Sheep Health in Australia

The most productive sheep enterprises in Australia spend more on prevention than on treatment. This is not coincidence — it reflects a fundamental truth about animal health economics. The clostridial diseases that kill sheep without warning cost nothing to prevent with a $1 vaccine dose and everything to deal with after the fact. Anthelmintic resistance costs almost nothing to slow when managed strategically and an enormous amount in drench efficacy loss when it is not. Blowfly strike costs significantly less to prevent than to treat. The pattern is consistent: investment in systematic prevention returns far more than reactive treatment of the consequences.

Building a structured flock health program starts with a conversation with your local veterinarian, ideally before a problem arises rather than during one. A district veterinarian or private vet with small ruminant experience understands the specific disease pressures in your area — which clostridial diseases are most prevalent in your region, what drench resistance is already present in local worm populations, what the local mineral deficiency profile looks like, and what biosecurity risks exist from nearby properties. This local knowledge is more valuable than generic advice, and establishing the relationship before you need emergency assistance makes every health event on your property easier to manage.

The four pillars of preventive sheep health in Australia are: vaccination against clostridial diseases; strategic parasite management; biosecurity to prevent disease introduction; and nutritional health. These are addressed in detail in the sections that follow. Address all four consistently and the reactive health burden on your enterprise will be substantially lower than if any one is neglected.

Clostridial vaccination is the single non-negotiable in Australian sheep health. The clostridial diseases — enterotoxaemia, tetanus, blackleg, malignant oedema, and black disease — are fast-killing, universally fatal once clinical, and completely preventable with routine vaccination. Losing sheep to enterotoxaemia or tetanus in a vaccinated flock is rare to the point of unusual; losing them in an unvaccinated flock is a predictable outcome that will eventually occur.

5-in-1 vaccine is the minimum for Australian sheep — it covers Clostridium perfringens types B, C, and D (lamb dysentery, struck, and enterotoxaemia/pulpy kidney disease), Clostridium tetani (tetanus), and Clostridium novyi type B (black disease). The 6-in-1 adds Corynebacterium pseudotuberculosis (cheesy gland/caseous lymphadenitis — CLA). The 6-in-1 is recommended for most Australian sheep enterprises given the widespread prevalence of CLA and its significant production impact.

The vaccination protocol for unvaccinated adults requires two doses four to six weeks apart for the primary course, then annual boosters. For ewes, the booster should be given four to six weeks pre-lambing — this maximises the antibody concentration in colostrum, providing passive immunity to lambs for the critical first weeks of life. Lambs born to vaccinated ewes with passive immunity should receive their first vaccine at six to eight weeks and a second dose four weeks later. Lambs from unvaccinated ewes have no passive protection and should be vaccinated earlier — from two weeks of age — and are at higher risk in the gap before vaccine-induced immunity develops.

Enterotoxaemia (pulpy kidney disease) is the clostridial disease most likely to catch producers by surprise because it strikes the best animals — the fastest-growing lambs and the best-conditioned adults — rather than the weakest. It is caused by Clostridium perfringens type D, which proliferates explosively in the small intestine of animals consuming high quantities of rapidly fermentable starch. The trigger events are: access to grain, transition to lush spring pasture, and any abrupt increase in starch intake. Death is typically sudden, with no prior warning. On post-mortem, the kidneys have a characteristic softened, liquid appearance (hence "pulpy kidney"). Prevention is vaccination. Treatment of already-dead animals is, obviously, not possible.

Tetanus kills sheep through any wound that creates an anaerobic environment — castration, mulesing, drenching gun injuries, docking, shearing cuts, and foot rot lesions are all potential entry points for Clostridium tetani. Lambs at marking time (castration and tail docking) are at particularly high risk, and unvaccinated enterprises performing these procedures in spring will experience tetanus deaths. The passive immunity passed through colostrum from vaccinated ewes protects lambs through the critical marking period, which is one of the most important practical reasons to maintain the ewe vaccination program rigorously.

