Modern drugs for worms highly regarded

Press, 18 February 1977, Page 7

Modern drugs for worms highly regarded

The modern drugs that were available for killing worms were quite fantastic — the best were more active in general than an antibiotic—Dr 11. M. (Hugh) Gordon, who is president of the Australian College of Veterinary Scientists, said in Christchurch this week.

Dr Gordon, who is here for the annual conference of the New Zealand Veterinary Association, is a world authority on the worm parasites of sheep on which he worked at the McMaster Laboratory of the division of anima! health of the Commonwealth Scientific and Industrial Research Organisation before he retired in 1974. As well he was a parttime lecturer at the Veterinary School at the University of Sydney doing the ■whole course on parasitology from 1937 to 1970, and in his retirement is still a part-time lecturer and demonstrator there. In tnis roie he came to know many New Zealanders when they trained in Sydney to become veterinarians. Dr Gordon said that the notable thing about modern drugs used for parasite

materials, and this was in the nature of a warning or writing on the wall. While in practice this was not serious yet, he said that cattle tick control in the Northern Territory’ of Australia was in jeopardy because of the insect developing resistance and the genera] recommendation was to introduce some Brahman blood into a herd, where selection had not been done in British breed herds for animals that were more tick resistant. Immunising animals against parasites was something on which a great deal of work had been done and it had promise, but so far there was really only one case where it had been successful and that was with lung worm of cattle. Use of irradiated larvae with cattle had resulted in perfectly sterile females but as yet it was a very expensive process and not necessarily effective everywhere. A process had also been developed for immunising dogs and sheep against tapeworms, which showed a certain amount of promise where the incidence of such worms was high to bring down populations to a level where other methods of control might be introduced, but it was also relatively expensive in comparison with not feeding raw offals to dogs. Dr Gordon said that pioneer work had been done in the C.5.1.R.0. in Australia in the epidemiology of parasites of sheep and cattle. This involved the whole study of such prob-

lems in the whole flock or herd, which was most important in the context of large animal veterinary practice. With worm parasites they had to deal with whole flocks with all of the animals affected and often with cattle as well because of cross transmission. W’hen highly effective drugs became available he said that they had been able to carry out intensive treatments which allowed them to measure better the loss that was attributable to parasitism. In most cases the result of intensive treatments was a reduction in the numbers of parasites and even where the costs and benefits were similar he said that the parasites could still be causing a loss and there was then a need to find a cheaper treatment. In Victoria he said that the C.5.1.R.0. had treated sheep every two weeks for parasites and this had remained profitable while prices for wool remained at high levels, but tended to be “dicey” when prices fell. Like milk, he said that wool production was highly sensitive to such effects. However, there were a number of spin-offs from such treatments, where sheep were virtually worm free. They did not scour and there were consequently no dags so they did not have to be crutched and they did not get fly strike. And at the end of the trial instead of there being up to a 20 per cent mortality they all survived. Where in some trials there had been losses Of up to 15 to 20 per cent of young ewes, Dr Gordon said that this involved also a loss of mothers of future lambs and in the ease of stud sheep a loss of genetic potential as well. Dr Gordon noted that losses avoided through such treatment could be just as useful as profitability that was gained.

Questioned about claims made by manufacturers for anthelmintics, based on trial work, which were sometimes viewed with suspicion by farmers, Dr Gordon said that this suspicion was often related to earlier recommendations that treatments should be kept to minimal levels and consideration of the labour costs involved, but thought had to be given to the point whether labour not put into drenching would be used more profitably in some other d’ay and quite often it could be shown that drenching would be the most profitable use of labour. However, claims were made for anthelmintics that were extravagent and it was often a question of terminology. But Dr Gordon said that one firm had done pioneer work on a property of its own in the North Island with an intensive system of treatment known as “suppressive treatment” to keep reinfestation at a minimum, and this had since been repeated in Australia on summer rainfall country in the northern tablelands and in winter rainfall country in western Victoria, and this was open to all interested people, including farmers, university and Government people and private veterinarians to go and see and to examine the figures. These were quite remarkable ex-> periments and were all above board.