This report describes an outbreak of septicaemia and respiratory disease in a feeder enterprise.
When a well run 200 cow milking herd ceased dairying four years previously, the owner converted the operation to a weaner fattening enterprise. 2,000 to 2,500 calves are introduced per year, with the majority purchased through saleyards. Typically they are introduced at 120 - 160kg liveweight, are on grain an average of 75 days and sold at 220kg through the yard. Calves are bought on price and weight and not on quality or gender, with the view to value adding. The ration is barley, hay and silage based, mixed on site with the support of a nutritionist for formulation. Much of the feed is grown on farm. Management is good, growth rates are typically 1.1- 1.3kg/day and the calves turned off in excellent condition. They are 5 in 1 vaccinated, but not Mannnheimia or Pestivirus vaccinated. Background morbidity and mortality rates are low. Only about 15 calves have died in the past 4 years. The calves are checked twice daily and any that appear off feed are pulled from the lot, examined by the owner, temperatures taken and treated with antibiotic if over 40oC or have signs of respiratory distress. Oxytetracycline, Cetftiofur and Tilmicosin have been used.
In the week prior to the first property visit, three calves presented with fever (>41oC), marked respiratory distress, an oral white stable frothy discharge and malaena. They were from different weight groups. One had responded to treatment with antibiotic. One had just died and the other was near death at the time of property visit.
On examination the sick calf had freshly clotted blood casts in the faeces, was in severe respiratory distress, had a deep hacking cough, normal temperature, but unwilling to move. It was shot for autopsy.
The recovered calf had been found in early stages three days previously; it was febrile, was coughing and had malaena. It was treated with Oxytetracycline daily for three days. After two days its faeces and temperature returned to normal. On examination it had a normal temperature, marked dyspnoea and cough.
The calf that died had evidence of dark malaena. The animal was dehydrated. Throughout the carcase there was evidence of petechial haemorrhages, including muscle planes, serosal surfaces and omentum. There was extensive fluid in thorax, which quickly clotted on exposure to air. The thoracic cavity had large amount thick fibrin adhering to lungs and this was also in the pericardial sac. The lungs were deflated and small. The airways were filled with a 'beaten egg white' froth. The gastrointestinal tract distal from and including abomasum was filled with clotted blood. The sources of the haemorrhage were a series of small abomasal ulcers and diffuse haemorrhage from the pyloric mucosa. There were healed ulcers which were larger than those that haemorrhaged. All lymph nodes and the spleen were enlarged.
The euthanased calf had mild to marked petechial haemorrhages throughout the carcase. There was excess yellow thoracic and pericardial fluid which clotted quickly on exposure to air. The lungs had gelatinous fluid between the lobes and were oedematous. All lymph nodes and the spleen were enlarged. There were frank blood clots in LI and caecum only. The source of the haemorrhage appeared to be from several small ulcers in distal ileum, just proximal to the ileocaecal valve.
The dead calf had moderate diffuse periacinar fatty change in the liver with occasional hepatocellular necrosis. The lung had prominent diffuse oedema, with light pink proteinaceous fluid in airways. There was severe diffuse subpleural oedema with dilated lymphatics. The heart had no significant histopathologic abnormalities. The Bowman's spaces in the kidneys were diffusely distended with proteinaceous fluid.
The euthanased calf had areas of emphysema, greatly distended interlobular septa by oedema and dilated lymphatics in the lungs. The liver had mild diffuse periacinar fatty change. The heart had focal subpericardial haemorrhage, but no significant changes. There were no significant changes in small intestine. Moderate to severe acute multifocal to segmental mucosal and submucosal haemorrhages were observed in the large intestine.
Comments: Severe pulmonary oedema in both animals. Mild to moderate anoxia/ketosis in both. Moderate to severe intestinal haemorrhages in the euthanased calf.
Cultures of lungs were overgrown with contaminants.
A week later the owner rang with two further autopsies, one in the morning from a calf that had been sick with fever and respiratory distress, but no malaena, for two days and treated. The other was later in the day from an older calf that was found dead without any signs, despite the mob being inspected twice daily.
The first calf had diffuse petechial haemorrhages on all serosal surfaces. It had increased thoracic and pericardial fluid which clotted on exposure to air. The ventral lung lobes were consolidated from what was suspected to be a past respiratory infection. There were areas of recent haemorrhage in the dorsal lobes and interlobular gelatinous oedema. There was stable white frothy discharge in the airways. Because it had been treated with antibiotic no swabs were taken.
The second calf had yellowish discharge from nostrils. The oral mucosa, conjunctiva and entire carcase were markedly jaundiced. It had early onset rigor. There were marked extensive petechial haemorrhages throughout carcase including serosal surfaces, muscle planes, epicardium and endocardium. All lymph nodes throughout carcase were very enlarged. The spleen was grossly enlarged with rounded edges. The urine was port wine in colour. The kidney cortices were dark. The liver was swollen, friable and coppery coloured. The lungs had patches of haemorrhage. There was stable froth in the airways. There was much less thoracic fluid than in the others, and it was slow to clot on exposure to air. Because the autopsy picture closely resembled Tick Fever samples to exclude Babesia were taken. No ticks were found.
Histophilus somni was cultured from the lung swab of the second calf. Tail hair from this calf was also PACE positive for Pestivirus. Samples for Tick Fever were negative.
Based on the presentation of the initial cases, a presumptive diagnosis of Histophilus was made. Confirmation required a week's wait until an untreated calf was available for culture.
The findings in this case study were consistent with the Histophilus somni disease complex as described by Parkinson et al. (2010). Pestivirus persistent infection would have predisposed the second calf to the infection. The case was referred to the owner's private veterinarian for treatment and consideration given to in feed medication. Despite the attention to detail to detect and treat cases early, the course of the disease was too quick to enable effective treatment in most cases.
A decision was made to in feed medicate with Oxytetracycline at the rate of 2kg / tonne.
A press release for an increased Export Slaughter Interval for OTC to 90 days came two days after commencing medicated feed.