Weight loss over six months, BRD confirmed

Time and location: February 2022, Queensland​​.

Case definition: Young cattle up to three years of age experiencing significant weight loss over months and ultimately dying.

Disease mapping: Three young cows from a mob of 300 doing poorly at the time of the visit. The owner had observed a similar decline in the previous two years, where a total of about 15 animals had been affected. Deaths had been in multiple paddocks (most without poison plants, although there was some lantana, yellowwood, crotalaria, poisonous peach in isolated pockets). All animals in the mob, including those that were sick, had fluid green faeces. The other animals were body condition score 3. A good vaccination schedule was being used and the mob was covered for 7-in-1, Botulism and Tick Fever vaccinations. Bovine Respiratory Disease Complex (BRD) had been diagnosed in the breeders a couple of years previously.

Gross findings: The worst affected animal had a body condition score of 1.5 (on scale 1-5), was at the back of the mob and collapsed drooling profusely when moved 300 meters. A post mortem was conducted on this heifer, and bloods and faeces were collected from the others (to rule out Johnes). Gross pathology was evident in the thoracic cavity. The lungs were very fibrosed and scarred and were collapsed to one quarter of their normal size. When cut, areas of purulent discharge was noted and this was very prominent in the cranioventral aspects. The remainder of post-mortem was unremarkable. A field diagnosis of BRD was made and a full set of samples sent for histology and microbiology.

Other differential diagnoses were poisonous plant (chronic yellow wood toxicity), BVD with persistent infection leading to mucosal disease (drooling in the worst animal), Johnes disease (considered unlikely as animals were too young to be clinical).

Laboratory findings: Histology was consistent with BRD Complex with Trueperella pyogenes, Histophilus somni, and Mycoplasma isolated from the lungs. All three animals were negative for Johne’s disease (BVD antigen ELISA and PCR on faeces).

Animal / management / environment risk factors: Recommendations to the owner focused on weaning as a potential stress period and the time when a small number of persistently infected weaners could be the source of infection.

Recommendations: Options for arranging BRD vaccination at weaning, plus dust control in the yard, not weaning in inclement weather and creep feeding so diet change is not a shock.