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in this project for southern cattle in Summer may in fact be the result of increased animal mixing and density and not directly due to seasonal factors.
It is likely that a combination of general and targeted risk mitigation measures may be appropriate for reducing morbidity and mortality risk in export cattle. General measures may
be based on management practices to reduce stress and co-mingling. Specific measures may involve the use of more targeted interventions that may be associated with additional
costs, such as vaccine or medication. If there is available information to identify higher risk groups of animals, then interventions may be applied to those groups and not to all animals,
as a way of ensuring cost-effective risk management.
12 General discussion
This project originated in part from concerns over respiratory disease as a cause of mortality in cattle exported from Australia to the Middle East. An initial scoping study was completed
to assess design options for a project to investigate causes of death in exported cattle and more specifically respiratory disease, as a specific cause of interest. This project was then
designed and implemented as a result of that process.
This project has been a large, complex and innovative undertaking. A key feature of this project was the collaborative and innovative approach to involving
exporters and their staff -- particularly AAVs -- in the process of collecting and contributing research data and information.
This approach ensured that we could enrol a larger number of voyages and collect information from a larger number of mortalities than would have been possible if all data
collection had been undertaken by members of the research team.
This approach also meant that we had to limit our data collection procedures to priority activities, because we were asking AAVs to undertake activities and complete forms for the
research project while they had to complete all their routine day-to-day activities as well.
A second key feature of this project is that it has contributed to development of a substantial body of resource information and training material about optimal management of animal
health and welfare during export and investigation of morbidity and mortality.
Finally this project has delivered against all of the objectives in the terms of reference and has advanced our understanding of causes of mortality in export cattle.
12.1 Causes of death
This project has described the major causes of death in cattle exported from Australia to long haul destinations including the Middle East Israel, Saudi Arabia, Bahrain, North Africa
Egypt, Libya, Turkey and the Russian Federation Russia. The findings are likely to be applicable for all long haul cattle voyages.
The most important cause of mortality in the voyages studied was bovine respiratory disease BRD, accounting for 50 of deaths that were investigated. This was followed by
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musculoskeletal and injury-related conditions that were responsible for another 15 of deaths.
It is also noteworthy that BRD was identified as a concurrent disease in one third of animals where the primary cause of death was assigned to any condition other than respiratory
disease. Our findings do not indicate whether BRD in these cases may have preceded other diseases, i.e. whether BRD may have been the primary disease and increased the
predisposition of an animal to another disease that ultimately killed the animal, or whether BRD in these animals may have been a secondary complication of the other conditions.
The two most important causes of death accounted for 65 of all mortalities. Other causes of death were responsible for 1 to 6 of mortalities, representing relatively
minor contributions to overall mortality counts. Ketosis inappetence accounted for 6 of mortalities, but was observed mainly in pregnant
breeder animals and may not be an important cause of death in feeder slaughter animals. Septicaemia was the primary cause of death in 5 of mortalities.
Enteric disease diseases of the gastrointestinal tract was the primary cause in 5 of mortalities.
Heat stroke was identified as the primary cause of mortality in only 1 of deaths. The cause of death could not be determined in 16 of cases.
12.2 Diagnosis of causes of death
Our findings suggest that BRD can only be diagnosed effectively during a voyage as a cause of death using a combination of ante-mortem observations and gross necropsy. Clinical
observations of sick animals ante-mortem records are not sufficient to identify cases of BRD with confidence. This is an important finding and is likely to reflect difficulties in
detecting clinical signs and inability to physically examine individual animals during the voyage, the fact that some animals may have severe disease and not show much overt
clinical signs and that the clinical signs that are displayed may not be very specific for BRD and may be due to any of a number of different underlying diseases.
Musculoskeletal conditions and injuries can be effectively diagnosed as a cause of death using ante-mortem observations. This is likely to be because affected animals display
obvious clinical signs such as gait abnormalities, reluctance to move or inability to stand, that can be detected readily by general visual inspection of pens. Gross necropsy remains useful
even for animals with visibly noticeable musculoskeletal conditions because gross necropsy will determine whether other conditions such as respiratory disease may have contributed to
death in an animal with a musculoskeletal injury.
Other conditions can only be reliably diagnosed by gross necropsy. There are constraints during the voyage associated with the general scale of decks and
pens and animal numbers and difficulties in moving, restraining and examining or treating individual animals. These constraints mean that it is difficult to reliably record specific clinical
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observations on individual animals or to detect development and progression of clinical signs within individual animals. These same constraints are present in land-based feedlots.
As noted in the Veterinary handbook for the live export industry
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, it is possible to generally inspect large numbers of animals using inspection methods detailed in the handbook. These
are based on visual inspection of animals in pens and will reliably detect non-specific signs that are indicative of serious disease, particularly when there are multiple animals that are
affected. For musculoskeletal and injury conditions these visual inspection methods may be sufficient to detect individual animals and identify the general disease category
musculoskeletal disease or injury with confidence. Visual inspection of animals in pens will not reliably allow diagnosis of specific diseases such as BRD, because such methods detect
non-specific signs that may be common to many different diseases.
It is not practically feasible nor necessary to have every single animal that dies during a voyage be subjected to a detailed and comprehensive necropsy with a range of biological
samples and digital images collected for subsequent examination and testing in a pathology laboratory to determine the cause of death.
However, It is important that AAVs conduct gross necropsy examinations of animals that die during a voyage where possible. For voyages that do not have an AAV on board, the senior
stockperson should receive sufficient training to be able to conduct a necropsy with confidence and describe gross changes in key organs, particularly lungs and selected
abdominal organs.
We have developed simplified procedures during this project for conducting gross necropsies on a subset of dead animals to ensure maximal information is derived from
necropsies while also minimising the time required to perform necropsies. These procedures have been described in the Veterinary Export Handbook W.LIV.0252 and were applied
during the research activities for this project, however they are not currently described in the Veterinary handbook for the live export industry.
It is recognised that these procedures may not be sufficient to provide maximal likelihood of identifying all causes of death. In addition, not every dead animal is likely to be necropsied.
The use of targeted or simplified necropsy procedures will allow reliable identification of the major known causes of death in export cattle. In those voyages where larger numbers of
mortalities occur, this approach will ensure confidence in distinguishing the relative contributions of major causes of death, such as BRD vs heat stroke vs enteric conditions or
musculoskeletal conditions.
The key principles are as follows: Gross necropsy should be focused on identifying the major recognised causes of death
occurring during export voyages: BRD, musculoskeletal injury, inappetence, enteric disease, heat stroke.
Where multiple deaths occur from the same general disease syndrome and around the same time, within a few days then gross necropsy should be done on several 3 or
more fresh carcasses to try and establish cause of death.
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If the same syndrome continues to be associated with deaths over subsequent days, then additional gross necropsies can be conducted on fewer representative animals one
or two animals per day in order to confirm the gross cause of death. If animals die with different signs or if initial gross necropsy does not identify a cause of
death, then a more comprehensive necropsy may be conducted in an attempt to identify the cause.
Digital images of standard views at necropsy and of any lesions provide an option that may allow peer review at a later date and discussion of possible explanations and
classification into causes. If there are concerns that deaths may be occurring with signalment, signs or gross
necropsy changes that are inconsistent with the recognised major causes of death, then consideration should be given to further investigation including preparation on the same
or subsequent voyages for collection of biological samples that can be imported back into Australia for examination by veterinary pathologists.
It is suggested that consideration be given to incorporating the use of a targeted or simplified gross necropsy protocol into future revisions of the Veterinary handbook for the live export
industry.
12.3 Pathogens associated with respiratory disease
