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This article was published in 1961
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.

Anthelmintics for Sheep

A BRIEF REVIEW

S. P. HEBDEN, B.V.Sc., Special Veterinary Research Officer, Glenfield

The use of anthelmintics plays such an important part in sheep management that new products are being produced constantly for this purpose. Competition for sales is strong and some of the bigger Stock Medicine firms employ chemists and veterinarians, and also maintain experimental flocks to test and evaluate chemicals produced, for the most part, overseas.

During the last two years quite a number of such chemicals have been tested by the C.S.I.R.O. and at this Research Station, but most have failed, for one reason or another, to measure up to the high standard set by Phenothiazine which for twenty years has maintained supremacy in this field. It now seems, however, that this position is being challenged seriously by more than one synthetic compound, highly efficient over a broad spectrum and relatively non toxic. At the same time the reported appearance of parasitic resistance to Phenothiazine in the U.S.A. (suspected to exist also in this country) and recent reports of losses, both in New Zealand and Australia, following its use have stimulated the search for a better anthelmintic. As regards phenothiazine poisoning the number of cases reported are very few, and bearing in mind the quantities used in this country and that we have never been able to produce this condition in healthy sheep with normal dosing it must still be regarded as a very safe drug to use.

Before any product can take the place of Phenothiazine it must prove to be highly efficient against the important sheep nematodes, both mature and immature, easy to administer without the necessity of pre-swabbing and relatively non-toxic. It should also be reasonably priced.

The classification adopted in this short review can only be regarded as broad with the object of brevity. Some chemicals such as Quinazine toluene sulphonate, Dithiazanine iodide, Dow E.T.57 and Diaquone have been excluded as no further work with them is envisaged. They have given some good results, but more recent introductions appear to be superior.

GROUP I — ARSENIC, COPPER, CARBON TETRACHLORIDE, NICOTINE SULPHATE

These drugs in wide use, before the advent of Phenothiazine, either singly or in combination are still widely used today. They are not superior to Phenothiazine for any worm parasites, with the exception of fluke and tapeworms, but are cheaper and easier to handle. They are known so well that further comment is unnecessary.

GROUP II — THE ORGANIC PHOSPHATES — NEGUVON, ASUNTOL, KEMPAK

As a group these anthelmintics are relatively toxic and restricted in anthelmintic efficiency. For the treatment of worms other than Haemonchus pre-swabbing with 5 - 10% copper sulphate solution is necessary. Neguvon is now only recommended for Haemonchus at the lower dose rate (55 mg/kg.) and Asuntol which will shortly be on the market has also a restricted use at 8 mg/kg. Kempak is now being distributed by Nicholas Pty. Ltd., after fairly extensive trials. It is available as a 35% w/ oil based solution with a dose rate of 50 - 200 mg/kg, and at the lower rate is highly effective against Haemonchus.

The antidote for all three is Atropine Sulphate at ¼ to ½ gr. intramuscularly

GROUP III — BROAD SPECTRUM HETERO-CYCLIC COMPOUNDS PHENOTHIAZINE, FRANTIN, THIABENDAZOLE, PROMINTIC

Phenothiazine is now produced in a very pure (92%) and fine (18,200 cm²/g. by A.P.) form. Recent tests have shown the new product to be more efficient against Ostertagia and Trichostrongylus species including the immature forms. Toxic effects appear to be related to dehydration and there is no evidence that the very fine and pure product is in any way more toxic.

Frantin or Bephenium hydroxynaphthoate because of its high price (about 2/- per dose) is used only for the removal of Nematodirus for which it is highly efficient. It has also given excellent results against Haemonchus and Ostertagia species both mature and immature, and against Oesophagostomum at the higher dose rate. It is recommended especially for parasitic gastritis in unweaned lambs notably where Nematodirus is present.

The dose rate is 250 - 600 mg/kg., treatment being three doses at three-weekly intervals. There have been occasional reports of toxic effects at the higher dose rate.

Thiabendazole or MK 360 has recently been produced by Merck, Sharp & Dohme Laboratories, U.S.A. and is now under test. Early trials at Glenfield have demonstrated 100% efficiency for Haemonchus, Trichostrongylus and Oesophagostomum species and about 90% for Ostertagia and Nematodirus. In toxicity trials sheep given up to twenty times the therapeutic dose showed no ill effects. Formulated as a suspension the dose of which is 1 oz. per 100 lb. body weight for broad effect the actual therapeutic dose for different parasites has not yet been determined. It should be available in about twelve months at a cost similar to that of Phenothiazine.

Promintic is a pyridine derivative produced by I.C.I. and not as yet available in Australia. Most of the trials have been carried out by I.C.I. and the C.S.I.R.O. and early reports indicate its high efficiency over a broad spectrum. Formulated as a solution it may be administered orally or subcutaneously.

GROUP IV — MIXTURES

Recent introductions are mixtures of two types, those in which one chemical acts synergistically on another and those in which chemicals are simply included for their selective action against certain species.

An example of the first type is "Coopex" produced by William Cooper & Nephews Pty. Ltd., but not yet available. It is a mixture of Phenothiazine and Coroxon, an organic phosphate closely related to Asuntol. The dose rate is 200 and 2 mg/kg. respectively and claims are made that it will give a 99% reduction of Haemonchus, Trichostrongylus and Ostertagia species. Reports of independent trials now in progress are awaited with interest.

Two examples of the second type are quoted, both contain Piperazine for the control of Oesophagostomum infection.

"Eludon" is a mixture of arsenic, piperazine and copper sulphate formulated by Boots Pure Drug Co. Pty. Ltd. for the control of Oesophagostomum and supplementary control of Haemonchus and Monezia. It is designed for use in Northern N.S.W. and Queensland. No official reports of results achieved are available although some trials were carried out in Queensland by K. Hughes, a field research officer, of the University at Brisbane. The dose given for a "grown" sheep is 1 fl. oz. which contains 4 gms. of Piperazine. The dose of this drug given by the British Veterinary Codex 1953 is 200-300 mg./kg.

B.I.O. All Purpose Drench combines piperazine (40%), copper sulphate (7.2%) and nicotine sulphate (31.6%). No official reports of its value are available but attention is drawn to a report from Gordon (1955) who found that a similar mixture produced severe toxic effects.

GROUP V — ANTHELMINTICS FOR FLUKE

Carbon Tetrachloride has been used for the control of fluke in sheep for many years. The cause of losses following this treatment is still not understood fully. By injection the dose is 1 c.c. per kg. without addition of liquid paraffin and it has been found recently that a dose of 4 c.c. per os is required for the elimination of the parasite.

Freon 112 or Tetrachlorodifluoroethane will be introduced shortly as an alternative treatment for fluke. It will be formulated by Troy Laboratories with the name of "Troy-Fron 112" the oral dose being .05 g. per lb. or 10 c.c. of the formulated material per 100 lb. body weight. The cost will be about 4d. per dose. Relatively non-toxic it is recommended for treating sheep in areas where losses from carbon tetrachloride are common. Its effect on Haemonchus is unknown.

REFERENCE:

Gordon, H. McL. (1955) — Aust. vet. J. 31:52