This case involved the loss of 151 Brahman steers ex 2250 introduced to an extensive beef grazing property in the Buccarumbi district near Grafton, NSW. The cattle were purchased in the Northern Territory, assembled for transport and moved to a company owned cattle station at Buccarumbi.
The area is renowned for rainforest gullies with creek flats pastures of paspalum, kikuyu and native carpet grass. There is an abundance of thick, dense red flowered lantana up the hillsides along with other poisonous plants such as Poison peach, mother of millions, bracken fern, rock and tree ferns, and wild passionfruit.
The stock arrived hungry and during a fairly wet autumn the first losses were noticed about a week after introduction. Losses continued for approximately three weeks with many affected animals subsequently recovering while others died. The mortality rate overall was 6.7% but may have been higher as after the initial diagnosis the owner did not report the final number. The morbidity rate was about 15% so that it was estimated that about 300 steers were showing variable clinical signs during the course of the outbreak. The survival rate among affected animals was about 50%.
The initial signs in an affected animal are a loss of appetite with depression and standing aside from the mob in the shade. There is frequent urination followed by constipation and dehydration. Jaundice is a sign that appears in 1-2 days with photosensitisation of non-pigmented skin, especially the muzzle.
Death usually takes about 2 days in severely poisoned cattle with less severe cases taking 1-3 weeks to die. Affected animals do recover sometimes.
Weight loss and subsequent poor productivity are important signs as well as a recovered mob may remain suboptimal performers for 12 months after the event.
The main finding is jaundice. Early rapid death cases may not exhibit photosensitisation. The liver is swollen and ochre-coloured with the gall bladder extremely distended with green-coloured watery bile. Kidneys may also be swollen and pale. The bladder is often full and the rectum may be packed with firm leaved faeces. I often also find a firm packed omasum as well due to ruminal stasis. Weight loss including emaciation has been noted in more chronic long standing cases.
In this case gross pathology was sufficient to give a rapid field diagnosis but samples of fixed and fresh liver and kidney were submitted. Difficult cases can be assisted by histopathology of these organs from a post mortem. Alternatively serum liver enzymology usually shows significant elevations in advanced clinical cases.
Consistent histopathological findings include swollen and degenerative hepatocytes, distension of the bile ducts with some bile plugs and renal tubular degeneration with the finding of hyaline/proteinaceous casts.
It is rare to require laboratory diagnosis as clinical signs are typical given the history and presence of the plant on the affected property.
Rapid treatment with a drench of 2.5kgs of activated charcoal can be efficacious if given early in the course of the poisoning. Electrolytes should also be given to alleviate the dehydration. Activated charcoal can be hard to get hold of so I have noticed it is available at aquarium shops where it is sold as a water filtering agent. Ordinary charcoal is not effective.
I also recommend antibiotics and anti-inflammatory drugs be given as well. Sodium bentonite is a poor alternative to activated charcoal but may be used when activated charcoal cannot be obtained.
Successful treatment rates vary depending on how long ago poisoning occurred and the dose of toxic principle consumed. Keeping animals in the shade, providing plenty of cool clean drinking water and covering photosensitised skin with sunscreen have all been tried with variable success.
This is where opinions tend to differ somewhat. Options that are consistent with most observers include
Other things that are done but not proven to work include
Lantana poisoning is the single most prevalent cause of stock losses in the Grafton RLPB. It is estimated that approximately 5000 head of cattle are poisoned each year. Some years are worse than others and some herds experience constant problems while others do not. Individual cattle have variable tolerance with some cattle noted perfectly well despite living on a diet of lantana while other individuals are poisoned by a few flowering tops.
There is still much work to be done to reduce the incidence of outbreaks and a persistent education campaign is waged concentrating on new owners contemplating introducing stock from non-endemic areas.