Limping Sheep Strike Fear in Shepherds

By Jane Fyksen, Crops Editor
Thursday, February 22, 2007 11:44 AM CST

Donna Onstott

First in two-part series

Ask Wisconsin sheep producers what's the one sheep-health problem they fear the most.

The likely answer is footrot. Nothing strikes fear into the hearts of shepherds like a couple limping sheep.

Footrot and other infectious foot problems were recently the focus of Donna Onstott, a veterinarian and Dresser sheep producer. She spoke at the Indianhead Sheep Breeders Association's Shepherd's Clinic in Rice Lake.

Onstott has both a veterinary degree and a doctorate in zoology from the University of Minnesota. She's worked with small-ruminant clients in private practice and also in industrial veterinary medicine caring for sheep used in biomedical device research. She owns a flock of 100 commercial polypay ewes and crosses some with Suffolk for fast-growing market lambs. Onstott also serves on the planning committee for the Miracle of Birth Center at the Minnesota State Fair.

While footrot isn't "common" per se, it can be "devastating" to the producer unfortunate enough to acquire it in his flock.

Though footrot is the most "infamous" infectious disease of feet in sheep, there are other ones, too - toe abscesses, interdigital dermatitis (or foot scald) and foot (i.e. heel) abscesses. All have bacterial causes, involve only the feet and require similar conditions for infection and spread. Onstott notes that foot scald can predispose sheep to more serious foot infections, and abscesses can result in "severe" lameness. Both might be mistaken for footrot, she warns.

All four of these foot diseases decrease a flock's productivity, and they can create animal welfare issues, notes Onstott.

Onstott says "management" is important in their prevention (and treatment). "Prevention is better than cure," she stresses.

Taking a look first at toe abscess (also known as white line abscess or septic laminitis), Onstott describes it as an infection of sensitive tissues (laminae) under the hard horn of the toe (or outer wall). It most commonly shows up as sudden lameness in one foot, usually a front foot and one claw. It may or may not be visible externally. The claw, however, is "hot" and painful if squeezed; the sheep will "jump."

The bacteria that cause toe abscess vary, and they're found in the environment. The bacteria enter via small cracks in the horn or through areas of separation between the wall and sole (i.e. "white line"). A producer may see pus at the white line near the toe. However, you may have to pare the sole some to see the abscess. The tract may extend up to the coronet, which may be swollen or discharging pus, too, she notes.

Predisposing factors for toe abscess are anything that causes damage to the integrity of the horn, be it laminitis (from perhaps "grain overload"), overgrown hoofs impacted with mud, wet and abrasive conditions in the barnyard or sharp objects (like stones or overgrown stubble) on the ground in your pastures.

Toe abscess can usually be treated by paring back the foot to expose the abscess and allowing it to drain. Don't over-pare, Onstott warns, noting that you can also use an injectable antibiotic if draining alone won't take care of it. Penicillin is often sufficient, she says.

Interdigital Dermatitis - more commonly called "foot scald" - is an infection of the skin between a sheep's toes. It's a relatively mild condition by itself, causing "mild" lameness. The problem is foot scald can affect more than one foot - and a large proportion of a flock.

Several types of bacteria may be involved with Fusobacterium necrophorum the most important one. It's in the environment, as well as normally present in the gastrointestinal tracts of sheep. In other words, producers can't get rid of the organism on their farms so they'll need to change their management if they're seeing foot scald in their flock. As noted, foot scald predisposes sheep to more serious infections. It is in fact the most common precursor to that much-dreaded footrot.

A normal healthy foot has pale pink skin between the claws. There's no reddening, hair loss or discharge. There's also intact horn on the sole.

With a mild case of scald, the shepherd will see reddening, clear discharge and mild swelling between the toes. There also may be a whitish film of dead material. In more severe cases, there'll be erosion and ulceration of the skin.

Onstott warns against any conditions that soften or abrade interdigital skin, such as well long pasture, muddy paddocks and congregating areas, wet bedding in warm barns and grazing in stiff stubble. Don't keep sheep in such conditions for long periods, if possible, she says of foot scald prevention.

To treat mild cases, remove the sheep to an area of dry hard ground for one day, and then onto a less muddy wet area.

For more severe cases of scald, if you have only a small number of sheep, clean their feet and apply topical spray (zinc sulfate or tetracycline). If your flock is too large to handle that way, put them in a foot soak (where they stand in the foot bath) or run them through a foot bath (positioned in an alleyway or chute). Use zinc sulfate. How often you do this depends on how bad their environment is; Onstott recommends every 5 to 14 days. Keep the sheep in a dry area until the liquid has dried on their feet - about an hour, she says.

The third major infectious foot disease of sheep is foot abscess, otherwise known as heel abscess, bulbar necrosis or "bumblefoot." It's an acute infection of the deep tissues of the foot. The affected claw is very painful, hot, swollen and may splay outward.

Suspect foot abscess if you see sudden severe lameness in one foot. It may be non-weight-bearing, too; the sheep may hold it up off the ground. Foot abscess is most common in back feet. Heavy sheep are most susceptible, notes Onstott of heavily pregnant ewes or other sheep that might simply be overly fed.

With a foot abscess you'll see discharge of pus at the coronary band and sometimes between the claws. It usually develops as a complication of interdigital dematitis (scald) and sometimes after penetration of interdigital tissues by sharp objects in the environment. With foot abscess, deeper tissues are invaded by one of two species of bacteria - Fusobacterium necrophorum or Arcanobacter pyogenes.

A foot abscess can even spread to the bottom joint of the foot and rupture supporting ligaments, notes Onstott of just how crippling it can be.

Predisposing factors for foot abscess are damage to the interdigital space from wet pastures and mud (like with scald), stiff stubble and crusted ice in the winter and sharp stones and metal objects. Again, Onstott reminds that heavy animals - pregnant ewes in late gestation and big rams - are more susceptible to foot abscess.

"If caught early, penicillin may prevent joint infection," notes this vet. If the joint is involved, she says it may help to support the joint with bandages and treat with injectable antibiotics like penicillin, florfenicol (Nuflor) or ceftiofur (Naxcel or Excenel).

A sheep that's suffered a foot abscess may walk fairly well in a couple months, but there'll be permanent deformity. She adds that amputating the claw may be a last-ditch measure to "salvage" the sheep.

Editor's Note: Next week Onstott tackles the last - but certainly not the least - of the four infectious foot problems in sheep: Footrot.

Comments »

Comment on this story

Comments will be approved within 48 hours

Name:

Email: (optional)

Comments:

Image Verification: (Case sensitive)