Datura ferox is an annual forb of the Solanaceae family known by the common name fierce thornapple (also 'long-spined thornapple', 'long-spurred thornapple', or 'false castor oil plant') (Cunningham et al., 2011). There are six species of Datura naturalised in Australia; all are potentially poisonous, containing a range of tropane alkaloids including scopolamine, hyoscyamine, and atropine (McKenzie, 2012). Few reports exist of Datura spp. toxicity in cattle, and, since the plants are considered unpalatable and rarely grazed, contaminated feed is thought to be the most common source. This can occur when plants are incorporated into hay or silage, or when seeds contaminate grain used for livestock feed (McKenzie, 2012). This report describes a case in which cattle grazed mature Datura ferox plants and subsequently presented with clinical signs consistent with tropane alkaloid toxicity.
In late February 2016, a mob of around 120 steers (approximately 16 months old) was walked from a mixed pasture paddock to a holding paddock close to cattle yards, in preparation for weighing the following day. No illness was observed at this time. The following day, as they were moved from the holding paddocks to the cattle yards, one animal was observed with an abnormal gait and jaw champing. When the mob was checked the following morning, nine animals were separated from the mob, had an altered gait, apparent blindness, and hypersalivation. Mild diarrhoea (with some mucus) was also noted in some animals. The following morning thirteen animals were affected - some were animals which had been affected when signs were first observed, others were animals which had not been affected the previous day. Affected animals were yarded for examination later that morning.
Eleven animals judged by the manager to be affected were separated from the mob for closer examination. When observed in the yards, most appeared agitated (the manager considered them to be usually quiet cattle). Some had a mildly stiff gait, with mild hypermetria of the forelimbs. One was jaw champing and compulsively chewing fence rails and other objects. Given the history of multiple animals presenting with lameness, hypersalivation, and jaw champing, excluding exotic vesicular diseases was considered a priority. A thorough oral examination was performed on all eleven animals - no vesicular or ulcerative lesions were observed. No obvious vesicular lesions were observed on the feet.
Other clinical signs and numbers affected are summarised below:
Muscle fasciculations: 5/11
Decreased or absent menace response: 5/11
In all animals with a decreased or absent menace response, the pupillary light reflex (direct) was present. Pupils did not appear markedly dilated.
Blood samples (EDTA and serum tubes) were collected from affected animals.
The paddock in which the mob was originally grazing consisted of mixed grass species (predominantly liver seed grass, Urochloa panicoides), and overall feed availability was good. The paddock contained two bore-fed water troughs, located at opposite ends of the paddock. On inspection, the trough where the mob usually camped was dry - the manager was unsure how recently this had occurred. The second trough was full and the water appeared clean, with no obvious gross contamination or odour.
Surrounding the full trough was a large area of Datura ferox. Both leaves and fruit had been extensively eaten. The manager reported that prior to being moved to the yards, the mob had been camped around this water source.
No sources of lead or other chemicals were found in any of the paddocks recently grazed by the mob.
The affected mob was moved to a mature lucerne paddock. No specific treatment was given. Within 2 days all affected cattle had recovered.
EDTA blood samples from 11 clinically affected animals had lead levels <0.10µmol/L.
Datura spp. contain a range of tropane alkaloids (including scopolamine, hyoscyamine, and atropine) that affect the nervous system of all animals species (McKenzie, 2012). All parts of the plant are toxic, and toxin levels have been shown to vary significantly - one study reported a range of alkaloid levels from 0.012% to 0.47% by weight (McKenzie, 2012). These toxins have a sympathomimetic action, and the following clinical signs have been reported in cattle (Radostits et al., 2007; McKenzie, 2012):
In this case, many of these clinical signs were observed. Marked pupil dilation was not present, but a decreased or absent menace response was recorded in 5/11 animals. The differential diagnoses in this case were:
Lead toxicity was excluded by laboratory testing. Thiamine deficiency and sulfur-induced PEM were considered less likely based on history and clinical presentation. Given that one trough had emptied, salt toxicity/water deprivation was considered possible. However, the manager reported that the stock had been found camped near the second (full) trough prior to being moved and none appeared dehydrated. Foot and Mouth Disease was excluded clinically.
Surrounding the full water trough was an area of Datura ferox which appeared to have been extensively eaten. This fact, combined with clinical signs consistent with tropane alkaloid toxicity, was considered sufficient for a presumptive diagnosis.
Datura spp. are “usually unattractive to animals and are rarely eaten”, with most cases of poisoning occurring when plants are incorporated into hay or silage, or when seeds contaminate grain used for livestock feed (McKenzie, 2012). In this case, however, mature plants were extensively eaten. It is possible that cattle ate the unfamiliar plants after being forced to move from their usual water source.
Because tropane alkaloid toxicity causes ruminal atony and appetite depression, cases may be self-limiting and therefore rarely fatal (Nelson et al., 1982; Radostits et al., 2007; McKenzie, 2012). In this case all animals recovered within 4 days, following removal from the paddock containing Datura ferox plants.
Thanks to the manager for providing a detailed history and the two Datura ferox photos.