Rain after big dry brings disease risk

By Jeanette Severs

DISEASE RISK increases with rain events after drought or prolonged dry weather. Some of the diseases that have been affecting dairy cattle in recent weeks in Victoria’s Gippsland and Western Districts are theileriosis and acute bovine liver disease (ABLD). Parasite infections are also increasing.

Theileriosis has been known to impact up to half the milking herd, whereas some dairy farmers have found out about ABLD after experiencing losses of up to 30 per cent of their cows.

Milk fever occurs due to calcium deficiency when dairy cows are grazing green pick and standing water after significant rain increases the chance of liver fluke.

Dairy farmers are encouraged to be alert to changes in their cow behaviour and condition and know the signs and symptoms of diseases and parasite infections.

Where ABLD is clinically indicated by cow behaviour and identifying toxicity in pastures, it is accurately diagnosed by a post mortem.

Bairnsdale veterinarian Dr Jade Hammer recently diagnosed ABLD in a herd of cattle in his district, when eight cows died. He conducted post mortems on the cattle which showed extensive liver damage from the toxin. There have been several incidences of ABLD across Gippsland.

“Acute bovine liver disease is a horrible, painful death, that occurs fairly quickly after the initial symptoms,” Dr Hammer said.

“Symptoms include aggressive and agitated behaviour. Those cows that survive continue to show photosensitisation for a couple of weeks after the initial toxicity.”

While the cause of ABLD has been largely unknown, unseasonal outbreaks in Gippsland in recent years have enabled scientists and veterinarians to identify some common factors. 
It appears to be caused by fungus that forms a toxin, Drechslera spp fungi, and the seed of rough dogs-tail grass, or cynosurus echinatus, has been implicated as a host, according to Agriculture Victoria Southeast Region senior veterinary officer Dianne Phillips. Rough dogs-tail grass is also known as bristly dogstail and hedgehog dogtail.

“We’re suspicious of Drechslera’s involvement but that’s still to be confirmed with research,” Dr Phillips said.

Outbreaks have occurred a couple of weeks after good rainfall following drought or prolonged dry periods.

“We looked at climate conditions and identified an association between the outbreak and the weather,” Dr Phillips said.

Typically, the outbreak has occurred after the cows have been moved onto new pasture, typically paddocks that were restricted to cattle during the drought and showed green pick after rain.

In the Macalister Irrigation District, 20 per cent of the milking herd on one dairy farm died within the normal 12 to 24 hours of toxicity. In west Gippsland, there were losses of 10 to 30 per cent among dairy herds, with flow on effects to production in the surviving cows.

“There’s no specific treatment so farmers just have to take animals off the pasture,” Dr Phillips said.

Unfortunately, it appears improving the pasture is not a remedy to the toxin.

“It’s quite a sporadic disease,” Dr Phillips said.

Dr Hammer has seen an increase of theileriosis infections in dairy herds in his district, following autumn rain. Typically, the symptoms of pulsating jugular vein, panting, anaemia demonstrated by white gums, loss of condition and, for some cows, aborted calves, have been present. A blood test has confirmed the infection.

Hans van Wees, a dairy farmer at Tinamba, expects to see one to two diagnoses of theileria infection among his cows every year, after half the herd was infected. Diagnosis occurred after the entire herd underwent blood tests.

“It occurred after rainfall after a dry year. Half the herd was chronically infected, but fortunately only one cow died,” he said.

“We brought the cows home from an outblock, which is probably where they were bitten by ticks carrying theileria. It was just after calving and the symptoms looked just like salmonella without scours. The affected cows lost a lot of weight and that affected production.”

Veterinarians are also warning dairy farmers to be aware that rainfall after drought periods can increase the burden of parasites (leading to cases of, for example, bottle jaw), the risk of milk fever and other nutritional issues such as nitrate poisoning; all of which lead to poor health and a drop in milk production.

“Internal parasites are a problem particularly for dairy cows on dryland pastures. Rain creates a better environment for eggs to hatch,” Dr Hammer said.

Liver fluke occurs when the carrier snails become more active after a significant rain event causes standing water. Infection transfer to cattle also occurs when the snails are present around leaking troughs and on the edges of waterways and dams.

A faecal test could identify if the levels of liver fluke are low or high enough to warrant drenching.

Dr Hammer also warned milk fever and nitrate poisoning was a common problem for dairy farmers in the current seasonal conditions. Cows grazing fresh short green pasture were showing low calcium levels.

“Milk fever because of low blood calcium levels can be a risk particularly around calving time,” he said.

He recommended adding calcium to the diet through lead feeding and increasing calcium intake post calving through nutrition supplements or grazing lush green grass.

“The clinical signs of milk fever are dry nose and faeces and fast, weak pulses,” he said.

Cows with nitrate poisoning demonstrate neurological effects of staggering and shivering.

“And when you put pressure on them, for example when bringing them up to the dairy, they go down and refuse to move,” Dr Hammer said.