Salmonella orion and cryptosporidia were cultured from faeces following the death of approximately fifty calves in a herd of 150 Angus cows with calves at foot run under extensive conditions near Goodooga, NSW. The property lies within the Darling Livestock Health and Pest Authority. Private practitioner Martyn Powell (Western Namoi Veterinary Services) investigated the cause of calf deaths after telephone consultation with veterinarians from the North West LHPA.
Initially approximately twenty calves from a mob of 150 Angus cows with calves at foot were found dead by the owner. The herd had been checked fourteen days previously. It had then rained for three to four days and it was estimated that deaths had been occurring since the rain ceased. All dead calves were less than eight weeks of age, with the majority being two to four weeks of age.
At the time of examination, there were four clinically ill calves. They exhibited fever, depression, dehydration and profuse white diarrhoea. Thirty subsequently affected calves died despite multiple treatments with antibiotics (oxytetracycline and trimethoprim/sulphur) and electrolytes. Four of the calves also received NSAID medication. Deaths occurred within a few days of onset of diarrhoea. In total, the deaths occurred over a three week period.
A necropsy was conducted on one dead calf with gross changes including inflamed intestines and signs of agonal death. Histology was unrewarding due to autolysis. Faecal samples were taken from two affected calves with one sample having a positive culture for cryptosporidia, and both samples culturing Salmonella. A faecal sample taken from the large intestine of the autopsied calf was also positive for Salmonella. Salmonella orion was typed from all three samples.
Although Salmonella orion is largely unknown as a pathogenic species in cattle, the clinical course of the syndrome seen in these calves support its aetiological involvement. It would be unusual for cryptosporidia alone to present as such an extreme cause of deaths in extensive circumstances in this region. S. orion has been isolated from the intestines of cattle as slaughter in abattoirs in Australia. It is speculated that a decomposing calf found in a water trough at the time of examination may have been the source of S.orion for other calves.