Suspected salt / water intoxication kills 80 cows over 3 days

Above: Cow with sunken eyes in sternal recumbency, close to comatose

Time and location: March 2025 on a cattle property in western Queensland.

Case definition: 80 Brahman-X cows transported in hot weather and then yarded with water which may have been saline, showed signs of excessive drinking, urinating, gastrointestinal pain, neurological signs, recumbency, coma and death over 1- 3 days after arrival.

Disease mapping: The cattle were loaded for transport at 6am Friday morning and arrived at the property at 3pm that day having travelled in hot weather (40-49oC). They were held in yards on water and processed on Saturday when the owner noticed one cow with sunken eyes which progressed to being staggery and recumbent. The cows were offered hay on Saturday night.

Affected animals showed clinical signs that included: excessive drinking, excessive urinating, sunken eyes, staggering, standing with back legs tucked underneath or stiff front legs, green watery diarrhoea, swollen anus, sweating, diving into the dam and aggression. Some cows aborted. The cows had previously been vaccinated for botulism and 7 in 1.

Cows died in the yards and paddock; deaths were not clustered. Symptoms appeared within 24 hours of arrival at the property and progressed over 3 days. Some animals that were sick slowly recovered.

No deaths had occurred in 500 steers that were in these yards one week beforehand. There were no deaths in a mob of 130 cows that were trucked and handled the same way and went to another set of yards 100km down the road.

Gross findings: Two moribund cows were autopsied. Both had excessive fluid in the rumen and rounded livers which spilled blood on cutting and dark purple discolouration of some tissues (mesenteric lymph nodes, lung).

Differential diagnoses considered:

• Water deprivation/salt toxicity
• Transit tetany
• Toxins (?) added to water
• Lead poisoning
• Thiamine deficiency induced polioencephalomalacia (PEM)

Laboratory findings: Histology showed nephrosis in both animals, with acute tubular necrosis and haemoglobinuria in one. In conjunction with the history and clinical signs, this supported the diagnosis of salt toxicity causing the high mortality rate.

Unfortunately delays in the transport of samples due to Topical Cyclone Alfred meant that unpreserved tissues and bloods and aqueous fluids were unsuitable for analysis.

Management / Environment / Animal risk factors: A combination of predisposing factors increased the risk of acute water deprivation / salt toxicity: the cows being withheld from water; travelling in trucks in the middle of the day during extreme heat; un-adapted cattle being introduced to water with higher salinity than they were accustomed to; the trough in the yards not being cleaned and emptied prior to use by this mob (salt built up): allowing animals to rehydrate too quickly.

Deaths following water deprivation occur when the animals rehydrate and cerebral oedema develops due to sodium imbalance and sudden movement of water into the brain. Acute renal insult and intravascular haemolysis can also occur.

Recommendations to prevent future cases:

• Ensure cattle are transported during cool weather or at the coolest time of the day and not off water for extended periods.
• Check water supplies regularly, to ensure cattle are not withheld from water.
• Don’t allow thirsty cattle to gorge themselves on water, only allow access to small amounts of water frequently until rehydrated. Aim to rehydrate over 24 hours.
• Consider water quality testing.
• Use a different set of yards with improved water quality for introduced cattle to avoid sudden exposure to saline water.
• Consider carting fresh water if required to transport to affected yards.
• Regularly clean the troughs