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This article was published in 1969-70
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Rock Fern Poisoning
R. J. CROSSING, B.V.Sc., Veterinary Inspector, Corowa.
Mortalities in Cattle during and after return from agistment in 1968.
INTRODUCTION
Periodically mortalities have been examined in cattle where the features are consistent with Bracken Fern Poisoning.
Confirmed or definite diagnoses have not been established but some investigators in areas where Rock Fern occurs have incriminated this plant.
Such diagnoses should be described as presumptive for two reasons at least:
1. There are no reports in the literature of the syndrome observed and the ingestion of Rock Fern.
2. No biological tests or feeding trials have reproduced the syndrome.
Rock Fern has widespread occurrence in N.S.W. and hence offers considerable opportunity for ingestion, accidentally or deliberately. However, the presumptive diagnoses made by several field veterinarians are worthy of consideration for the symptoms, duration of clinical signs, post-mortem findings and the period over which deaths occur bear a striking resemblance to Bracken Fern Poisoning but may occur in cattle with no exposure to Bracken Fern.
BRACKEN FERN AND ROCK FERN POISONING
Bracken Fern and Rock Fern occur in the Pteridophyta. Rock Fern (Cheilanthes tenuifolia and Notholaena distans) occur widely in N.S.W. The majority of reports of Rock Fern poisoning refer to Cheilanthes tenuifolia and describe symptoms and death in sheep with a brief mention of poisoning in calves. In sheep symptoms of depression, shivering, ataxia and diarrhoea are most common with congestion and haemorrhages in the intestines and congestion of the liver and kidneys on post-mortem. Death may be hastened by movement.
Bracken Fern Poisoning is also reasonably well documented with reports of poisoning in cattle and sheep. The disease produced following ingestion in cattle is reported to occur suddenly in catile two-eight weeks after exposure to and ingestion of the plant. Symptoms include depression, increased respiratory rate, temperatures between 105°F-109°F. dysentery or malaena and blood dripping from the nose, eyes and vagina. There are reports of nasolabial ulcers, haematuria, petechial and ecchymotic haemorrhages under the skin and visible mucous membranes and into the anterior chamber of the eye. Death occurs in one to three days. Losses may persist for up to six-nine weeks after removal from Bracken Fern.
On post-mortem, the striking feature is haemorrhages scattered throughout the carcass. There are haemorrhages, oedema, necrosis and sloughing of the gastro-intestinal tract. Infarcts and areas of necrosis occur in the liver, kidney and lung.
These symptoms and post-mortem findings are practically identical with those investigated on those occasions where there has been no known exposure to Bracken Fern.
The toxic factor in Bracken Fern has not been identified except to say that it is soluble in hot ethanol. It causes radiation-like changes to the bone marrow. These bone marrow changes are evident soon after feeding on Bracken Fern and appear well before symptoms. The effect on circulating cells is in three parts; first, there is a fall in platelets, secondly a fall in leucocytes, particularly polymorphs, and thirdly there is a terminal fall in R.B.C.s.
These changes produce three effects. The thrombocytopenia is associated with haemorrhage and loss of fluid from blood vessels, the leucopenia is associated with infection and a terminal Pasteurellosis has been mentioned, and finally there is an erythropenia associated with anaemia and respiratory distress. Haemorrhages and infection in localised areas of intestine are the early signs and similar manifestations occur in other parts of the body later.
INVESTIGATIONS
Between February and June, 1968, seasonal and pastoral conditions in the area between Lockhart and Deniliquin (New South Wales) were adverse and many landholders agisted cattle in the area between Nyngan and Narrabri for four or five months.
Large numbers were moved away from a multiplicity of owners. Some mobs were vaccinated for anthrax on arrival.
In June deaths occurred in these cattle on agistment. The Veterinary Inspector, Dubbo, investigated these and because of the prevalence of Rock Fern in the rumen of animals that died and because of other mortalities in the past associated with ingestion of Rock Fern, a presumptive diagnosis of Rock Fern poisoning was made.
Prompted by these losses and an improvement in seasonal conditions in southern N.S.W. owners made arrangements for their cattle to be brought home.
Most movements were made at night in uncovered transports in cold weather, early June, 1968.
On arrival home cows were very weak and generally in worse condition than before departure. Calves and yearlings surprisingly were in fair condition.
Weather locally at the time was cold and foggy. Lush grass was available and most owners provided hay in an attempt to improve body condition.
Deaths were reported in these cattle within three days of arrival home.
Only young animals (6 months-18 months old) were affected. Mortalities continued for three weeks.
Symptoms were depression, drops of blood from the nose and anus, mild signs of dehydration, slight swelling around the eyes and under the jaws, a harsh coat and a tucked up abdomen.
Temperatures ranged from 105°F.-108°F. Mucous membranes were pale and on occasions presented petechial and small ecchymotic haemorrhages. In a few cases rectal examination revealed blood in the faeces in the rectum.
Any superficial blood vessel cut to obtain blood for examination for anthrax clotted slowly.
Blood smears obtained ante- and post-mortem and examined for anthrax were negative.