Footvax — the registered vaccine against virulent strains of Dichelobacter nodosus (foot rot) — is appropriate for enterprises with confirmed virulent foot rot and as part of a formal foot rot eradication program. It does not prevent foot scald (a different condition) and does not eliminate infection already established in the flock — it reduces new cases and the severity of existing infection while the eradication program runs. Footvax requires careful temperature storage and handling and a multi-dose protocol. Work with your vet to confirm strain coverage before investing in a vaccination program.

Internal parasites — primarily the gastrointestinal roundworms of the order Strongylida — are the most significant ongoing health threat in most Australian sheep enterprises and the area where management decisions have the greatest long-term consequences. Anthelmintic (drench) resistance is now severe and widespread in Australian sheep worm populations, and the practices that producers adopt today determine how much efficacy remains available to them in five to ten years' time. This is not a hypothetical future problem — it is a current production crisis on many Australian sheep properties.

The main species vary by region and season. Barber's pole worm (Haemonchus contortus) dominates in warmer, wetter conditions — high-rainfall coastal and tableland areas of Queensland, NSW, and Victoria, and wherever summer rainfall occurs in significant quantity. It is a blood-sucker that causes rapid, severe anaemia and can kill animals within days in heavy challenge. The brown stomach worm (Teladorsagia/Ostertagia circumcincta) is the primary species in cooler, southern Australia and causes gastritis and production loss rather than acute anaemia. The black scour worm (Trichostrongylus colubriformis) affects the small intestine and causes scouring (scours) and rapid weight loss. Most Australian sheep enterprises carry mixed infections of two or three species, with the dominant species varying by season.

Drench resistance exists in all four main drench classes — benzimidazoles (white/BZ), levamisole (clear), macrocyclic lactones (mectin/ML), and amino-acetonitriles (Zolvix, the newest class). Resistance to the BZ and levamisole classes is nearly universal in Haemonchus populations across most of eastern Australia; ML resistance is increasingly common and is now present at high frequency in many areas of Queensland and NSW. This means that in many flocks, one, two, or all three of the older drench classes provide less than 95% efficacy — the threshold below which resistance selection accelerates rapidly. Producers who are not testing their drench efficacy are likely treating with ineffective products and selecting strongly for resistant worm populations without knowing it.

Faecal Egg Count Reduction Test (FECRT) is the gold standard for assessing drench efficacy on your property. The test protocol: take pre-drench pooled faecal samples from twenty or more animals in the group to be treated; drench with a single identified product from one drench class; take post-drench samples from the same animals fourteen days later; count eggs in both samples. A product providing more than 95% reduction in egg count is considered effective; below 80% indicates significant resistance. Run the test for each drench class separately, on separate mobs, over consecutive years. The cost per test ($80 to $200 depending on the laboratory and number of samples) is one of the best investments available in sheep health management.

Refugia-based management is the most important conceptual shift in modern worm management. Refugia refers to the proportion of the worm population that is not exposed to drench at any treatment event — worms in animals not treated, eggs and larvae already on pasture, and worms in the arrested larval stage within the host. Maintaining an adequate refugia population dilutes resistant alleles in the overall worm population and slows the pace of resistance development. The practical implication is: never drench the whole mob. Leave the animals with the best clinical indicators (best FAMACHA scores, best body condition) untreated at every treatment event. This is counterintuitive for producers trained in the calendar-drenching model, but it is the scientifically established best practice for managing resistance and is now the recommendation of the Australian Drench Resistance Sheep Parasite Research Program.

WormBoss (wormboss.com.au) is the Australian sheep worm management decision support tool — a free, region-specific online resource that provides recommended management programs based on your location, rainfall zone, and flock type. It is well-maintained, science-based, and more practically useful than any brief summary. Bookmark it and use it as your reference for drench timing decisions.

