Footrot is a common and serious bacterial infection affecting sheep hooves, causing significant pain and mobility issues. This article covers its identification, causes, management strategies, and broader implications for flock health.
Identifying Footrot
The most apparent sign of footrot in sheep is lameness, ranging from a slight limp to a complete reluctance to bear weight on the affected limb. Sheep with footrot may walk on their knees or appear to graze in this position to alleviate pressure on their hooves. As the condition progresses, the hoof itself undergoes visible changes.
Initially, the skin between the toes may appear inflamed, red, and moist, sometimes with a grey, pasty discharge and a foul odor. Over time, the bacterial infection causes the horn of the hoof to separate from the underlying sensitive tissues, starting between the digits and potentially extending to the sole, heel, and outer wall. In severe or chronic cases, the hoof can become gnarled and distorted.
Understanding the Causes
Footrot results from a synergistic interaction between two bacteria: Dichelobacter nodosus and Fusobacterium necrophorum. D. nodosus is the primary agent, producing enzymes that degrade hoof connective tissue, causing horn separation. F. necrophorum, found in manure-contaminated environments, often initiates the process by causing interdigital dermatitis (foot scald), creating an entry point for D. nodosus. While D. nodosus can survive in the environment for up to two weeks, it primarily persists within infected sheep hooves.
Environmental factors significantly influence footrot’s development and spread. Warm and moist conditions, such as wet pastures or muddy pens, create an ideal environment for the bacteria to thrive. Damaged skin between the toes, from rough terrain or minor abrasions, predisposes sheep to infection. The bacteria spread through direct contact between infected and healthy sheep, or indirectly via contaminated pasture, bedding, or shared equipment.
Strategies for Management
Managing footrot involves both treating affected animals and implementing preventive measures to protect the rest of the flock.
Treatment
Treatment often begins with careful foot inspection and gentle trimming to remove loose or diseased horn, exposing infected areas. Excessive trimming is generally not recommended as it can cause further damage. After trimming, topical antibiotic sprays, such as oxytetracycline, can be applied. Foot bathing is another common treatment, typically using solutions of 10% zinc sulfate or 5% formalin. Sheep stand in these solutions for 5 to 15 minutes, allowing antibacterial agents to penetrate the hoof. For more severe cases, systemic antibiotic injections, such as long-acting oxytetracycline or macrolides like tulathromycin, are highly effective, achieving high cure rates, often between 70-90%.
Prevention
Prevention relies on a multi-faceted approach to minimize the risk of infection. Regular hoof inspection helps identify early signs of footrot. Maintaining dry conditions in sheep housing and pastures is important, as moisture promotes bacterial growth and spread. Pasture rotation can help reduce the bacterial load in the environment by allowing contaminated areas to dry out.
Quarantining new animals for several weeks before introducing them to the main flock allows for observation and treatment of pre-existing infections, preventing disease introduction. Culling chronically infected sheep that do not respond to treatment helps remove persistent sources of infection. Vaccination against D. nodosus can also stimulate immunity and reduce footrot incidence and severity. These vaccines typically require an initial course of two doses, followed by annual boosters, and protect against specific strains. It is important to consult a veterinarian for severe cases or to develop a comprehensive flock health plan.
Broader Implications for Flock Health
Footrot extends its impact beyond individual animal discomfort, posing significant challenges to overall flock health and productivity. The lameness caused by footrot reduces a sheep’s ability to graze effectively, leading to decreased feed intake and weight loss. This translates into reduced growth rates in lambs and lower body condition in adult sheep.
The disease also negatively affects milk production in lactating ewes and can diminish wool quality due to stress and reduced mobility. Footrot increases management costs for farmers, including labor, treatments, and veterinary services. In severe instances, chronic pain and lameness can lead to reproductive issues and increased susceptibility to other conditions, such as flystrike. Addressing footrot is important for both the economic well-being of a sheep operation and maintaining high standards of animal welfare.