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Heifers collapse in hindlegs with necrotic myositis

Unusual presentation:

Five young heifers from a mob of 300 Brahman with hindleg collapse.

haemorrhage behind tibia and ruptured gastrocnemius muscle
Above: Haemorrhage behind the tibia and ruptured gastrocnemius muscle​.

Time and location: March 2023, Queensland.

Case definition: Young, newly-weaned heifers unable to walk on hindlegs, using only the front legs to move. Otherwise bright, alert and able to urinate and defecate normally.

Disease mapping: Problem first seen two days after the mob of mixed sex 4–7-month-old Brahman calves were weaned. The mob came from a flood plain that backed onto basalt ridge country. They were yarded and moved by road transport to a new property. The yarding included some of last year’s mickey bulls. Cases were only observed in the heifers.

Gross findings: The viscera of an affected heifer that was post mortemed were all grossly normal. There was a large amount of haemorrhage and bruising posterior to the tibia and a full width, mid-body tear in the gastrocnemius muscles of both hindlegs. Skeletal muscle, kidney, heart and liver were submitted to the laboratory. Clotted blood was collected at random from 10 animals from the weaner mob: 5 males and 5 females.

Laboratory findings: There was moderate to marked necrosis and degeneration in the skeletal tissue of the gastrocnemius muscles, with haemorrhage extending into adjacent fascia in some areas. The liver showed generalised hepatic lipidosis. There was moderate to marked subacute interstitial nephritis and renal tubular injury. No significant findings in the heart. Creatinine kinase levels were high in 8 of the 10 serum samples. Selenium serum levels were at the low end of the normal range for all five heifers, and the low end of the normal range in the post mortem liver sample.

Animal / management / environment risk factors: It is possible that that riding of the heifers by the mickey bulls led to the gastrocnemius muscle rupture. While selenium deficiency was not recognised in soils on the property of origin, significant rain events in the first quarter of 2023 did move soils at the root zone of pastures. All heifers were treated with 5 mL Cobalife B12 plus Selenium, and Selovin LA.

Recommendations: No further injuries occurred. It was recommended that lick blocks with Selenium be provided in the breeding paddocks on the floodplain and to make sure all bull calves are castrated each year.