Solanum is a large genus of flowering plants and contains a number of important staple foods, including the potato and the tomato , and a range of poisonous plants. Plants in this genus produce many toxic alkaloids, including solanine, in their leaves, fruit, and tubers . A number of mammalian species are known to be at risk to toxicity, including cattle, sheep, goats, chickens, ducks, horses, rabbits, dogs, and humans. Swine are believed to be especially susceptible . This report details a case of suspected sticky nightshade (Solanum sisymbriifolium) toxicity in a Greater Sydney beef herd.
During December 2014 an 8-10 month-old steer developed hind limb ataxia on Day One. The animal went down on Day Two, though continued to try to rise throughout the day. The animal was in lateral recumbency by the morning of Day Four. It had been bought three months previous in very poor condition. The animal had been vaccinated with a single dose of a 5-1 vaccine (trade name not specified) and drenched with ivermectin (1 ml/10 kg topically; Paramax, Cooper's Animal Health) on arrival. The animal was one of a group of twenty that had access to approximately five acres of pasture broken up into three paddocks. There had been no recent changes in paddock access (the animals were grazing on all three paddocks). The animals were receiving a considerable amount of grain, however there had been no recent changes in feeding practices.
During the end of January 2014 the owner lost ten out of approximately twenty animals after the herd was given access to a previously-ungrazed paddock on the property. No clinical signs were noted in the history. A toxic plant was suspected to have caused the deaths but no definitive diagnosis was made. An additional two animals were lost at the beginning of February 2014. A private practitioner attributed these later losses to grain overload. The owner had been grazing cattle on the property for more than forty years and, prior to January 2014, had no major animal health issues.
The affected animal was in lateral recumbency and moribund. Mild trauma attributed to struggling to rise was observed on physical exam, otherwise there were no abnormalities noted. The animal was euthanized with a captive bolt gun and a post-mortem was conducted.
Post-mortem examination revealed no significant findings. Blood and fresh and fixed liver and kidney samples were collected for laboratory diagnostics.
Biochemistry revealed an AST of approximately 3.5 times normal, a markedly elevated CK, and mild azotemia, and haematology revealed a mild neutrophilia, all of which are consistent with prolonged recumbency. Blood lead and nitrate/nitrate levels were within the normal limits.
Histology of the liver sample revealed mild hepatocyte necrosis while histology of the kidney sample revealed renal tubular dilation. These changes were interpreted by the pathologist as being unlikely contributors to the steer's death.
On Day Seven a second steer of a similar age developed hypersalivation and ataxia. It also appeared disoriented. At that time the paddocks were thoroughly examined and the presence of large amounts of sticky nightshade was noted. The plant had also obviously been grazed on by the animals. The recommendation was made to remove the remaining animals from the paddocks and confine them to the available pens. The second affected steer died the following day.
On Day Ten a third animal became acutely ataxia, blind, and died within four hours. This last mortality occurred the day after the animals were removed from the paddocks. There were no further mortalities.
Toxic doses of solanine can cause significant mortality events in livestock species. Solanine toxicity often presents similarly to atropine toxicity as both can cause pupillary dilation, ataxia, muscular weakness, restless, thrashing, and changes in mentation [3,4]. In addition, diarrhoea, hematochezia, anorexia, and hypersalivation can occur with solanine toxicity - these signs are due to the fact that solanine is a gastrointestinal irritant, unlike atropine . Dyspnea and signs associated with hemolysis have also been reported. The duration of clinical signs can range between a few hours and 3-4 days . When ingestion is acute the majority of affected animals die, while in less acute cases animals may present with mild jaundice, weakness, incoordination, muscle tremors, tachypnea and bloat but may recovery [3,4]. The time from ingestion to onset of clinical signs can vary anywhere between a few hours up to twenty-four hours [3,4], which may explain the death that occurred after the herd was removed from the paddocks.
Post-mortem findings are highly variable, and it is not uncommon to find no gross lesions in cases involving sudden death. The kidneys may be pale and surrounded by clots and edema, and histological findings can include tubular necrosis. Lesions of the gastrointestinal tract can be minimal, or may include marked hyperemia, hemorrhage, and ulceration. Other non-specific findings include liver congestion, gallbladder distension, edema of the ventral body wall, congestion and emphysema of the lungs, and splenic and cardiac hemorrhage and congestion .
Toxicity often presents when pasture is overgrazed, however in this case the sheer abundance of sticky nightshade is suspected as the cause (see images). Within the Solanum genus is it generally the leaves and green fruits that are most toxic and many cases of poisoning have been reported due to ingestion of green fruits [3,4]. In this case individual plants were heavy with green fruits and their ingestion may have been the cause of the mortalities in this case. Further, solanine content increases up to maturity , which may explain the seasonality of the mortality events on this property.
There is no specific therapy for affected animals. In cases involving high-value animals where acute ingestion is known to have occurred, decontamination and activated charcoal and fluid therapy may be pursued. Pastures should be mowed before the fruits ripen to prevent plants from propagating. Herbicides may also be used [3,4]. Currently there are no registered chemical options for this particular Solanum species, but a herbicide containing triclopyr, picloram, and aminopyralid (GrazonTM Extra, Dow AgroSciences) is registered for similar weeds. Both pasture management techniques have been recommended to reduce the quantity of sticky nightshade and prevent future mortalities on this property.