Footrot in Sheep: 2. Diagnosis

Note Number: AG0446
Published: August 2003
Updated: March 2009

The coloured sheet, Signs of Footrot should be attached to this Agriculture Note.

What to look for, the signs of footrot.

The signs of infection vary from mild reddening (inflammation) of the interdigital skin (skin between the digits or toes) to complete separation of the horn of the hoof.
Infection commences when bacteria lodge on the interdigital skin causing inflammation; the skin-horn junction then begins to erode and the horn starts to lift. From this point, the bacteria move under the horn causing separation of horn around the heel, sole, toe and eventually to the outer wall.

Sheep infected with footrot become progressively more lame and exhibit the following signs in progressive order:

1. Inflamed, red and moist skin between the digits.
2. A grey pasty scum between the digits.
3. Lifting of skin-horn junction between digits.
4. Under-running or separation of horn around heel, sole, toe and finally to the outside hoof wall.

Infected feet may also have a characteristic foul smell.

Factors affecting signs of footrot

The rate of spread of footrot through a flock, extent of under-running and speed of development of footrot signs in individual feet all depend on the four factors listed below. All must be considered in assessing any footrot outbreak;

• Environment - moisture and temperature in the pasture.
• Virulence of infecting bacteria.
• Type of sheep - Breed and soundness and shape of feet.
• Stocking rate and proportion of infected sheep.

After infection, the horn continues to grow and often encapsulates a pocket of infection inside the hoof. This makes detection difficult. New horn growth is often deformed by underlying infection and this provides a diagnostic sign.

During dry periods, the disease naturally regresses in a flock, lameness will decrease accordingly, but infection will survive in many feet. During dry times spread is absent, therefore interdigital signs are minimal.

The succulent nature of footrot affected feet attracts flystrike. Consequently flystruck feet and associated body strike are a common feature of footrot outbreaks. Severe pain and lameness are always associated with flystruck feet and this causes animal welfare problems.

Diagnosis

An accurate diagnosis is essential, as early outbreaks of footrot can be difficult to distinguish from other diseases. An early and precise diagnosis will assist in designing the best treatment program, reducing costs and avoiding treatment failures.

Many feet must be examined. Examining only one or two sheep can be misleading and may result in unnecessary or incorrect treatment. An assessment of virulence should also be made. This may require observing development of the infection in individually marked sheep over several weeks.

Animal Health Officers and veterinarians are able to confirm a diagnosis. They can also take samples which will enable a laboratory to confirm the presence and virulence of D. nodosus.

Scoring

To describe footrot at its various stages, a scoring system has been developed, the Modified Egerton Scoring System. In conjunction with the foot diagrams below (Figure 2) each stage is described, using the short description. The coloured photographs on the attached sheet have both the short and full descriptions.

0 - Normal foot. No lesion (sign of disease)

1 - A limited mild interdigital dermatitis (scald)

2 - More extensive interdigital dermatitis.

3 - Severe interdigital dermatitis and under-running of the horn of the heel and sole.

4 - Severe interdigital dermatitis and under-running of the horn of the heel and sole but with the under-running extending to the walls of the hoof.

Figure 2. The progressive stages and scores of footrot

Conditions similar to footrot

Diseases and conditions that can appear similar to footrot are:

• Foot abscess - usually only one foot affected with swelling and pus.
• Scabby mouth - affects skin above the hoof and has dark scabs.
• Shelly hoof (toe) - is a natural and dry separation of the outside of the hoof horn beside the toe. The resulting cavity may contain mud, faeces or stones and may become flystruck.
• Bruising - lameness in soft feet without other signs.
• Ovine Interdigital Dermatitis (OID) - inflammation of interdigital skin during warm wet weather. There is no under-run and OID heals quickly if feet are kept dry, such as overnight on battens. This condition is not uncommon, creates an ideal environment for footrot bacteria to infect, appears similar to the early stages of virulent footrot and is very similar to benign footrot.
• Strawberry footrot - scabs on skin at back of foot above the hoof, hot and swollen foot.

Further information

Footrot in Sheep - Agriculture Notes from DPI offices -

• AG0445: Footrot in sheep: 1. Disease facts
• AG0446: Footrot in sheep: 2. Diagnosis
• AG0447: Footrot in sheep: 3. Treatment
• AG0448: Footrot in sheep: 4. Prevention and damage control
• AG0190: Footrot in sheep: 5. Benign footrot

Beating Footrot - 39 pages, including colour photos, available from DPI offices.

Footrot the Facts - Video all about footrot, available on loan from DPI offices.

Acknowledgements

This Agnote was developed by Tom Glynn, August 2003.

It was reviewed by:

Tom Glynn, Farm Services Victoria. March 2009.