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This article was published in 1954
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Heliotrope Poisoning in Sheep
SOME FIELD OBSERVATIONS
G. CHARLES, B.V.Sc., Inspector of Stock, Forbes.
As there is a large area of the district where Heliotropium europaeum makes prolific growth following summer rains, and as summer climatic conditions are frequently such that there is no green feed available to sheep, ample opportunities arise to observe cases of heliotrope poisoning, and the following notes have been compiled as being of interest.
CAUSAL PLANT :
The plant is a summer annual which flourishes on fallows, stubbles and land which has been denuded of grass and useful herbage by rabbit infestation or overstocking. Most frequently it is seen as a small plant up to 12 inches high, having olive green leaves, somewhat hairy and bearing an inflorescence made up of small white flowers closely packed. These flowers give place to numerous small green seeds giving the stem the appearance of a green caterpillar, hence one of the common names, "Caterpillar Weed". It is known also as "Mother of Millions" or "Wandary Curse". The plant is a prolific seeder and also makes vigorous second growth if it has been grazed back. It appears to commence seeding very early in its growth and continues almost throughout its whole life. It is susceptible to frosts and so it is not seen from late autumn on until early summer.
TOXIC CONSTITUENTS:
As reported by the Enzootic Jaundice Investigation Committee (1952), the alkaloid pattern of the plant is complex. However, heliotrine and lasiocarpine and their N-oxides have been isolated and their effects on rats have been studied. Repeated small doses of heliotrine injected into rats over four to six months bring about pathological changes in the liver closely resembling those seen in sheep dying from heliotrope poisoning. Similar experiments, as far as they have progressed, with lasiocarpine have failed to produce chronic liver damage but have produced acute haemorrhagic changes. Heliotrine and lasiocarpine are labile and are believed to be almost completely destroyed in the rumen by bacterial action, but when sheep are poor and the gastrointestinal tract is relatively empty, passage of ingesta through the rumen is much more rapid and quantities of the alkaloids may escape destruction. The N-oxides are water soluble and non-toxic. Because of their solubility they are believed to pass more rapidly from the rumen, and are reduced to the Toxic forms in the animal body, thus accounting for the more chronic lesions. In view of the lesions produced by lasiocarpine, one wonders if this alkaloid may be an anti-Vitamin K factor, but to date there is no knowledge in this regard.
PREDISPOSING CAUSES:
Given adequate feed, either pasture or handfed, sheep do not eat the plant voluntarily, but all too often in this District summer conditions are such that no good pasture is available, nor is hand-feeding practised, and Heliotropium europaeum is the only green grazing available. Apart from climatic conditions the paramount predisposing cause is the method of husbandry adopted by the mixed farmers of the District. It has been the practice here for many vears, as it is elsewhere, to depasture the sheep on the fallows, which serves a twofold purpose; firstly that of keeping the fallows free of excess weed growth and secondly, of enabling the sheep to obtain a green pick, often of dubious value, following summer rains. Such rains, of course, favour heavy growth of heliotrope. Two seasons grazing appears necessary before symptoms occur.
SHEEP AFFECTED :
Losses are always heaviest in pregnant ewes, followed by ewes with lambs at foot; while some deaths occur in dry sheep. As the syndrome is linked essentially with nutrition it is obvious that pregnant ewes, about half-way through pregnancy and on a declining plane of nutrition, are most susceptible. Crossbreds and Corriedales are very susceptible and in one outbreak 30 per cent. of the latter breed succumbed over a period of six months. In one flock of Crossbreds the mortality was 19 per cent. of a flock of 500 ewes over a five months' period. Merino sheep are affected only rarely. Age appears to have little influence on susceptibility except where it precludes two grazings, although one case was seen in Romney Marsh weaners, 10-11 months old. where there was evidence of only one grazing having been made. Bodily condition has little bearing as deaths have been seen in fats, stores and poor sheep, but in all cases there was the common factor of a declining nutritional plane.
SYMPTOMS :
Cases of heliotrope poisoning appear to fall into three different types, which for convenience are called acute, sub-acute and chronic. Symptoms vary somewhat in all three types.
