An outbreak of severe iodine-deficiency goitre in a sheep flock in north-east Victoria.

BACKGROUND: Several outbreaks of goitre, considered to be related to iodine deficiency, occurred in sheep flocks throughout Victoria in 2010. OBJECTIVE: We describe one outbreak in Merino-Border Leicester-cross ewes and their lambs in north-east Victoria that appeared to be associated with increased rainfall and pasture growth, particularly during the preceding summer and autumn. RESULTS: The outbreak was characterised by a four-fold increase in neonatal lamb deaths and goitre, alopecia and poor skeletal development in the lambs. Most cases occurred in lambs born to 2-year-old crossbred ewes that had grazed long, lush perennial pastures throughout their entire pregnancy, whereas few cases occurred in mature crossbred or Merino ewes that had grazed shorter, annual pastures on hill country for 3 weeks in late pregnancy but were otherwise managed similarly. CONCLUSION: Existing recommendations for south-eastern Australia are that only spring-lambing ewes in iodine-deficient areas require iodine supplementation to prevent goitre in years with high autumn-winter rainfall. Aspects of this outbreak suggest that ewes lambing at other times of the year and grazing abundant pasture for prolonged periods may also require supplementation to prevent goitre, even if autumn-winter rainfall does not exceed previously established thresholds.

Financial effect of bovine Johne's disease in beef cattle herds in Australia.

OBJECTIVE: To assess the financial effect of programs for controlling bovine Johne's disease (BJD) in beef herds. DESIGN: A spreadsheet simulation model of a self-replacing beef herd in south-eastern Australia selling 400-kg steers at 15 months old. METHODS: The model calculated the monthly cash flow, and net present value (NPV) of cumulative cash flow, over 10 years. Four main control options were compared: (1) a base herd (no action to control the disease), (2) test and cull, and (3) partial and (4) total destocking. It was assumed that BJD was eradicated after 3 and 5 years with total and partial destocking, respectively, and not eradicated with a test and cull program. Scenarios were compared for both commercial and stud enterprises. RESULTS: If there was no discount on the sale price of cattle in commercial herds, deaths from BJD had to exceed 5% before the NPV of partial or total destocking was similar to taking no action to control the disease over a 10-year period. When cattle sales incurred a 10% discount, deaths had to exceed 1% before the destocking strategies would break even after 10 years. CONCLUSION: Control options for BJD should be carefully planned on an individual herd basis, as significant production and financial risks accompany destocking programs. Eradication will only be more profitable in the longer term, compared with living with the disease, when discounts on the sale of stock from infected herds are high. This can occur with the selling of store cattle or breeders. In stud herds, BJD will usually cause the total failure of the business.

Epidemiology of bovine Johne's disease (BJD) in beef cattle herds in Australia.

OBJECTIVE: To describe the epidemiology of bovine Johne's disease (BJD) in beef herds in Australia. DESIGN: Retrospective survey of beef herds detected with BJD between 1991 and 2006. METHODS: Information about the management and physical characteristics of affected herds, index and clinical cases, testing and control programs, and attitudes to BJD were collated from existing data and personal interviews of herd owners or managers. Herds were excluded if they contained fewer than 30 breeding cows or operated as a dairy farm. RESULTS: Records from 109 herds demonstrated the first detected ('index') case was 3.4-fold more likely to be a beef rather than dairy breed. However, further analysis revealed association with dairy cattle was an important risk factor for introducing BJD. Index cases were most likely detected by veterinarians investigating clinical cases of scouring or ill-thrifty animals during winter, particularly bulls or aged cows. Most herds with clinical BJD had only a single case, with only one high prevalence herd detected in the survey group. Over the period of observation, test and cull programs did not eradicate BJD unless combined with culling of known high-risk animals, but removal of high-risk cattle by partial or total destocking generally restored the trading status of affected herds. CONCLUSION: Excluding cattle with dairy contact from beef herds, ensuring more effective farm biosecurity, promptly seeking veterinary advice regarding scouring cattle and sourcing replacement cattle from demonstrably low-risk herds, such as CattleMAP and 'Beef Only' herds, are simple strategies that should reduce the risk of introducing BJD infection into beef herds.