Veterinary Handbook Disease Finder

Veterinary Handbook Contents

14.1 Wet Bulb Temperature Rise

A series of MLA-funded projects in the early 2000s led to a better understanding of ventilation on board export vessels and recommendations about vessel design (including modifications that could be made to existing vessels) to improve ventilation and reduce heat stress risk. In addition, a software program was developed for heat risk assessment, which is owned by LiveCorp and MLA and distributed to licensed livestock operators for use in assessing and managing heat stress risk on long haul voyages. 

The Heat Stress Risk Assessment (HSRA) software incorporates a range of inputs about expected climatic conditions on a proposed voyage that allow prediction of ambient wet bulb temperatures on that route at that time of year, and about animals (such as species, breed, level of acclimatisation and weight). In addition, vessel specific parameters describe things such as pen and deck area, and performance of mechanical ventilation on each deck (measured as pen air turnover or PAT). These parameters form inputs into a computer model that predicts wet bulb temperature rise (the rise in temperature within a deck that may be attributed to the combination of ambient conditions, PAT values for specific vessels, and heat produced by the animals in that deck). 

The software also incorporates current knowledge concerning the ambient wet bulb temperature and risk of animal mortality for different types of animals. The software then uses the predicted wet bulb temperature rise to estimate the probability of 5% mortality from heat stress. The program then allows adjustment to the stocking density as a method of lowering the wet bulb temperature rise for the proposed voyage such that there is a less than 2% probability of a 5% mortality event occurring. 

The use of the HRSA software is now incorporated into the formal risk management process for long haul voyages. It should be noted that at the time of writing, following the completion of the McCarthy Review (2018), the HSRA software will be reviewed together with the assessment/indicators of heat stress.