Severe milk drop in dairy cows, 13 of 700 head affected, 3 dying within 24 hours of showing signs.
Above: Two cows post-mortemed had extensive haemorrhages across all serosal surfaces.
Time and location: Far North Queensland, May 2020.
Case definition: Adult cows present with lethargy, abdominal respiratory effort, low rumen fill and aimless wandering. Signs progress to abdominal kicking, hypersalivation and lateral recumbency in severely affected cases. Pale mucous membranes, small blood clots in the rectum and tachycardia may be evident at clinical examination. Some cases die.
Disease mapping: 13 cases in herd of 700 Jersey and Holstein Friesian milking cows.
Gross findings: Post mortem of 2 cows showed petechial and ecchymotic haemorrhages across all serosal surfaces, diffuse mottling of the cut surface of the liver, distension of the small intestine (especially ileum) with thick, frank blood coating the mucosal surface (no large clots).
Differential diagnoses were: Jejunal Haemorrhagic Syndrome (JHS), salmonellosis and acute hepatic toxicity – possibly Acute Bovine Liver Disease. Bracken fern and Lantana poisoning occur in the area but did not fit the case description.
Laboratory findings: Full samples submitted for post mortem cows, and blood and faeces from a clinically affected case that survived. All three had elevated liver enzymes, especially GLDH. There was severe, acute haemorrhagic necrosis of both livers with histopathology (cell types and thrombosis patterns) suggestive of a toxaemic/septicaemic process. Clostridium perfringens was isolated from both small intestines. Intestines, lymph nodes and faeces were salmonella negative. No coccidia or cestode eggs in the faeces and a low level of strongyle eggs. The diagnosis was suspect JHS.
Animal / management / environment risk factors: Feed for the herd was pasture-based with no access to silage or changes in the grain ration fed during milking. The autumn pastures had been heavily grazed and it was noted that weeds and lower branches of rainforest flora had been eaten in paddocks bordering the rainforest.
Recommendations to the producer: This disease event was characterised by liver damage and haemorrhage. Although no further cases have occurred since the submission, the producer is concerned about ongoing production losses in subclinically affected cows and the potential for future outbreaks. In the absence of a definitive diagnosis the following recommendations were made:
- Reduce herd size to decrease grazing pressure and minimise the feed gap heading into winter months.
- Vaccinate adult cattle with 5 in 1. Although it is not believed to be the primary cause of death, Cl novyi and Cl perfringens were both isolated on post mortem, and likely contributed to disease pathology.
Above: Organs had petechial and ecchymotic haemorrhages, cut surface of liver had a diffusely mottled appearance.
Above: Distension of small intestine, with thick, frank blood coating the ileal mucosa (but no large obstructing clots).
Above: Grazing rotation in recent weeks had included paddocks bordering dense rainforests.