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This article was published in 1949
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
HELIOTROPE POISONING IN SHEEP
J. C. KEAST, B.V.Sc., P.P. Board's Veterinary Research Officer. Glenfield.
Many sheep losses which in the past have been attributed to Toxaemic Jaundice have been due to poisoning by the plant Heliotropium europaeum.Although extensive heliotrope grazing has been shown to favour a higher incidence of the haemolytic type of jaundice or copper poisoning, the large majority of the losses that have occurred in the Murray Valley have been due to a liver damage resulting from an alkaloid, lasiocarpine, which is present in the plant.
Heliotrope is a summer growing annual weed which appears to have spread considerably in many areas of New South Wales during the last 10-15 years. With summer rains the plant grows profusely in fallows, natural pastures and to a considerably less extent in stubbles; but if summer rains do not occur it may be relatively inconspicuous in grazing areas. The plant does not appear to be attractive to sheep when other green feed is available, but it occurs as the only green plant in an otherwise mature grassy pasture it is eaten readily. It also is eaten extensively in the dry state.
Heliotrope poisoning is common on properties in the Murray Valley, particularly in seasons when summer rains have resulted in a heavy growth of the plant. In this area the summer rains in 1946-47 and 1947-48 led to extensive grazing on the plant, with resultant heavy losses in 1947 and 1948. In the latter year many properties lost up to 30 per cent. of the entire breeding stock while in some individual flocks the losses were over 50 per cent. Although some losses occur following a single exposure to the plant, the liver damage is progressive and considerably heavier losses can be expected if seasonal conditions favour a second exposure to the heliotrope. It is not known to what extent heliotrope poisoning occurs in parts of the State other than the Murray Valley, but it is extremely likely that "jaundice" losses in the Berrigan, Wagga and Gundagai districts are due to the ingestion of this plant.
Type of Animals Susceptible. British breeds and their crosses appear most susceptible and it is not known whether the comparative non-susceptibility of Merinos is due to a definite resistance or whether, as more selective grazing animals, they ingest less of the plant. There is an age susceptibility, but this is dependant to a large extent on the availability of the plant during the life of the sheep. Thus, with good heliotrope summers in 1947 and 1948, it was found that losses in maiden ewes in 1948 were just as severe as in older animals, because they had had two successive exposures to the plant. Rams and wethers appear to be just as susceptible as female animals provided they have similar opportunities to graze the plant.
Symptoms. The nature of the disease varies considerably in different seasons and in different flocks. Although most of the grazing on heliotrope occurs from December to April, it is usual to find the highest death rate between June and August; sometimes extending to November. This explains why purchased sheep often commence to die some months after their removal from an affected property. Odd sheep can die, of course, while grazing on the plant, but the peak of the losses generally occurs in the winter and spring months. Some animals simply may be found dead without showing previous signs of ill-health, while others may be sick for a few days before dying. A varying proportion become sick and linger for some weeks or even months. In these eases the sheep show a very rapid and severe loss in bodily condition and may exist for some time in an emaciated state. Sick sheep may be jaundiced or may show no clinical evidence of icterus. The percentage showing clinical jaundice may vary between 20 per cent. and 80 per cent. Of the jaundiced cases, many are of the non-haemolytic type in which the urine remains free of blood pigments. The varying, and often low, proportion of cases showing clinical jaundice often makes field diagnosis difficult; particularly when only one animal is available for autopsy.
Post-mortem Findings. The appearance of the typical haemolytic jaundice case is well known. When icterus has not been observed clinically it is possible that some cases will show a lemon tint or slight muddy of the carcase, indicating the presence of some circulating bile pigments, while in others jaundice is absent. The liver varies between a khaki and orange colour, is often enlarged and sometimes fatty. In the wasting type of case, the liver often is shrunken, fibrosed and hob-nailed. The kidneys may be congested. Lesions of enteritis are not infrequently present in both the small and large intestines, and at times may be sufficiently severe to result in the presence of free blood in the lumen of the gut.
Prevention. The ultimate aim must be to eradicate this noxious plant from the property. This will not be an easy matter and probably will be a long range project. Experimental work will be commenced in the near future on various methods of controlling the plant. In the meantime, stock losses must be prevented by denying susceptible sheep access to the plant in seasons when it flourishes.
Until the recent demonstration of the toxic properties of heliotrope, little attempt had been made to prevent stock grazing the plant. It is well known that sheep will fatten on it without showing any immediate ill-effects, while it also has been found to keep sheep alive in periods of drought when little other summer feed is available. Many stockowners have grazed the plant heavily on fallow land in an attempt to keep the fallows clean. All these practices are dangerous, and despite the apparent immediate benefits it must be realised that the alkaloid present will cause damage to the liver cells and ultimately the health of the sheep will suffer. The prevention of heliotrope grazing is a management problem which must be tackled by each landholder so suit his own property.