Mitigating BRD risk in export livestock

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12.5 Mitigating BRD risk in export livestock

The live export cattle supply chain has many features in common with management of cattle in feedlots. This study suggests that the pathogenesis and epidemiology of BRD in live export cattle is likely to be similar to that in feedlot cattle. Therefore cattle selection and husbandry strategies used to prevent and control mortality in feedlot cattle are likely to also be effective in minimising the incidence and costs associated with morbidity and mortality due to BRD and other diseases in live export cattle. Prevention and control strategies aim to minimise pathogen exposure, stimulate herd immunity, and manage risk factors that potentiate the occurrence and severity of disease. 92 Mixing of cattle of unknown health status from different properties is an important risk factor for pathogen exposure and infection. The majority of cattle sent for export, particularly those on long-haul voyages, are sourced directly from their property of origin, so co-mingling at the assembly depot presents an important BRD risk. Risk mitigation strategies such as identifying cattle suppliers based on prior performance of cattle from that supplier, yard weaning, familiarity with feedlot feeding and watering practices and vaccination against prevalent major respiratory pathogens may have application in the export industry. The land-based feedlot industry has developed strategies for backgrounding cattle that incorporate some or all of these measures and that aim to maximise feedlot performance and minimise adverse health risks. It is recognised that applying interventions at the property requires advanced planning that may be problematic for either the land- based feedlot chain or the export chain. However, it is not defensible for the livestock industry to try and argue that risk mitigation measures are not feasible because of short lead times. The export industry has produced training material on low-stress animal handling of animals in the export chain and supports this with direct involvement in training and mentoring animal handlers in countries receiving Australian livestock by export. Many of these resources can be viewed on the LiveCorp publication pages. 93 It should be possible to develop systems that allow risk mitigation strategies to be developed as part of routine cattle supply preparations or to be encouraged and facilitated through preferential supply arrangements or regulatory compliance and QA benefits. Moving towards these strategies would require a strategic shift in the way the industry selects and manages animals prior to export and would reinforce that industry is committed to quality and performance. Vaccination can be used to stimulate individual and herd-level immunity. Vaccines are generally most effective if used in accordance with manufacturer guidelines and for many vaccines this may require two initial vaccine doses administered some weeks apart. This requires the same sort of planning as was discussed in the previous paragraph. More recent developments in BRD vaccines have focused on the development of single-shot vaccines that can be administered to cattle at induction. Some of these products are administered as an intra-nasal spray and can result in rapid onset of local immunity to 92 Perkins 2009; Edwards 2010 93 http:www.livecorp.com.aupublications Page 178 of 201 combat respiratory tract pathogen exposure and infection. In Australia there is now a one- shot vaccine registered for use in cattle to protect against M. haemolytica Bovi-Shield MH- One®. There are also registered vaccines in Australia for use in cattle to protect against BoHV-1, BVDV and there may be additional products used under limited licence for specific situations. In the USA and Canadian markets there are more diverse offerings of single shot beef cattle vaccine products that are directed against many of the recognised BRD pathogens. In fact one or more single-shot vaccine products can be identified in the USA or Canadian markets for all of the BRD pathogens studied in this project, with the exception of BoCV. The relevance of this is only to indicate that production of these vaccines is technically possible. Vaccines developed in other countries may not be appropriate for use in Australian cattle because of strain differences in pathogens and vaccines should not be used in Australian cattle unless there is evidence to support efficacy and safety. It is very important to understand that vaccination against BRD pathogens has been widely applied in feedlot cattle around the world and that impacts due to BRD morbidity and mortality continue to occur. Vaccination is not a panacea that will eliminate BRD risk in export cattle. Equivocal results in studies evaluating the impact of vaccination on BRD may be difficult to understand given that it seems intuitive that effective immunisation would be helpful. Possible reasons for failure to demonstrate beneficial impacts include variation in study design, timing of administration, failure of stressed animals to respond effectively to vaccine, and the complex causal web for BRD including the possibility of multiple infectious agents. 94 A recent systematic review of BRD vaccine efficacy against the M. haemolytica, H. somni and P. multocida concluded that there was evidence of benefit for vaccination against M. haemolytica and P. multocida, but no benefit from vaccination against H. somni. 