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Local disease watch - March 2016

Livestock and their owners are constantly challenged by seasonal conditions. This month, a number of problems occurred on farms in response to summer rainfall. In addition, some valuable tips were learnt on worm control in cattle, and a warning given about treating backyard chooks.

Pulpy kidney kills sheep

Vaccines to combat diseases caused by some members of the clostridium family of bacteria have been available for more than half a century. These are widely used in sheep, goats and cattle to protect them against tetanus, blackleg, black disease, pulpy kidney and malignant oedema. The vaccines are sold under a number of product names, and frequently incorporate additives to protect against other diseases such as leptospirosis or cheesy gland, or worms.

It is surprising but not unusual that we still see cases on these easily preventable fatal diseases. Pulpy kidney is a disease of plenty, as outbreaks accompany a change in diet to more abundant high quality feed. Recently, about fifteen crossbred lambs died suddenly from enterotoxaemia (or pulpy kidney) on one property when the mob was moved from an almost bare paddock to a lush green pasture which had responded to recent rain. The animals usually die with few signs of a struggle. The carcases of affected animals swell after death and quickly start to decompose. On a second property, merino lambs died without being moved, but again January rain had freshened the pasture they were grazing.

The producer in the second case had made a very common omission. To be effective, these clostridial vaccines require two initial doses given four to six weeks apart. All too frequently, young animals get their first dose of vaccine at marking time, but never get the essential second dose.

The producer in the first case had given both initial doses, about six months ago. But the change in diet was so dramatic that the vaccination immunity was overwhelmed. This problem is more often seen in cattle, where several manufacturers recommend giving another booster vaccination after three months, prior to changing to good feed (fodder crop, pasture or supplements).

Worms in sheep and goats

With monthly rainfall for January more than twice the long-term average, and distributed pretty evenly over the month, barber's pole worms were again a problem. Egg counts rose dramatically from near nothing to tens of thousands in the space of a few weeks, mainly in younger-aged mobs. But even at this level, producers said the sheep with the high egg counts were "jumping out of their skins", or had "travelled a couple of k's to the yards without knocking up". At the same time, though, we've seen some producers caught out by barber's pole worms, with several weaners on one property and older ewes on another dying after a fatal encounter. Regular worm testing can provide a valuable early warning when conditions favour rapid worm build-up.

Part of the challenge with barber's pole in our district is its unpredictability. Not only is it not found on every property, but only certain paddocks on affected properties appear to cause trouble. Most of us select the paddock with the most "green" to run our weaners during summer and autumn. This is also the environment that best suits barber's pole. So this mob is usually the best one to sample to see if barber's pole is present on your property.

Barber's pole worms thrive with set-stocking too, placing rams at high risk on most farms. Rams tend to be shut in a small, secure paddock out of the way, where barber's pole can go unnoticed.

But not all worms in sheep at present are barber's pole. In a couple of mobs of weaners, a number of the lighter lambs started scouring due to thin-necked intestinal worm (nematodirus). This worm responds quickly to rain after a dry spell, especially where the same weaner paddock is used each year. And egg counts on several properties are showing an increase in black scour and brown stomach worms, not to the point of causing scouring, but at levels that mean a second summer drench will be needed.

Blind sheep

Several sheep were noticed stumbling into fences and running into trees when they were being moved. The most common cause of this blindness in sheep, cattle and goats is an infectious conjunctivitis known by the descriptive name of “pinkeye”. Animals with pinkeye start with a bluish discoloration of the clear part of the eye and a stream of tears down the face. But when these young sheep were examined, they had no obvious changes to the eye at all, apart from fixed dilated pupils. The owner reported that he had used a drench containing the chemical closantel about a week previously. This chemical causes permanent blindness in sheep or goats which are over-dosed at drenching time. The case highlights the importance of weighing animals prior to drenching, checking that drenching equipment delivers the correct dose, and that animals only get a single dose.

Not food poisoning, but poisoned food

A large number of chooks died on a local farm. The owner had been attempting to treat the poultry flock for a few weeks, without knowing what the disease was, before seeking help from a vet. Not only had the chooks continued to die, but some of the drugs the owner had been using are banned from use in poultry flocks.

The use of some antibiotics has been restricted or banned in food-producing animals, to preserve the effectiveness of those antibiotics for human use. Studies have linked the use of particular antibiotics in food animals to widespread antibiotic resistance in people. Antibiotics and other chemicals are also restricted in their animal use because residues in food are dangerous to people eating those animal products.

Backyard poultry flocks are sometimes treated with drugs obtained for caged birds, ignoring the label statement “Not for use in birds which are producing or may in the future produce eggs for human consumption”. This is a dangerous practice, risking the health of anyone who eats eggs from treated birds. It is also illegal.

Cattle producers wage 'War on Worms'

A series of five worm control seminars concluded with more than eighty cattle producers gathering at Braidwood and Murrumbateman in February. This followed similar seminars in Bega, Milton and Berry. Stephen Love, NSW DPI parasite specialist, presented the latest information on cattle worm control to an enthusiastic audience, supported by LLS District Veterinarians and representatives from drench manufacturers.

Topics included recognising the signs, laboratory tests used to diagnose worms, and combining management and drenches for sustainable worm control. Some of the messages to come out of the seminar were that a lot of drench is wasted by drenching cattle over two years of age for worms, whereas poor worm control in weaners and yearlings is a frequent cause of slow growth. Indications are that drench resistance in cattle worms is on the increase, and measures to provide young cattle with access to low-worm pastures after drenching reduces our reliance on chemicals for worm control. Alternate grazing with sheep, or grazing with adult cattle only, reduce worm contamination of cattle pastures, as do using crops or spelling. Drench resistance may be delayed by using combinations of chemicals concurrently, and selecting short-acting drenches followed by a move to low-worm pasture for optimal worm control. Not all properties nor all paddocks on a property have a liver fluke problem, with a regular blood test program for fluke the best way to establish its extent.

There have also been comparisons which confirm that the same drug given by mouth is more effective than when given either by injection or as a pour-on, but use of any drench must take into account facilities available, target parasites (worms, fluke or lice), experience and skills of the operator, and worker safety.

Some of the information is summarised in the Meat and Livestock Australia (MLA) publication The Cattle Parasite Atlas, available from the MLA website:

http://www.mla.com.au/Research-and-development/Animal-health-welfare-biosecurity/Parasites