Summary
Foot abscess in sheep occurs only sporadically when wet environmental conditions prevent hooves from drying out for extended periods. Because of this irregular expression FA was considered as only a disease of medium economic importance in the most recent analysis of nationally important endemic sheep diseases. However in the high altitude, high rainfall Tablelands region of NSW, FA has been shown, particularly during 2010, to cause ewe and lamb deaths and serious financial loss, particularly in heavy crossbred meat sheep.
Consequently, in 2011 we conducted a two part study designed to i) determine whether supplementing pre-lambing ewes with iodine would reduce the prevalence of foot abscess, and ii) identify environmental and management risk factors associated with foot abscess expression amongst local producers.
The investigation into the impact of iodine was conducted because i) some local lamb producers were treating ewes with iodine following anecdotal reports that this was beneficial; ii) iodine treatment was reported to reduce FA in cattle, and iii) there was a need to scientifically determine whether iodine was of benefit in Tablelands sheep so that appropriate advice could be provided to local industry.
The investigation into risk factors associated with FA was conducted because i) there was little specific objective information available on risk factors for FA in high rainfall Tablelands region, and ii) producers were facing what appeared to be a second year of high FA prevalence.
Because of the sudden onset of dry conditions during winter and early spring of 2011, and the consequent reduction in the prevalence of FA, only 2% of the trial ewes developed FA over lambing and we were unable to adequately test the value of supplementing pregnant ewes with iodine for reducing the impact of FA. However, because there continues to exist a growing anecdotal belief amongst producers that iodine is beneficial for controlling FA it remains important to test this hypothesis. Given the sporadic nature of FA we propose to conduct a simplified low cost opportunistic trial that could be applied at short notice should the environmental conditions arise for FA expression. Several producers have already offered their flocks for this study.
The risk factor investigation comprised a cross-sectional, observational study of 115 producers in the Tablelands region of NSW by telephonic interview. Multivariable logistic regression analyses were performed to identify significant predictors of foot abscess presence and prevalence level after adjusting for potential confounders. Detrimental risk factors identified were moving sheep during lambing, having more than four months of wool growth at lambing, having any level of boggy areas within the paddock, a wet season, and having greater than 30% clover in the paddock. A favourable risk factor was having shale/slate soils. In terms of changed management producers should be prepared for an increased risk of FA when wet seasons are predicted, and consider lambing in the autumn, not moving sheep during lambing, moving shearing to within four months before lambing, running pregnant ewes in a paddocks with no higher than 30% clover, or containing boggy areas. However because most of the associations identified are not consistent with maximising productivity, management changes such as lambing earlier, lambing on paddocks of low fertility with low clover content, are likely to reduce lamb turnoff and reduce profitability. At best producers should be prepared for an increased risk of foot abscess when wet seasons are predicted. By being more vigilant in these periods and making sure that the precursor condition, interdigital dermatitis (OID), is absent or controlled, they may be able to reduce losses.
