Measuring Microclimate Variations In Two Australian Feedlots

Summary

Heat stress has caused catastrophic stock losses infrequently in Australia and does cause production losses over summers. While a considerable body of research has been undertaken on defining heat stress with respect to cattle comfort, health and production, few data are available on the micrometeorological characteristics of feedlots, shaded pens in feedlots and differences between feedlots and their surrounds. A study was undertaken to define these microclimates and therefore to identify the probable causes of heat stress.

The objectives of the study were to:

1. Establish a series of weather stations at two feedlot sites (southern NSW and Queensland) by 30 December, 2000.

2. Measure and quantify the magnitude of microclimate variations that occur within the feedlot pen area as a result of the effects of: Topography; Aspect; Relative position within the feedlot pen area; Provision of shade; . Adjacent structures.

3. Verify, collate, and interpret the collected data to establish the relationship between ambient weather conditions and conditions experienced by animals within the feedlot pen area.

4. Document and present the findings to industry and producers. This study aimed to provide feedlot managers with a better understanding of the connection between cattle behaviour, the physical environment, and micrometeorology. It is hoped that the information presented will enable the design, layout, and management of feedlots to be better adapted to reduce the potential for cattle losses caused by extreme weather conditions.

The study found that feedlot climates are different to their surrounds. Generally they are hotter and more humid and have lower wind speeds under shade. The study found that shade benefit cattle by reducing radiation heat loads but have the deleterious effects of increasing manure moisture contents, relative humidity and ammonia levels. Ammonia is identified as a possible stressor but its importance must be further defined.

The study has shown that gross heat load is influenced most by the generation of heat within the body through metabolic processes and the loss of heat by convective means. In the latter case, continuously high temperatures (daytime and night time) limit the ability of the animal to shed heat and therefore act as the key stressor of stock. Potential stress events can be forecast and mitigation measures can be utilised.