Post-mortem findings were particularly uniform. A carcass would be in lateral recumbency. About 40 mls. of clotted or unclotted blood was present at the nose. Between 40-200 mls. of bright red, clotted blood was usually present at the anus, occasionally to form a long elongated mass. Ecchymotic haemorrhages occurred beneath the skin and mucous membranes. Ecchymoses were scattered widely throughout carcasses and were particularly common beneath mucous membranes of the respiratory and alimentary tracts and in sub-epicardial, sub-pleural and sub-serocal locations. Haemorrhages were regularly observed in lung, liver, and lymph nodes. Free blood was often observed in the rectum. Small ulcers were present in the abomasum or intestines. Livers examined were mottled and kidneys were pale. Swellings observed under the jaws and at the brisket consisted of straw coloured fluid that followed planes of connective tissue into deeper structures. Various areas were observed in muscle groups of accumulated straw coloured fluid and scattered haemorrhages in the connective tissue of muscle masses but these were never marked.
Bacteriology revealed haemolytic and non-haemolytic coliforms, a Proteus sp., a group B Salmonella and a Pasteurella sp. but organisms cultured were never consistent. No endotoxin was demonstrated in intestinal contents. Kidney and lung were normal on histopathological examination. Hydropic degeneration and mild centrilobular necrosis were observed in the liver. Non-specific inflammation was observed in brain and cord examined. Sub-epithelial haemorrhages were seen in mucous membrane and interstitial oedema and haemorrhages were present in muscle sectioned. Tests for arsenic and nitrite-nitrate poisoning were negative. FAT for Cl. novyi, septicum and chauvoei were negative.
MORTALITIES IN CATTLE DURING AND ON RETURN FROM AGISTMENT IN 1968
| Original Number | Composition | Deaths while on Agistment | Deaths after return to property of origin |
|---|---|---|---|
| 108 | Frisian heifers 9-18 months old | 25 | 12 |
| 80 | Frisian (sic) heifers 12-18 months old | — | 5 |
| 50 | Shorthorn cows and yearlings | 6 | 4 |
| 50 | Angus and Shorthorn cows and yearlings | 4 | 12 |
| 35 | Red poll cows and yearlings | 2 | 6 |
The similarity of the period of exposure to the Rock Fern, clinical signs, duration of symptoms, post-mortem these mortalities bear a striking similarity to Bracken Fern Poisoning.
Differential diagnosis
Anthrax in cattle generally occurs after a short period of clinical illness with pyrexia. Post-mortem examination reveals a failure of blood to clot, signs of generalised septicaemia and typical encapsulated bacilli can be observed in stained smears from peripheral blood. In these mortalities some mobs were recently vaccinated against anthrax, Blood smears collected from many animals that died were negative for anthrax.
Salmonellosis, Pasteurellosis and other primary bacterial infections were eliminated by detailed bacteriological examination.
A Haemorrhagic Enterotoxaemia is described in the U.S.A. and Great Britain, caused by Cl. perfringens type C, in calves 10 days old. Laboratory tests on intestinal contents revealed an absence of an enterotoxin.
Dicouimarol Poisoning and the Haemorrhagic Disease Syndrome bear some resemblance to this condition. There was, however, an apparent absence of any toxic substance and body temperatures of affected animals were markedly elevated.
Serum samples were collected from a range of animals but magnesium levels were all normal or near normal and eliminated Transit Tetany.
Histopathological examination of brain tissue was not suggestive of Bovine Malignant Catarrh.
Several features of Mucosal Disease such as the vulnerability of animals 6-11 months old and the high mortality rate are similar to this syndrome. The morbidity rate in this condition was high, in Mucosal Disease it is usually 2-5 per cent but reports have occurred where it has risen to 50 per cent. In both conditions, lesions occur in the alimentary tract with ulcers in the naso-labial area, however, in Mucosal Disease gross lesions are confined to the alimentary tract and are mainly erosive while in this syndrome a number of body systems were involved, including the alimentary tract and lesions were haemorrhagic and erosive in the alimentary tract and haemorrhagic in other locations. In Mucosal Disease beef cattle are more commonly affected than dairy cattle, there is profuse salvation a nasal discharge and watery diarrhoea (sometimes dysentery), skin lesions occur on the coronet and perineum, there may be cloudiness of the cornea, faeces are mucoid near death which occurs after four to 15 days. In this syndrome beef and dairy animals were affected. excessive salivation and watery or mucoid nasal discharges were not a feature, faeces were consistently blood stained or tarry, there were no skin lesions or changes to the cornea, faeces in the terminal stages were bloodstained and animals died after one to three days.
TREATMENT
A wide range of antibiotic and supportitive therapy was attempted but results were uniformly disappointing.
ACKNOWLEDGEMENTS
As stated earlier it was stated that the syndrome observed could result from ingestion of Rock Fern. There are many further areas for investigation both in actual cases and under experimental conditions to allow a definite diagnosis to be established.
Details of these investigations are recorded because of the unusual features observed and the absence of similar reports in the literature except after ingestion of Bracken Fern. It is hoped this presentation may be useful and provide a basis for further investigation should the condition be encountered in the field again.
Details supplied by Messrs. P. S. Green (Veterinary Inspector, Dubbo), P. J. Fenaughty, B.V.Sc., Deniliquin, and E. S. Rogers (Veterinary Inspector, Deniliquin), are acknowledged. Mr. D. J. Walker (formerly District Veterinary Officer, Narrandera), assisted in these investigations and made available the colour transparencies used in this conference.