Sustainable control of internal parasites in ruminants

Abstract

Internal parasites have been a problem for animals, probably since the dawn of evolution. However, domestication and the constraints we impose on animals, particularly ruminants, by restricting selection of forage and grazing range, load the dice very much in favour of the parasites. This is a continuing problem of most livestock we have to deal with. This text should inform the reader that this is not a situation which has quick solutions or easy answers, but despite this, progress in the control of parasites is being made. Knowledge of the parasites and of the host animals' responses to parasitic challenge will help us to keep pace with this progress. Also it is intended that the Animal Industries Workshop should go some way to explaining the principles of sustainable control. The total reliance we placed on the 'miracle' worm drenches which became available from the early 1960s has resulted in our neglect of other management factors which, if utilised, should reduce our total dependence on these 'wonder' drugs. With the development of resistance to these drugs by the parasites and the spectre of meat and milk residue problems, the time is now opportune for re-examination of control measures. The purpose of the workshop and this book, which is derived from papers presented during the workshop, is to present up-to-date information which can be used to inform and upskill all concerned with the management of parasite problems. International specialists such as Quintin McKellar, Peter Waller and Ian Barger have contributed their considerable knowledge and understanding of the anthelmintics available, how they work, how anthelmintic resistance can arise and of the place long acting preparations and mixed anthelmintics have in control programmes. Other writers have addressed factors such as the extent of parasitism in New Zealand livestock, the life cycles and infectivity of these parasites in livestock, and the effects of nutrition in influencing the outcome of infection. Selection of resistant animals within breeding programmes and the acquisition of natural and artificial immunity are also included. Management practices to control gastrointestinal parasitism each have limitations and this is discussed, as is the use of computer models. These papers show that the situation is not hopeless, but the sustainable control of internal parasites of ruminant animals will require sensible drug usage, genetic selection of resistant livestock and use of alternative grazing and possibly nutritional management strategies.