This is the first clinical trial, to the authors' knowledge, to demonstrate recovery from chronic footrot and its associated lameness. The rapid time to recovery with parenteral antibacterials is remarkable given that these sheep had been lame from 28 days to two years. It does highlight that systemic treatment with 12 days of therapeutic level of antibacterials is highly effective against this bacterial disease, even for chronic lesions where sheep have a persistent footrot lesion with hyperplasia and misshapen hoof horn [3
]. Although sheep with chronic lesions recovered from lameness and had no active footrot lesion in the current study, we do not know whether or when feet with hyperplastic horn returned to normal physical conformation. Hoof horn damage takes several months to resolve [3
] and the follow up period for the current trial was only 28 days, hence no information could be collected on improvement in physical conformation. There is evidence that sheep with poor foot shape are more likely to improve their foot quality after treatment with parenteral antibacterials [17
There were no time parallel controls in the trial with sheep with chronic footrot, instead, sheep acted as their own control in a pre and post quasi experimental design. These sheep had been lame for such a long time and given local treatments so it seemed unethical to not give these sheep the parenteral antibacterials that are the best known treatment for footrot [10
]. Quasi experimental designs are widely used in medical and social research where it is unethical to either withhold a treatment that has known efficacy or where there is a need to intervene quickly e.g. to prevent spread of infectious disease [14
]. There is a possibility of confounding by factors that could have been different between the two time periods (pre and post treatment) such as climate. Climate has been shown to influence both the severity and spread of footrot [3
]. However, given that there was a wide range of time in the duration of lameness it is highly unlikely that recovery after treatment with antibacterials occurred for any other reason than the treatment given.
In Kashmir, there are many challenges faced by farmers in managing footrot. Due to practical constraints, sheep that develop footrot whilst on Himalayan pastures are not treated until they return to the valley. They walk a substantial distance to return home, usually on hard roads that thicken and harden the hoof horn. Once home, lame sheep are typically treated as described in the introduction. Parenteral antibacterials are generally not used; farmers have been told they are ineffective and there are always concerns about the price and quality of pharmaceuticals (authors, personal communication). The results from the current trial indicate that if farmers use a course of four long acting injections of a relatively inexpensive well sourced antibacterial, there will be welfare benefits to the sheep and economic gain to the owners because once they are not lame and in pain [18
] these sheep will gain body condition and have improved conception rates and lambing percentages [11
]. There are sheep both in India and other countries with chronic footrot--either through neglect or inappropriate treatment. There is every reason to consider that the treatment presented in the current study would be effective in resolving footrot in these sheep.
As importantly, sheep with acute footrot recovered in a median 7 days after treatment with antibacterials, similar to other studies [10
]. However, sheep that received the traditional treatment of topical potassium permanganate solution were lame for longer with only 4 recovering within 28 days suggesting that this is an ineffective treatment. A solution of potassium permanganate is generally made at home by using the crystals that are readily available and cheap (authors' personal communications). Its use is common in these communities to disinfect water and as a general antiseptic for human skin conditions at concentration of 0.01% [19
]. Factors such as the deep seated location of D. nodous
in footrot lesions [3
] and/or an incorrect concentration of the solution could have contributed to low cure rates. It is possible that for very mild cases of interdigital dermatitis topical application leads to recovery. The lesions that received topical treatment in the current study ranged from moderate interdigital damage to some separation. There was no information collected on the strength of solution used by the farmers.
There was no significant difference between long acting oxytetracycline and enrofloxacin on time to recovery from footrot in the current trial. Enrofloxacin is a third generation fluoroquinolone, a broad-spectrum bactericidal antibacterial that is commonly used in veterinary and human medicine in India [20
]. It was used in the current trial because of its common use and accessibility in India. Given the global concern with the development of antibacterial resistance with flouroquinolones [21
] and the fact that the long acting oxytetracycline was equally effective, we consider that long acting oxytetracycline, which is rarely used in human medicine, should be used to treat sheep with acute or chronic footrot in India.
In the current trial, sheep were followed for up to 10 days after recovery or a maximum of 28 days after treatment. No sheep treated with parenteral antibacterials became lame again during this period; however, we do not know whether footrot recurred after the end of the trial. Sheep with acute footrot with damaged feet and poor foot integrity are more likely to get footrot again, although this is less likely if they have been given parenteral antibacterials [17
There was a significant association between lesion severity and time to recovery from footrot in both acute and chronic cases, with severe lesions with extensive interdigital dermatitis and separation of horn taking longer to heal. This is in contrast to other trials [9
] which reported no link between severity of lesions and time to recovery. However, in Kaler et al. [10
] and Jordan et al. [9
] the majority of the sheep (> 94%) had the most severe lesion score (score 4), in addition, Kaler et al. [10
] used a different system to classify lesion severity which might have affected the results obtained.
Sheep in the current trial were scored by three trained observers (with one observer making all the observations per farm); this could have led to some observer bias. However, the same observer was used to score all the sheep and follow up observations to minimize observer variability. Unlike sheep with acute lesions where there was no difference in recovery by farm, sheep with chronic lesions had a significantly shorter time to recovery on two farms compared with the other three farms. The sheep on each of these farms were scored by two different observers. The fact that these observers also scored acute cases and that there was no differences in time to recovery by farm suggests that this is less likely to be observer bias unless observers were only biased when scoring recovery from chronic lesions. Sheep on these two farms had lesion score severities 3 and 4 and duration of lameness from 3 months to 2 years which suggests the rapid recovery was unlikely to be a confounding effect of severity of footrot or duration of lameness. There is a possibility that the treated chronic cases on these two farms had better foot integrity than other farms which led to rapid recovery [3
], however, no information on foot integrity was recorded in this trial to investigate this.