Acute cases almost invariably occur early in the season when the plant is growing vigorously, and are seen in fat pregnant ewes, fat no doubt because they are the best foragers and ingest a greater amount of the plant. In these cases jaundice is present to a greater or lesser degree, the liver is engorged and not otherwise macroscopically altered, and there is marked evidence of acute haemorrhagic changes, especially in the small intestines and heart. Death is usually fairly rapid in these cases, occurring 36-48 hours after the affected sheep is first seen. These cases would appear to result mainly from the effects of lasiocarpine, but whether early growth stages of the plant contain a higher proportion of the alkaloid or the sheep eat more of the plant has not been determined, but probably a greater intake of the plant results in more lasiocarpine escaping destruction in the rumen and in higher amounts of the N-oxide being ingested.
Sub-acute cases occur in mid-season when the plant has reached its maximum growth, and the sheep are in store condition. Again pregnant ewes or ewes with lambs at foot are affected and the deterioration in bodily condition is due to lack of feed. In these cases jaundice is pronounced and the haemorrhagic lesions less marked. Liver changes are obvious, there being cirrhosis and invariably the organ is almost a yellow ochre to orange colour. There is a longer period of clinical sickness and death may not occur for three to four days. Death appears to be due to the combined effects of heliotrine and lasiocarpine.
In late autumn and on through a dry winter the so-called chronic cases occur. By this time sheep are in poor to store condition and ewes have lambs at foot. In these cases jaundice is often not apparent, the haemorrhagic lesions are very often absent and the liver is orange coloured, cirrhotic and often "hobnailed". Death does not occur usually for five to seven days. These cases appear to be due almost entirely to the prolonged absorption of heliotrope. Deaths have been seen up to three months after removal from access to the plant, provided pasture conditions remain poor.
In two individual cases only, a terminal haemolytic crisis with consequent haemoglobinuria has been seen, and in these cases the kidneys were enlarged, bluish in colour, as seen in chronic copper poisoning: thus confusing diagnosis. However, histological examination of the liver confirmed heliotrope as the cause of death.
EFFECTS OF DRIED PLANT :
Towards the end of a long dry spell the plant dries off considerably but retains its leaves until the first frost. At this stage "old timers" in this District depasture dry sheep on the plant, apparently with no ill-effects, and this has been their custom for many years. Lack of toxic effects is due most probably to the dry sheep being in fair condition with full gastro-intestinal tracts, hence the plant is retained in the rumen for longer periods, so result ing in greater destruction of the alkaloids. Also, it is possible that the alkaloid content would be at its lowest level at this stage of growth.
MORTALITY RATE:
At the beginning of a season the mortality rate is often high and may reach five or six per day. One or two per day are common losses and these may continue for some time. Overall losses range from 5 per cent. to 30 per cent., the average being about 10 per cent. Losses tend to dwindle and reach about one or two per week and these may continue, subject to seasonal conditions, over a relatively long period. Undue exertion or handling will result in a temporary increase in the death rate. Even when sheep are moved to paddocks free of heliotrope and fed on adequate diet deaths may not cease entirely, but may continue at the rate of two or three per month
PREVENTION:
Until such time as owners realise more fully that a change in their husbandry methods is essential to avoid fallow grazing, and that supplementary feeding is an essential factor in maintaining an even plane of nutrition, prevention cannot be achieved. Where supplementary feeding is practised little or no trouble is experienced. The practice of sowing a light seeding of rye grass or lucerne with the wheat crop is of value as it provides useful grazing in the stubbles.
Control of the plant may be achieved by intensive, frequent cultivation, but this is not always possible when the season is dry, nor does the idea appeal to farmers generally. Serious consideration must be given to control of the weed but until such time as a suitable, efficient and economical method can be evolved, it is obvious that prevention of losses depends entirely on three points:
1. Wherever possible avoid grazing the plant.
2. Adequate hand-feeding, commenced early enough to prevent the developing of hunger in the sheep, and continued so long as the plant is present.
3. The provision of summer grazing such as Japanese millet, lucerne,etc.
REFERENCE:
Investigations into the Etiology and Control of Enzootic (Toxaemic) Jaundice of Sheep (1952) Aust. vet. I. 28: 309.