95 In addition, there are strain variations for viruses and bacteria that may mean a vaccine available in one country may not necessarily be effective against the same pathogen in another country. Strain variation may even mean that a vaccine available in the same country is not always effective against the pathogens it is intended to combat, particularly if there is more than one strain in circulation. Mass medication has also been used as a strategy of mitigating risks for BRD in feedlots and in export cattle. There are distinctions between the administration of antibiotic to healthy animals on arrival called metaphylaxis and a decision in the face of a rapidly expanding epidemic of clinical cases of BRD to treat all animals in a group rather than identifying individual sick animals for treatment called mass medication. Metaphylaxis has been applied in some groups of cattle being prepared for live export in an attempt to reduce BRD occurrence and losses during export, most recently with a long-acting product containing tulathromycin Draxxin®. Concerns over metaphylaxis relate to cost, risk of antibiotic overuse and potential contribution to development of resistance and residues depending on product and time from treatment to slaughter. It is possible that use of metaphylaxis may mask other suboptimal management practices. 94 Taylor et al. 2010 95 Larson and Step 2012 Page 179 of 201 During the voyage, management of stocking rates, ventilation, bedding and other factors are based in part on management of risk to reduce morbidity and mortality risk from known problems including BRD. A large longitudinal project investigating BRD in Australian feedlot cattle has recently been completed under the direction of researchers from the University of Queensland. 96 The final report from this project is currently being completed. This report will be of great interest for the livestock export industry in understanding risk factors for BRD in Australian cattle and possible preventive measures that may able to be applied to cattle being prepared for export. The work has identified protective effects reduction in BRD risk in cattle vaccinated with Bovilis MH™ and Pestigard™, but the effects of vaccination alone were relatively small and not as significant as a range of other management factors. 97 The main management factors that were identified as potentially being able to mitigate BRD risk were related to mixing, moving and grouping of animals in the period prior to feedlot entry. 97 These findings reinforce the value in best practice principles for BRD risk mitigation that have been well described both in Australia and elsewhere and that rely on management factors such as reduction in stress, movements and mixing and ensuring animals have access to good quality water and feed. 98 There is growing understanding of the importance of stress 99 and associated factors such as distance travelled to a feedlot 100 and liveweight shrinkage during transport 101 in exacerbating occurrence and severity of BRD in feedlot cattle. It seems plausible that management and stress-related factors may be more important in BRD risk mitigation than vaccination status and regardless of whether vaccination is implemented against selected BRD pathogens, it will be important to adopt management strategies aimed at reducing risk as well. A number of specific associations were noted in the current report that are related to management factors for BRD risk mitigation. Pathogen exposure risk in assembly depots is likely to be increased with increased mixing of animals from multiple sources and mixing of new arrivals with carry-over animals. Our findings and those of Hick et al 102 have flagged the likely importance of BCoV as a viral agent involved in BRD and the circulation of BVDV in assembly depots and during the voyage, despite testing strategies aimed at removing infected animals pre-export. Any risk mitigation measure including vaccination should be carefully evaluated and applied only if demonstrated to have a beneficial effect through valid scientific studies. However, a lack of clear data does not mean that no measures should be adopted. Measures may be adopted where there is a reasonable expectation that they will mitigate risk, but in this situation there must be concurrent monitoring to assess impact and the ability to change risk mitigation measures if and when there is convincing evidence from valid scientific studies. 96 Condon 2013; Barnes et al. 2014; Hay 2014 97 More 2002; HayHay 2014 98 MLA 2006 99 Hodgson et al. 2012 100 Cernicchiaro et al. 2012 101 Cernicchiaro et al. 2012 102 Hick et al. 2012 Page 180 of 201 Targeting mitigation measures to those groups that have higher risk offers a cost effective means of reducing morbidity and mortality but requires clear justification for differential management and monitoring to document efficacy. Advances in technology and leveraging of health monitoring at the individual animal level in association with NLIS animal identification data offer an unparalleled opportunity for industry to collect data efficiently to allow monitoring of performance and assessment of efficacy of various management or treatment factors. See Section 12.10 for more detail.

12.6 Other causes of death