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Local disease watch - April 2016

Fungal disease affects cattle.

Facial eczema has been confirmed in dairy cattle on the Far South Coast. Liver failure caused by eating the toxin of a fungus in dead grass leads to photosensitization. Areas of white and unpigmented skin attract sunlight, before peeling and sloughing. Some of the cattle involved in the Bega area outbreaks have died, and production of a large number of milking cows has been significantly reduced. Spores of the fungus are found in dead grass pasture litter. The recent outbreaks have involved ryegrass and native pastures, although any dead pasture litter could harbour spores. Pasture topping contributes to the amount of dead litter on the ground. Warm, moist weather aids multiplication of the fungus. Spore counts are used to determine the risk of pastures, and the high spore counts on the affected Bega farms have broken records. Facial eczema has previously affected alpacas on the Southern Highlands.

Once is not enough

Seven calves recently died from blackleg on a south coast farm. Blackleg is a bacterial infection which causes sudden deaths in young cattle. The spores of blackleg bacteria are present on most farms, however outbreaks of disease occur in coastal areas. Multicomponent vaccines that provide very effective protection against blackleg have been available for decades. All these vaccines require two doses to be given, four to six weeks apart. It is easy to forget to give stock their booster vaccination, but the omission can be disastrous.

Barber’s pole worms

Extended hot, dry conditions have slowed the barber's pole problem in tablelands sheep, but only for the time being. This weather prevents hatching of worm eggs, and kills worm larvae already on pasture. However, recent worm egg counts in some mobs are well into the thousands of eggs per gram, all barber's pole. And these worms will still be pumping out worm eggs when autumn arrives. Several producers say they have a problem with barber's pole for the first time this year, so don't become too complacent. It will be warm enough for barber's pole worm eggs to hatch for another month, if we get rain. Any larvae that develop will be able to survive right through winter. So it is important to do a worm egg count and worm type now, to know what you're dealing with.

Liver fluke

An autopsy on a 40kg crossbred lamb on the Tablelands showed immature liver fluke. The owner hadn't seen liver fluke on this property for some years. Liver fluke in cattle has been on the increase in the district, and we've been expecting levels in sheep to follow suit. This lamb had been on typical "flukey" country (paddocks with a spring, swamp or creek) for only a short time, and its liver was peppered with holes and the belly was full of protein-rich fluid. It takes about three months following fluke pick-up before eggs appear in faeces, so a fluke test on faeces during this time will miss the infection. A blood test is better. If you have had liver fluke on the property in the past, but haven't needed to fluke drench for several years, it would be worth testing sheep running in suspect paddocks.

Blue-green algae

Toxic algal blooms have developed on many farm dams and watercourses, encouraged by warm temperatures and lack of run-off. Organic matter such as decaying grass or animal faeces, and high nutrient levels especially nitrogen and phosphorus, support algal growth. Two main species are associated with poisoning in livestock. A thick floating green scum is common, although the water may appear discoloured without a floating scum. Wind pushes the scum towards the edge of a dam, and stock avoid drinking from scum-covered areas, if they can.

While the toxicity of algae is highly variable, it is safer to consider that it is toxic until proven otherwise. Poisoning is likely if the scum or discolouration covers the whole dam, such as on a calm day, or where fencing prevents access to clear water. Blue-green algae causes liver damage, leading to sudden death, or death within a day or so after developing abdominal pain and jaundice. Occasionally, nervous signs including tremors, blindness, aggression and convulsions are seen prior to death. Surviving animals may develop photosensitisation. Handle algal blooms carefully, as some people develop severe dermatitis.

Water drawn from below the scum and pumped to troughs is usually safe, but watch for algal build-up in any trough or open tank. Water treatment to remove the algae includes aeration such as tethering an outboard motor or spraying water into the air, or adding barley straw which may take a couple of weeks to work. Use of algaecides including copper sulphate which itself may cause livestock deaths, or the triazine herbicide simazine are not recommended. Beware that when algae die, toxin is released into the water.

Bill Johnson
District Veterinarian
Bill.Johnson@lls.nsw.gov.au