Nicotiana glauca (tree tobacco) is an upright, small, spindly tree with broad, elliptical, bluish-green leaves and pale yellow, tubular flowers6 (Fig 1 & 2). It is an introduced species of Argentina and regarded as an environmental weed in Victoria, South Australia, Western Australia, Northern Territory, Queensland and New South Wales10.
N. glauca grows in a wide variety of habitats. It is well distributed throughout the region of western New South Wales and is considered a problem in drier, inland regions in the southern parts of the country2 (Fig 3). Interestingly, N. glauca is most prevalent in areas in which the soil has been disturbed in some manner2.
N. glauca belongs to the plant family Solanaceae and contains pyridine alkaloid toxins6. The main alkaloids in this plant are anabasine and nicotine. Ingestion of N. glauca can cause death or they may act as teratogens7. Cattle, sheep, goats, pigs, ostriches, rabbits and humans are recorded as having been affected by this plant4,6.
In January 2013, a property in the far Western Division of NSW was visited by a NSW DPI Veterinary officer after a producer reported death and illness in cattle. The producer had a group of four Angus yearling heifers, three of which were found dead either in or near a creek on the Darling River. The three heifers had been dead for many days so necropsies were not performed. The fourth animal was recumbent, and made several unsuccessful attempts to rise. The ground around her indicated she had been struggling to rise for some time. She was alert and responsive with normal temperature and respiration. Other than her inability to rise and mild dehydration, there were no abnormal clinical signs. Daytime temperatures were in the high thirties and there was a lack of green feed except for clusters of what was subsequently considered to be N. glauca, growing amongst the river stones in the creek.
Blood samples were collected from the surviving heifer and sent for analysis. The biochemistry and haematology results were unremarkable showing only mild changes in association with dehydration, hepatopathy and muscle damage. Sporadic bovine encephalomyelitis was considered a differential diagnosis. However, the chlamydia CFT test revealed a CFT titre of 16 (inconclusive).
Examination of Environment
Inspection of the environment within the immediate vicinity of the heifers revealed a number of identical plants of various stages of growth with large green leaves. Almost all of the plants showed evidence of being eaten with broken branches and leaves stripped. Photographs were taken of the plants (Fig 4 & 5). All these plants were located in a very small cluster on the riverbank. The owner was advised to destroy these plants as it was suspected that ingestion of these plants had caused the deaths and illness.
One litre of calcium, phosphorous, magnesium and glucose infusion was given subcutaneously to the surviving heifer. The producer was advised to provide adequate water and hay and to roll her onto her alternate side each day to minimise muscle damage.
The plants suspected of causing the deaths and illness were noted to be similar in appearance to Solanum mauritianum (wild tobacco) and initial prognostic advice was given to the owner on this basis. However, the predominantly coastal distribution of S. mauritianum did not fit with the location of this property and subsequent literature review and consultation with plant experts suggested that N. glauca was the more likely plant identification6.
The recumbent heifer finally got up on the tenth day, with no apparent ill effects. This is consistent with Everist3 who reports that animals which ingest a non-lethal dose may eventually stand and subsequently recover. Her recovery was timely, as euthanasia was planned if she had not recovered that day.
The pyridine alkaloids present in N. glauca, anabasine and nicotine, have both stimulant and depressant phases of action9. The clinical signs observed depend on the severity of intoxication, the degree of stress to which the animals are subjected and the time of observation after initial intoxication. Neurological signs may be missed as they can occur within a short time after ingestion7. The nicotinic receptors of the autonomic ganglia and the neuromuscular junctions, to which both anabasine and nicotine bind, are initially stimulated by an acetylcholine-like action. Stimulation results in weakness, tremors, and ataxia.5 This is then invariably followed by prolonged blocking of the neuromuscular junctions1. With ingestion of a lethal dose the persistent blocking of the neuromuscular junctions lead to progressive depression, paralysis, coma and death9. Death is often sudden once the animal begins to show depression and paralysis. Ultimately, death is ascribed to paralysis of the muscles of respiration1, 5. Toxicity from ingestion of N. glauca is also generally denoted by vascular and respiratory irregularites5.
In this case, the three dead heifers were not observed before their deaths so their clinical signs were unknown. On examination of the recumbent heifer neither vascular of respiratory irregularities were seen. It is postulated that if N. glauca was indeed the cause of death in three of the heifers and recumbency in one heifer, the latter may have ingested a non lethal dose.
Although this case is based on a presumptive diagnosis of N. glauca toxicity, a definitive diagnosis could have been made by testing tissues, urine or ingesta for the presence of anabasine7. A definitive identification on the plant could also have been achieved if a sample of the fertile (flowering) plant was sent to the National Herbarium of NSW in the Sydney Botanical Gardens.
N. glauca is considered unpalatable under normal conditions and is seldom eaten, despite its widespread distribution. Few cases of poisoning have been recorded. In situations where there is a shortage of feed such as drought, holding stock or transporting stock animals have been known to consume the plant and with rapid death following.
In cases of sudden death or those related to neuromuscular depression, N. glauca toxicity should be considered as a differential diagnosis, especially where soil has been disturbed. Care should be taken when droving or holding stock, to remove it from holding yards and holding paddocks and ensure stock have adequate feed available.