Pasture management is the non-chemical parasite control tool that is most underutilised on Australian sheep properties. Larvae on pasture die off significantly during: the hot, dry Australian summer (larval survival on pasture drops dramatically when soil temperatures consistently exceed 35°C); rest periods of six weeks or more during cooler months; and after cattle or horses graze a paddock (these species do not sustain sheep worm species — a "leader-follower" system where cattle graze ahead of sheep substantially reduces larval challenge on the pasture the sheep subsequently graze). Incorporating these principles into a grazing rotation reduces the total worm challenge to the flock and reduces drench dependence — the logical response to an era of drench resistance.

Blowfly strike is the most acute welfare emergency in Australian sheep management. The primary species, Lucilia cuprina (the Australian sheep blowfly), is present across virtually all sheep-producing regions and is active whenever temperatures exceed approximately 12°C — meaning in northern Australia and the warmer coastal areas, risk is effectively year-round, and in temperate southern Australia the high-risk period runs from October through to April.

Understanding the lifecycle helps explain why early detection is so critical. A single female blowfly, attracted by the warmth, moisture, and odour of a susceptible site (a damp or daggy breech, a wound, fleece rot, a birth-related discharge, or a pizzle-stained ram), lays 200 to 300 eggs. In summer temperatures above 30°C, these eggs hatch to first-stage larvae in as little as 8 to 12 hours. By 24 hours, larval feeding has begun. By 48 to 72 hours, a visible wound has developed and tissue destruction is progressing. By 96 hours, an untreated animal is in systemic distress from wound toxins and secondary bacterial infection. From egg-laying to death can be as short as four to five days in severe cases and warm conditions.

The prevention strategy has multiple complementary layers:

Remove susceptibility: Crutch all wool sheep before the fly season and before lambing; control scouring and remove dags promptly; treat all wounds with appropriate antiseptic wound spray; and in rams, maintain pizzle hygiene. Animals that are wet, daggy, or wounded are the primary targets — keeping the mob clean dramatically reduces the proportion of animals at risk on any given day.

Chemical prevention: Backline pour-on insecticides (registered cyromazine, spinosad, synthetic pyrethroid, or organophosphate products) applied at the registered rate and frequency provide stated protection periods of six to sixteen weeks depending on the product. Apply to dry animals. Check withholding periods against your intended sale date and market access requirements. Apply before the fly season rather than after strike has occurred — prevention is more effective and cheaper than treatment. Note that resistance to the older chemical families (synthetic pyrethroids) is increasingly reported in L. cuprina populations across eastern Australia — rotate chemical families where possible and follow resistance management recommendations for the product being used.

Mulesing: Surgical removal of the breech wrinkle skin remains the most effective long-term prevention of breech strike in Merinos. The bare, tightly drawn skin that results from healing is significantly less likely to accumulate moisture and dags than the original wrinkled skin. Mulesing is controversial on animal welfare grounds and is subject to export market restrictions from some wool buyers who have committed to mulesed-wool-free supply chains. Producers need to make their own decision based on their enterprise, their markets, and their ability to manage strike through alternative means. There is active industry breeding work to select for plain-bodied, bare-breeched Merinos that are naturally strike-resistant — this is the long-term industry direction, but it will take multiple breeding generations to achieve at a commercial level.

Monitoring: During high-risk periods, check the mob daily. Early strike — a small fresh wound with only larvae present and no significant tissue destruction — is easily treated with wound spray and recovery is rapid. Late strike requires broad wound debridement, removal of all larvae (every single larva must be removed — any left behind will continue to feed), application of registered wound treatment products, systemic antibiotic treatment if infection is established, and supportive care. Any animal with neurological signs from advanced strike, or with deep wound excavation into healthy muscle, has a poor prognosis and euthanasia may be the welfare-appropriate decision.

Foot rot costs the Australian sheep industry an estimated $100 million annually in production loss and treatment costs. It is one of the most painful conditions affecting livestock — severely affected animals cannot walk normally, cannot graze adequately, and lose body condition rapidly. Despite this, foot rot management remains inconsistent across the Australian industry because effective management requires sustained effort and discipline over a full season rather than a single intervention.

