Investigation of the Ventilation Efficacy on Livestock Vessels

Summary

The live cattle and sheep trade from Australia to the Middle East and North Africa has expanded rapidly since 1995. Although mortality rates have been low overall there has been no scientific investigation into the causes of disease or mortality or of the predisposing factors. There were 60 cattle voyages from Australia to the Middle East in 1997. The average death rates for these shipments was 0.6%.

Similarly the mortality rate from 119 cattle voyages during 1998 was 0.6%. Recent instances of excessively high mortality levels on voyages to the region have focussed industry's attention on this issue and led to several initiatives aimed at improving the welfare of the animals and minimising death rates. However, in the absence of sufficient research into the causes of livestock disease and mortality at sea, there has been no scientific basis on which to found these initiatives.

One such initiative is an investigation of ventilation efficacy on livestock vessels. It has been suggested that inadequate ventilation may contribute to mortality or unsatisfactory welfare of livestock during the voyage. In addition, there is a need to review ventilation performance on livestock vessels and to develop minimum standards for such vessels. This report describes the first of six voyages from Australia to the Middle East to be monitored as part of the study "Investigation of Ventilation Efficacy on Livestock Vessels" commissioned by Meat and Livestock Australia. The study commenced with a literature review, the purpose of which was to:

Summarise the available relevant literature to give a solid platform of knowledge.
Identify a model which describes the physiological risk of animals to given environmental conditions.
Guide the shipboard experimental programme as to the real issues and appropriate measurements to be taken. Some familiarity with the earlier literature review is assumed and so the background to the environmental indices ETI (effective temperature index) and THI (temperature humidity index) and the scientific basis for the work is not restated here. The aim of the shipboard work is to investigate the linkages between ventilation and livestock health and comfort. A range of measuring techniques has been applied to assist in this. From the review work, the target outcomes for the first voyage were set as:
Measure key aspects of ventilation.
Record key indicators of livestock health and comfort.
Measure key parameters of the ambient and below-decks environmental conditions.
Account for predisposing factors such as prior handling, breed type and acclimatization.
Develop a template to assist data entry and analysis on subsequent voyages.
Provide a set of data to either confirm the applicability of the physiological model or indicate amendments required. Conclusions This first voyage was considered a success in generating significant and useful data. Of course it was never expected that the first voyage would yield all the answers and three particular changes have been made for the second voyage;
​(i) more frequent measurement of overall conditions will be attempted,
(ii) pens selected for monitoring will include some close to and some remote from the main exhaust points, and
(iii) an attempt will be made to assess heat from ship sides and manure beds.
​At the completion of voyage 1, a number of key points can be made:
Accounting for airspeed in ETI improves the correlation with observed respiration rate.
THI is not so well correlated with observed stress.
Ammonia levels can be high in terms of published criteria however the health effects on the cattle are yet to be determined.
Overall ventilation rate (air changes/hour) is important in the control of ammonia.
In controlling heat (or ETI) and CO2. the fresh air rate per 500kg body weight is more important than the rate in air changes per hour.
Local jetting of air (higher airspeed) reduces ETI and is likely to assist cattle.