Why DAFWA carries out surveillance for livestock disease
Australia’s access to markets for livestock and livestock products depends on evidence from our surveillance systems that we are free of reportable and trade-sensitive livestock diseases. To gather this proof of freedom, the Department of Agriculture and Food, Western Australia (DAFWA) investigates cases where livestock show signs similar to reportable or trade-sensitive diseases. The WA livestock disease outlook – for producers (WALDO) is collated from information collected by DAFWA as part of proving Australia’s freedom from those diseases.
Recent significant cases submitted to the Animal Health Laboratories (AHL)
Case data from early January to early February 2015
Abortions in mixed-age dairy cows
- Abortion in mixed-aged dairy cows that appeared clinically normal was investigated in the South West.
- Over one week six cows aborted. All were in the second trimester of pregnancy.
- Blood samples were collected from the affected and other non-affected cows in the herd. Tissue samples were collected from the aborted calves and all were submitted for laboratory examination.
- Testing carried out for the reportable disease Brucella abortus as a cause of abortion was negative.
- Microscopic examination and testing confirmed Neospora caninum as the cause of the abortions.
- Of the 32 blood samples, 16 were positive for N. caninum, indicating widespread exposure within the herd.
- Dogs are the definitive hosts for the protozoan Neospora and they shed the infective stages. Foxes have never been implicated in the spread of this disease.
Ill-thrift in Merino ewe weaners
- Ill-thrift, weakness, diarrhoea and deaths were seen in 4–6-month-old Merino weaners in the Wheatbelt.
- In total, 30 weaners died and 70 weaners were affected from a mob of 700.
- The weaners were grazing canola stubble with ad lib lupins via feeders and were supplemented with hay.
- The weaners were vaccinated for pulpy kidney as lambs and received a booster when losses began.
- Blood samples, small intestinal swabs, fresh and fixed tissue samples and rumen content were all submitted for laboratory examination.
- Testing for annual ryegrass toxicity of rumen content and enterotoxaemia was negative, and intestinal worm egg counts and Salmonella cultures were negative.
- Following laboratory testing and bacterial culture, infection with Vibrio cholerae was diagnosed. The serogroup detected was not one associated with severe human cholera outbreaks.
- V. cholerae is an unusual finding in gastroenteritis cases in sheep in samples tested at AHL.
Neurological signs (sudden blindness) in Simmental bulls
- Cases of sudden-onset blindness were investigated in three one-year-old bulls in the South West.
- One bull died but two responded to treatments of thiamine and vitamin A.
- A range of tissue samples from the dead animal were submitted for laboratory testing.
- Microscopic examination of the brain showed severe polioencephalomalacia, most commonly caused by thiamine (vitamin B1) deficiency.
- Read more on thiamine deficiency induced polioencephomalacia (PEM) of cattle and sheep.
Downer cow and reluctance to stand
- A six-year-old Angus cow appeared nervous and was reluctant to stand.
- The cow was in the last trimester of pregnancy, and was found to have an inactive rumen and upper gastrointestinal system. Unfortunately the animal died during examination.
- Post-mortem revealed abundant contents and fluid in the rumen, but scant dry faeces in the lower gastrointestinal system.
- Apart from moderate changes in the liver, there were no other significant findings.
- A diagnosis of ‘vagus indigestion’ was made on the basis of history and post-mortem findings.
- Testing for transmissible spongiform encephalitis (TSE) was negative.
Testing animals in the correct age range with nervous signs for TSE and showing that they do not have the disease is a critical part of Australia’s proof of freedom from TSE. A recent diagnosis of bovine spongiform encephalopathy (BSE – mad cow disease) in Canada using similar methodology demonstrates the effectiveness of this form of surveillance.
In early autumn, be on the lookout for:
- Most common in intensively farmed livestock.
- Stress and high stocking density are common precursors to an outbreak.
- Causes profuse diarrhoea. Sheep may be found dead and pregnant ewes may abort.
- Read more on salmonellosis of sheep.
Ergot alkaloid poisoning (ergotism) in stock
- May occur if stock eat grain contaminated with ergot at greater than 0.02% by weight. (Ergots are part of a fungus that forms in seed heads, especially ryegrass.)
- Ergots may concentrate in the last 20% of silo grain so producers should recheck grain for the level of ergots when it is fed out.
- Common signs of ergotism in WA are heat stress and reduced production.
- Read more on ergots.
Grain overload, acidosis or grain poisoning in stock
- Affects cattle, sheep or goats being fed grain without a gradual introduction or after a sudden change to diet.
- Signs include depressed appearance, diarrhoea, bloating, rapid breathing, dehydration, lying down and deaths.
- Read more on grain overload, acidosis, or grain poisoning in stock.
Summer pneumonia in sheep
- Typically affects weaners and hoggets during late summer/autumn.
- More common in British breeds.
- Brought on by stressors such as entry to a feedlot, dust and cold stress.
- Acute signs include coughing, labored breathing, discharge from the nose or just general ill-thrift.
Significant Disease Investigation (SDI) Program
The National Significant Disease Investigation Program was introduced in 2009 to promote the full investigation of livestock disease. The program is funded by industry, state and commonwealth governments to assist with the early detection of emergency animal diseases in livestock in Australia. DAFWA has increased the subsidies available to farmers in WA to enable subsidies to be available throughout the year.
Read more about the SDI program.
Previous issues of WALDO - for producers are available on the DAFWA website on the newsletter archive page.
To provide feedback, email Dr Bruce Twentyman on firstname.lastname@example.org