Information issued recently by the Chief of the Division of Animal Industry advises that doses of 4 mls. of Carbon tetrachloride (20 mls. of a single-strength mixture) have been found effective in treating cases of Acute Fluke infestation; and that this comparatively very large dose is not any more likely to be injurious to sheep than is the 1 ml. dose which has been used for many years now in treating the chronic form of the disease.
It is several years since Mr. Hugh Gordon of the C.S.I.R.O. McMaster Laboratory expressed the conviction that mortality in sheep following drenching with Carbon tetrachloride is much more a matter of susceptibility than of dosage; and that in fact if an animal were not affected by a 1 ml. dose it probably would not succumb to a dose even ten times greater. Nevertheless it still is a fact that when the larger dosage is suggested to sheepowners involved in a mortality from Actue Fluke the usual result, particularly on properties where mortality following ordinary dosing has occurred, is a more or less violent protest from the owner. For this reason it is thought that some actual experiences may be helpful.
The year 1950 will be well remembered as the wettest year in the recorded history of our State, and the Moss Vale District was no exception. Ninety (90) inches was the official record in the town and throughout the highlands it was at least that; to much higher, reaching what is thought to be the climax in one unofficial registration of 150 inches. As could be expected, this extreme wet was ideal for the development of the fluke snail; and believe me that development of this snail really was high. The floodings that occurred following the heavy falls of rain were frequent; consequently the snail was distributed to parts of the District where its presence was unknown previously, and as the hills were just as wet as the hollows the snail was everywhere. It was feared that the fluke pick-up the following year would be heavy and those fears were not unfounded. The acute fluke outbreak which started in May, 1951, was the worst in the experience of the writer and nothing equalling it ever before had been seen in the highlands. The only outbreak ever seen by the writer to approach this one was on the watercourse in the north- western districts in 1925 or thereabouts. Hardly a flock of sheep escaped and every liver seen for at least four months following May was carrying a heavy fluke burden. During the outbreak the livers of sheep examined were full of the immature fluke and in one count undertaken 1,000 adult fluke were counted; while the count of immature fluke was unfinished at 6,000 in the same liver. The known remedy was given; the dose rate being the usual 1 ml. of Carbon tetrachloride to 4 of paraffin. This had no effect and the dose was increased to double that quantity; again without any success. Deaths continued. The position was desperate and becoming more so, and a desperate remedy appeared to be the only line of action.
After consultation with the District Veterinary Officer, the Principal Research Officer at Glenfield and Mr. H. Gordon of the McMaster Laboratory, it was decided to increase the dose rate and a double-header of double-strength was given; that is, 4 ml. of Carbon tetrachloride in 16 ml. of paraffin. The results were amazing. Where the death rate on one holding was approximately 200 sheep a week, the outsize dose stopped the mortality in three days and no toxic effects were seen. Following this experience on one property the increased drench not only was given on one holding, but on many; and again without any toxic effects.
So much for the lesson from the major outbreak on the Southern Tablelands in 1951, but as a matter of fact some experience with the larger dose was gained in a neighbouring District, as early as 1947. On that occasion losses from acute fluke resulted apparently from some quality in the creek and/or spring water which prevented the usual action of bluestone in destroying the host snail. The owner sought help from the McMaster Laboratory and on Mr. Gordon's advice administered 10 mls. of a double-strength Carbon tetrachloride; using first a small trial flock. The details in this case were:—As a preliminary precautionary measure 50 ewes forward in lamb were treated, and as no deaths had occurred in these seven (7) days later, a further 600 were treated at the same dose rate. Three days later the balance of the sheep on the property were treated similarly; with the exception that the dose given to sheep up to the age of about 10 months was 7.5 mls. only. The total number treated was approximately 2,000; comprising Merinos, Border Leicesters and some crossbreds. The treatment was considered to be completely successful, and entirely without untoward effect.
In the same District during the late autumn/early winter of 1951 losses of at least one per day were occurring in a flock of 350 first quality Merino ewes in about mid-pregnancy; and at that time worth very big money. On post-mortem there were the usual, and very obvious, indications of an acute fluke infestation and the owner was persuaded against his natural inclination to treat the mob with five (5) times the normal dose of Carbon tetrachloride. There is no doubt that this owner accepted the recommendation with a profund "kill or cure" attitude; but he did use half a dozen of the "tail" of the mob as a trial. Again the treatment was a complete success; one death only occurring after drenching.
The fatalistic outlook of the owner in the last case had some real foundation. His property is situated in accepted "fluke country"; so that although he has been compelled to use Carbon tetrachloride (in ordinary dose rates) for many years, on each occasion an after-drenching loss ranging from at least 10% was accepted as the normal expectation.
It may be of some significance that the property is situated also in a known calcium-deficient area; and that prior to the uneventful use of Carbon tetrachloride the sheep had access to for at least 3 weeks, and were consuming readily, a calcium-rich lick consisting of ground limestone and coarse salt.
It is said with some truth that "there has to be a first time", but it has been said also that due regard being paid to weather conditions and food intake, Carbon tetrachloride poisoning has not occurred yet in sheep receiving an adequate supply of calcium.