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CASE NOTES


FOOT ABSCESS IN TABLELANDS SHEEP: EVALUATION OF RISK FACTORS AND MANAGEMENT OPTIONS

Jeff Eppleston and Bruce Watt, Tablelands Livestock Health and Pest Authority, Bathurst, NSW and Navneet Dhand and Robert Barwell, Faculty of Veterinary Science, The University of Sydney, Camden, NSW

Abstract from the final report B.AHE.0073, Published by Meat & Livestock Australia Limited, NSW, July 2012.
The full report is available on the MLA website
Posted Flock & Herd August 2020

Abstract

Foot abscess occurs sporadically in sheep flocks depending on pasture conditions, but during the wet winter/spring of 2010 on the tablelands of NSW foot abscess was common resulting in considerable financial loss. 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.

In the iodine response trial, twin-bearing crossbred ewes from three flocks (N=900) were either treated with an iodine drench within two weeks of the start of lambing or were left untreated.

Every sheep had its feet inspected pre-lambing and at marking when foot lesions were recorded. During lambing, flocks were inspected weekly and lame ewes recorded. Pre-lambing, around 20% of the ewes had old foot abscess lesions and post-lambing, following a dry late winter period, only 1.9% of ewes had active foot abscess. There was no affect of iodine treatment.

For the risk factor trial we conducted a cross-sectional observational study involving 115 tablelands sheep flocks by telephonic interview. Multivariable logistic regression analyses were conducted using two outcome variables:
i) the presence of foot abscess, and
ii) low (<1%), medium (1% to 5%) or high (> 5%) levels of foot abscess.

We found that moving sheep during lambing, having more than four months of wool growth at lambing, having boggy areas within the paddock or a wet season, and having greater than 30% clover in the paddock were all associated with increased foot abscess expression. The findings from this study will be used to provide updated extension advice to producers.

Executive Summary

Foot abscess (FA) 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 Tableland regions, 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, and 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, ovine interdigital dermatitis (OID), is absent or controlled, they may be able to reduce losses.

Background

Foot abscess in sheep is an acute infection of the interphalangeal joint of the ovine foot with Arcanobacter pyogenes, usually following the development of interdigital dermatitis caused by Fusobacterium necrophorum which gains access to the skin following water maceration and mechanical damage caused by muddy wet pastures, particularly in heavy pregnant ewes and in rams (West et al., 2009). FA is a serious animal welfare issue and can drastically reduce animal productivity in affected animals. Overall the incidence of FA in Australian sheep flocks is usually sporadic and variable between years depending on pasture conditions. However in specialist lamb producing flocks joining heavy crossbred ewes, up to 15% of the flock may be affected.

Following observations of high ewe losses during 2010, the Tablelands LHPA conducted a survey of sheep producers with more than 1000 sheep to quantify losses and identify the main causes of ewe deaths (Watt et al., 2011). Mortality rates averaged 5.7% and 4.8% for adult and maiden ewes, respectively, but ranged from negligible to 28.6%. The most common causes of ewe deaths in descending order were: FA leading to pregnancy toxaemia; complications during parturition; and FA alone, suggesting that the costs associated with FA are very significant, given current sheep values.

Extension advice on the control of FA concentrates on avoiding risk factors such as over-fatness and wet, muddy-ground conditions (Allan, 2010). Other than these, little objective information is available about the risk factors for the disease. Knowledge of risk factors is essential for developing objective and science-based control programs and extension advice. As a result a major aim of this project was to utilise producers who had responded to the &quo;ewe loss&quo; survey to conduct a more detailed FA risk factor investigation.

In addition, anecdotal reports from local lamb producers suggested that treating ewes with an iodine drench prior to lambing can reduce the incidence of FA. This concept is supported by two reports in the scientific literature (Berg et al., 1984; Maas et al., 1984) of reduced foot infection in cattle treated with ethylenediamine dihydriodide (EDDI), an iodide salt. In these reports serum iodine concentrations were elevated 10-fold on Day 46 after the commencement of treatment and associated with this, the proportion of cattle with foot infections fell from 21% in untreated cattle to 8% in EDDI-treated cattle. A second objective of this project was to measure the effect of iodine supplementation on FA expression, including a literature review on the potential role of iodine on immune competence and FA expression.

 


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