Unusual presentation: 50 weaners dead over 8 days with cases ongoing.
Time and location: Barkly Tablelands, July 2019.
Case definition: Daily on-going deaths in early weaned cattle, with 4-7 deaths each 24 hour period for the last 8 days (in a mob of about 800 weaners). No definitive clinical signs – some animals coughing, some have an obvious nasal/ocular discharge. Animals were weaned early due to the rapidly deteriorating condition of the cows and many are poorly developed. They are now on feed in the main station yard.
Gross post mortem findings: The Manager did an initial post mortem of 2 cases. The photos taken showed one animal with obvious lung pathology and another with minimal to no respiratory involvement. The subsequent veterinary investigation included a detailed history (from station staff), examination of the feed yards and post mortem of 3 cases:
- Weaner 1 – depressed, febrile with moderate scouring. Euthanised. Had moderate lung pathology with consolidated ventral lobes containing purulent nodules, fibrinous adhesions.
- Weaner 2 – had been dead for about 6 hours. Had significant lung pathology, grossly enlarged gall bladder plus enlarged liver.
- Weaner 3 – depressed, febrile with mild oculanasal discharge and severe dehydration. Euthanised. No gross pathology evident.
A full set of fresh and fixed tissues and bloods were submitted to the lab.
Laboratory findings: There was a range of pathology so we’ll cut to the laboratory diagnoses:
- Weaner 1 – mild erosive suppurative enteritis (combination of intestinal coccidiosis and probable enteric colibacillosis) and a subacute moderate suppurative bronchopneumonia
- Weaner 2 – moderate acute haemorrhagic bronchopneumonia (with culture of E coli and Strep bovis from the lung swab), and a suppurative liver infection (likely due to bacteria ascending from the intestine)
- Weaner 3 – no major pathology, a mild regional pulmonary oedema and intestinal coccidiosis.
The findings are not suggestive of a major outbreak of bovine respiratory disease (different types of lung pathologies and culture of opportunistic pathogens). The range of findings probably relate to the stress of early weaning and immunosuppression.
Animal / management / environment risk factors: The weaners were noted as being poorly developed and probably immunosuppressed at the time of the property visit due to the extremely poor seasonal conditions. The station staff were seen as doing a good job of actively managing the breeder herd and subsequent weaner health issues.
Recommendations to the producer: The recommendations aimed at making practical improvements in the difficult circumstances.
- Pen animals according to size and reduce pen density
- The animals were immature/poorly developed. Some 6-week old calves; most were older but under-developed (~80-100kg animals). No real segregation of animals had occurred.
- Recommendation: Split the six feed pens into more even lines based on weight and apparent age. To reduce animal density, move the healthier 50% into adjacent holding paddocks if suitable feeding/water facilities can be improvised.
- Eliminate close contact with adult cattle
- The weaners were in pens between feedlot pens of older cows/bulls, increasing the chance of direct transfer of pathogens.
- Recommendation: Ensure at least an empty pen or laneway between adult cattle and these animals.
- Pick out sick animals earlier, treat and isolate
- The increase in mortality and morbidity correlated to a significant cool windy change in the weather, as well as arrival and subsequent removal of 2200 healthier weaners from the yards.
- Recommendation: You can’t change the weather, but do increase diligence of monitoring and treatment during this type of risk period. Continue actively treating with antibiotics. Identify sick animals earlier for improved response to treatment and isolate from others to reduce transmission
- Don’t vaccinate these animals at this time
- Respiratory signs (coughing, discharges, depression) were present but not to the extent expected in a significant BRD-type outbreak.
- Recommendations: BRD vaccination will have little beneficial response in animals are that immune-suppressed.
- Treat scouring weaners for coccidiosis
- A moderate amount of scouring was present but no gross bloody diarrhoea.
- Recommendation: Earlier identification and treatment for coccidiosis (confirmed by the lab).
- Improve the diet
- The weaners were being fed hay and generic weaner pellets which is not an adequate diet.
- Recommendation: Younger animals need calf crumble/calf feed which includes milk replacer and feeding more frequently (as per company’s early weaning ration). Consider chopping the hay to allow better utilisation. Supply molasses to all pens to increase energy levels.