not sure what this means but it needs further investigation