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Deaths at mustering – possible metabolic

Unusual presentation: 

The station had repeated events of cows in good body condition going down during mustering and dying.

Time and location: On the Barkly Tableland, April 2018.

Case definition:Cows in body score of 3.5 or above going down at mustering, with signs of hind limb paresis, increased aggression, distress, paddling and death within 1-2 hours.

Gross post mortem findings: A cow with mild ataxia at mustering went down in the yards during a preg test visit and was subsequently euthanased for autopsy. She was approximately 17 weeks in-calf, in good body condition and had a normal body temperature (38.2oC). No gross abnormalities were observed and the rumen was full.

Laboratory findings:  No pathology was evident in the tissues that were submitted: liver, spleen, kidney, brain, spinal cord, rumen and small intestine. Although there was no definitive finding, pregnancy toxaemia and ketosis was unlikely for this cow (there were no hepatocellular changes and beta-hydroxybutyrate levels were normal) and heamoparasites were not detected.

Some blood parameters were outside the normal range, in particular the potassium level was high and phosphorous was low. The lab regarded the low serum phosphorous level as a significant finding and worthy of further investigation.

Animal / management / environment risk factors: Paddocks were already in drought condition early into the season, with poor energy/protein content of feed.

Recommendations to the producer:At autopsy the working hypothesis for the mortalities was ketosis. The station was advised to keep Calcigol on hand and to monitor the response to treatment of affected cows. The potential for phosphorous deficiency, as suggested by the lab testing, was also seen as feasible given the poor feed. The vet discussed options for assessing phosphorous levels in the herd but unfortunately further work-up was rejected by the manager. It was later learnt via a contract musterer that the mortalities had continued.

Histo revealed the heart muscle pathology in this SDI (slide from Berrimah Vet Lab)
Above: The lab regarded the low serum phosphorous level as worthy of further investigation.