The distinction between foot scald and virulent foot rot is clinically important. Foot scald is caused by Fusobacterium necrophorum acting alone and presents as inflammation and moisture between the claws without horn under-running and without the characteristic offensive odour of foot rot. It is painful and can cause significant lameness in wet conditions but does not spread between animals at the same rate as virulent foot rot and does not permanently damage hoof structure. Most cases respond to footbathing and dry conditions.

Virulent foot rot involves both F. necrophorum and virulent strains of Dichelobacter nodosus. The combination produces enzymes that digest the horn-skin junction and allow the bacteria to track under the hoof wall, separating horn from sensitive tissue and creating the characteristically foul-smelling, moist, white necrotic material that distinguishes virulent foot rot from scald. Virulent foot rot is highly contagious — it spreads through infected soil and direct contact — and can establish permanently in a flock. Carrier animals (sheep that carry the organism in their feet without obvious clinical signs) are the primary reservoir that perpetuates the disease through the flock and between paddocks.

An eradication program, when successful, is one of the most valuable production investments available to an affected enterprise. The program requires: identification and scoring of all affected animals; paring back of all affected hooves; footbathing of the entire mob through a zinc sulphate bath (10% solution, minimum five minutes contact time for treatment); antibiotic treatment of all clinically affected animals (long-acting oxytetracycline at the registered sheep dose); Footvax vaccination of all animals; strict quarantine — a minimum of six months without re-introduction of untreated animals; and follow-up examinations at one, two, and four months after initial treatment to identify and remove any remaining carriers. The program requires commitment over a full season but the production gain from a clean flock is permanent. Seek veterinary guidance before beginning — the details of execution significantly affect the success rate.

Ovine Johne's disease (OJD), caused by Mycobacterium avium subspecies paratuberculosis (MAP), is a significant production and biosecurity issue for Australian sheep producers. The disease has a long incubation period — typically two to five years between infection and clinical signs — which means that by the time animals are showing visible wasting, the infection has been present and spreading in the flock for years. This delayed presentation makes OJD one of the most insidious diseases in sheep management.

Clinical signs in sheep differ from cattle OJD — diarrhoea (the classic sign in cattle) is less consistent in sheep. Affected sheep typically show progressive wasting and ill-thrift, often despite apparently adequate nutrition and parasite management. They lose wool over the back, become increasingly separated from the mob, and develop soft swelling under the jaw (bottle jaw) from protein loss. Death follows over weeks to months. Animals typically begin showing clinical signs at two to four years of age.

The key management challenge is that there is no treatment for OJD and no practical method of eradicating it from an affected flock. Management options are: vaccination (Gudair, the registered sheep OJD vaccine, does not prevent infection but substantially reduces the rate of clinical disease and faecal shedding, and is the most practical management tool for infected flocks); testing and culling (removing positive animals identified by faecal PCR or post-mortem culture — effective at reducing prevalence but not achieving eradication from an infected flock); and biosecurity to prevent introduction to clean flocks.

Purchasing animals is the primary route of OJD introduction. Buy from OJD-Assurance Level flocks where possible, quarantine all purchases, and test high-value purchases individually before introduction to the main flock. OJD infection status should be a routine question when sourcing sheep from any source. The costs of introducing OJD to a previously clean flock — in terms of production loss, management disruption, and restrictions on movement of your animals — are substantial and long-lasting.

OJD is a notifiable disease in some jurisdictions and is covered by state and national control programs. Consult your state department of agriculture or your veterinarian for the current regulatory requirements and support programs in your area.

Pregnancy toxaemia (twin lamb disease) is the most common metabolic disease in Australian sheep and one of the most preventable. Understanding its cause, recognising its early signs, and intervening before it is advanced are the three skills that make the difference between occasional losses and significant mortality during lambing.

