Pregnancy toxaemia in transported cows

Left and central: On post mortem the livers of both cows were swollen, yellow and friable.
Right: Urinalysis on dipstick strongly positive for ketones.

Time and location: June 2024, Western Australia.​

Case definition: Late pregnant cows transported approximately 300km showing neurological signs, recumbency and death within 3 days.

Disease mapping: 860 cattle from one property in Western Australia were trucked about 300km to export yards with deaths occurring on the truck (2) and within 3 days of arrival (5). Cows showed signs of staggering, muscle tremors, hind limb knuckling, inability to rise and aggressive behaviour. 12 cows from the same mob had died during transport to the Northern Territory the week before. Approximately 8 cows which were affected were reported to recover without treatment. One aborted foetus of about 5 months gestation was observed in the yards. A veterinary investigation was requested on day 3. Two severely affected cows had bloods collected and were euthanised by captive bolt for post mortem examination.

Gross findings: The cows were heavily pregnant (approx. 8 months in calf). The liver in both appeared mildly yellow in colour and was a friable cheesy consistency. A urine sample collected from the bladder indicated ketone levels of 3+ on urine dipstick test. No other significant abnormalities were detected.

Field differential diagnosis: Pregnancy toxaemia was considered the most likely diagnosis. Other differentials included hypomagnesaemia, other mineral deficiency (hypophosphataemia, copper, vitamin A, cobalt, B12), plant toxicity (pyrrolizidine alkaloid) and botulism.

Laboratory findings: Histopathology showed marked hepatic lipidosis in both cattle. Clinical biochemistry showed: elevated ketone bodies (Beta-hydroxybutyrate); mildly elevated liver enzymes and elevated plasma vitamin B12; elevated muscle enzymes (likely due to transport); adequate selenium (as GSHPx) and plasma copper.

Animal / management / environment risk factors: Pregnancy toxaemia usually occurs in cattle during the last 2 months of pregnancy when cattle don’t have sufficient quantity or quality feed in the rumen. The liver is unable to make enough glucose to utilize incoming fat which is mobilized during late pregnancy as an energy source (as feed itself is not enough to maintain the cow and the calf). Negative energy balance causes ketones build up in the blood affecting the nervous system of the animal. Being yarded up and trucked had restricted feed for these cattle which likely precipitated this disease event.

Recommendations:

• Immediately – keep these cattle on feed for the next 5-7 days, pregnancy test the mob and remove the heavy pregnant cattle. Pregnancy test cattle on the station before sending them to the export yards.
• In the future – have cattle in a positive energy balance leading into calving by ensuring pasture feed is adequate or supplementary feeding. Do not transport cattle when they are heavily pregnant (over 7 months in calf) as this places excessive stress on their bodies which can deplete their energy stores and lead to pregnancy toxaemia. Pregnancy testing should be performed prior to sale.