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This article was published in 1951
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
Rock Fern Poisoning in Sheep
K.V. BYRNE, B.V.Sc., Inspector of Stock, Young.
Although it would appear from literature on the subject that a very big proportion of weeds of this State are poisonous or suspected of being poisonous to stock, serious mortalities from this cause have not been common in the writer's experience. If it is true that such losses are infrequent, such probably is due to the fact that stock know instinctively what is good to eat and what is not.
However, in March of this year (1951) a mob of 400 Merino wethers near Cowra did not supply such sagacity when introduced to Rock Fern (Cheilanthes tenuifolia) for the first time.
These sheep had been drenched with Bluestone and Nicotine sulphate and placed in a top hill paddock which contained a poor supply of feed consisting of old, dry, coarse grass. Although he could see the sheep in the distance, the owner actually did not go into the paddock for another week. He then found that 50 of the wethers were dead, with another 40 or 50 sick. The chief symptoms were staggering, a discharge from the mouth and a profuse greenish diarrhoea. Affected animals did not eat. He immediately moved the sheep into a lower paddock, but deaths continued until the total losses at the time of the writer's visit five days later numbered 80. At this time, however, the position was beginning to improve; the mortalities having almost ceased, with no fresh cases developing.
The paddock to which the sheep had been moved had a river frontage; with much better feed, including a green pick.
As there was no recently dead animal at the time, a typically sick one was destroyed for post-mortem examination. About 30 sick sheep were seen but most appeared to be recovering, and the one killed, which was one of the worst, was fairly strong.
The examination disclosed a not very marked gastro-enteritis, but one formed the impression that the animal had been recovering from a more severe attack of that condition. The gall bladder was markedly distended, and the duodenum was filled with a greenish-tinged fluid. The contents of the remainder of the alimentary tract were liquid. The kidneys had a very swollen appearance.
The owner had bought the sheep only a few months previously, and this was the first occasion that they had been put in the top paddock. Rock Fern does exist in other paddocks on the property, but these also contain other green feed, and it is considered that the sheep did not eat the Fern in the other paddocks.
It was considered likely that the losses were due to Rock Fern poisoning, and appropriate specimens were forwarded to Glenfield Veterinary Research Station. Subsequently, a report has been received from the Station, and this stated:—
"The liver showed slight lesions of fatty degeneration, and the kidney showed a chronic interstitial nephritis. The abomasum and small intestine showed sub-acute inflammation."
The rumen contents were forwarded to the Botanist, and his report read as follows:-
"The rumen contents forwarded for examination consisted of fibrous matter with a considerable quantity of stems of Cheilanthes tenuifolia and traces of Casuarina species, Heliotropium and a species of Chenopodiaceae or Amaranthaceae."
The plant specimen forwarded was identified as Cheilanthes tenuifolia; and it appears that this plant was responsible for the mortality.
The landowner concerned had only just recently taken up the property, but he understood from the previous owner that there had not been extensive mortalities in sheep on it in the past. However, it appeared from neighbours' reports that losses from time to time have occurred in the locality, and the plant is recognised by them as poisonous. It also seems evident that, as is commonly the case with poison plants, losses are less frequent in sheep which are accustomed to Rock Fern country than in introduced stock; and that even these will not eat the Fern if adequate supplies of other feed are available.