The condition develops when a ewe in late pregnancy — almost always carrying two or more foetuses — has insufficient energy intake to meet the combined demands of her own maintenance and the rapidly growing foetuses. The body responds by mobilising fat reserves, but when the liver's capacity to convert mobilised fat to glucose is exceeded, ketones accumulate in the blood (ketosis). As ketone levels rise, the ewe becomes progressively more obtunded, eventually developing neurological signs, and dies if untreated.

Risk factors are: carrying multiples (twins or triplets — singles are rarely affected); poor body condition (BCS below 2.5) entering the final six weeks of pregnancy; late-pregnancy nutrition below requirements; sudden reduction in feed intake (cold weather, pasture failure, mob stress); and obesity (BCS above 4 entering late pregnancy — fat ewes develop hepatic lipidosis in pregnancy toxaemia with a worse prognosis than thin ewes).

Early signs: a ewe that is quieter than usual, slightly off-feed, separating from the mob. At this stage, a handful of grain and a drench of 60 to 100ml propylene glycol twice daily can turn an early case around within 48 hours. Late signs: the ewe is obviously dull, unsteady on her feet, blind, grinding her teeth, and unable to maintain her normal posture. At this stage, intravenous glucose administration is needed (injectable 50% dextrose, under veterinary guidance), the prognosis is guarded, and caesarean section may be the best option to save the lambs even if the ewe does not survive. Any late-pregnancy ewe found dull, off-feed, or separated from the mob should be treated as a pregnancy toxaemia suspect and given propylene glycol immediately while you assess further.

Prevention is entirely nutritional: ensure late-pregnancy ewes meet their energy requirements through adequate high-quality feed. Draft ewes by scanning result and feed multiple-bearing ewes separately at higher rates than single-bearing ewes. Monitor body condition at pregnancy scanning and adjust rations for ewes below BCS 2.5. Do not make sudden feed changes in late pregnancy. These practices, consistently applied, reduce pregnancy toxaemia to a manageable rarity rather than a significant annual loss.

Biosecurity — preventing the introduction of new diseases through purchased animals, shared equipment, and other transmission pathways — is one of the most important management areas in Australian sheep production and one of the most inconsistently practised. The consequences of biosecurity failures can persist for decades: OJD, once established in a flock, is essentially permanent; virulent foot rot strains, once introduced, can take a full season of intensive management to eliminate; drench-resistant worm populations introduced on purchased animals persist in the environment indefinitely. Keeping diseases out is fundamentally easier and cheaper than managing them once established.

Purchased animals are the primary biosecurity risk. Before buying: request disease history and flock health status information from the vendor, including OJD assurance level, foot rot status, and drench efficacy history. Buy from registered studs or properties with documented health programs wherever possible. For high-value genetics purchases, consider individual animal testing (OJD faecal PCR, blood tests for specific diseases) before introduction.

Quarantine all new arrivals for a minimum of four weeks in a separate paddock with no contact with existing stock. Drench new animals on arrival with a combination drench product and perform a pre- and post-treatment faecal egg count to assess the worm population they are carrying. Treat for lice on arrival regardless of visual appearance. Footbath on entry if foot rot is a concern in your area. Check for signs of OJD wasting, respiratory disease, and other conditions during the quarantine period before releasing to the main flock.

Shared equipment is a consistently underestimated biosecurity risk. Foot trimming tools, shearing equipment, and marking/tagging equipment can transmit CLA, foot rot, and other pathogens between animals and between properties. Require contractors to clean and disinfect equipment before working on your property. Provide a disinfection station and confirm its use. Do not share drench guns between farms without disinfection — drenching guns that contact mouth and throat mucosa can theoretically transmit respiratory pathogens.

The Livestock Production Assurance (LPA) program, Australia's nationally recognised on-farm quality assurance program, provides a framework for biosecurity and farm management practices that is well-aligned with good sheep management. LPA accreditation is increasingly required by buyers and processors and is worth obtaining even if it is not yet mandatory for your markets — the documentation habits it encourages are good practice regardless of market requirements.