'Staggers' in Sheep

E-mail contact Dr Ray Batey

Austbreed's veterinarians are contactable through: frontdesk@austbreed.com.au

or visit our website: http://www.austbreed.com.au

Acknowledgement: This article is based on more than 30 years of experience, but also relies on the definitive classification of these diseases presented in a review paper by Dr C A Bourke in the Australian Veterinary Journal of June 1995.

In the region serviced by our veterinary practice (south east of Perth, Western Australia), farmers tend to regard staggers as being due to white muscle disease (selenium deficiency), annual ryegrass toxicity or poisonous plants. However, there are many potential causes of incoordination in sheep, and it is important that these be distinguished when they occur, because it is possible to limit the losses from some of these conditions if they are diagnosed early.

Any disorder of the brain or spinal cord, of muscle, bone or joints, resulting in incoordination and a tendency for sheep to fall or become recumbent, is referred to as 'staggers'. This can manifest in a few individual animals or may be seen affecting a large proportion of a mob simultaneously or within a short time. Animals manifesting such signs may recover temporarily or permanently, or deaths may occur.

To adequately distinguish the possible cause, a veterinarian needs to examine affected animals (or be provided with an accurate description of behavior) and in many cases, a post mortem or other examination may also be required for definitive diagnosis.

Clinical appearance is an important distinguishing feature

Veterinarians examining affected animals are likely to use Bourke's five categories of clinical signs to assist with differentiating possible causes. The classification is relevant to early stages of the disease, and often relies on observing effects in a number of animals.

Limb weakness The hind limbs are affected in most animals with staggers, but muscles elsewhere in the body, or specific muscles or muscle groups, may also be involved. The signs may be due to an inability of muscles to contract properly as occurs in white muscle disease, or muscles may become rigid as in tetanus. The main effect is on locomotion.

• manifestations of selenium or vitamin E deficiency
• post shearing staggers or oxalate poisoning (hypocalcaemia) transit tetany or in lactating ewes on grass dominated pastures (hypomagnesaemia)
• plant poisoning such as by marshmallow
• genetic disorders including progressive muscular dystrophy of Merinos
• polyarthritis after dipping may also manifest in this way.

Limb weakness with knuckling of hocks, knees, and/or fetlocks Some of the conditions in this group manifest only with the main feature of knuckling and weakness:

• plant poisonings such as onion grass or Zamia palm
• copper deficiency
• specific chemical poisons
• Other conditions have various additional effects on the nervous system:
  • botulism
  • ivermectin poisoning
  • vitamin A deficiency
  • plant poisoning such as blind grass or morning glory
  • listeriosis (bacterial infection of the brain) which may follow dipping

Falling over / recumbency The most likely causes of this manifestation are genetic conditions affecting certain strains of fine and medium wool Merino sheep, or another condition in Poll Dorsets. (In western New South Wales, poisoning with the Darling Pea is a potential problem.)

Falling over with tremors This manifestation is mainly associated with plant or microbial toxins and occurs in:

• phalaris staggers
• perennial ryegrass toxicity
• ergotism on paspalum

Convulsions Animals may walk normally and suddenly convulse if driven; in other conditions, animals may be recumbent and convulse when disturbed. Important examples include:

• subacute enterotoxaemia (our experience is that this is becoming more common than the acute, sudden death form)
• polioencephalomalacia (acute thiamin deficiency) - a particular problem in goats, but we also see it in sheep with a high grain intake.
• annual ryegrass toxicity - a similar toxin also occurs on some other grasses
• fungal toxin on water-damaged wheat

IMPORTANTLY, SOME OF THESE CONDITIONS, IF DIAGNOSED EARLY, CAN BE TREATED OR MANAGED TO LIMIT LOSSES.

If 'staggers' are occurring in a sheep flock, early contact with a veterinarian is advisable. The appropriate management of these conditions depends on good communication and cooperation between farmer and vet. Even if an immediate investigation is not intended, we encourage clients to always contact us for initial advice.

What NOT to do

From our experience, recent examples of inadequate responses include:

• Believing that there must be plant toxins involved, a farmer waited almost 2 weeks, with the loss of thousands of dollars worth of prime lambs, before assistance was sought. Subacute enterotoxaemia was involved, and by the time a diagnosis was possible, it was too late to implement a control program.
• A client asked us to investigate the loss of sheep with staggers. Very little history was available, and to save on fees, the client brought a dead animal to our livestock facility for necropsy. The results were inconclusive and it wasn't until we actually saw affected animals some time later, that it was determined that botulism was involved. In the meantime losses continued.

What to do if sheep are seen with staggers: A good history is essential when making contact with a veterinarians.

• Observe what is occurring: How many are affected? Are the signs constant, or only when sheep are driven?
• Have the sheep been moved to a new paddock, or has there been a recent husbandry procedure?
• What has been happening with the weather, including rain and temperature?
• What is the feeding status- green or dry grass, or is there grain feeding?
• What age group is affected? If in lambs, is it associated with a particular sire?

Unless something is very obvious, DO NOT MAKE ASSUMPTIONS ABOUT THE CAUSE, and contact your veterinarian.