Prevention and control of parasitism in livestock

Kalyan Sarma
The control of parasites, both ecto and endo, is one of the biggest challenges faced by livestock farmers in today’s world. Parasite resistance to chemical treatments is increasing and consequently, the availability of effective chemical treatments is declining. Control of these parasites is now becoming a serious concern in industries, due to the widespread and rapid development of resistance to chemotherapy. The broad-spectrum drugs (anthelmintic) used in the control of parasites fall into just three classes viz., the benzimidazoles, imidothia-zoles and macrocyclic lactones.
This is largely the result of more-or-less complete reliance on anthelmintic for parasitic control. Any specific parasite control measure may be unsustainable when used separately. For successful worm control measure depends on a combination of different measures rather than solely depend on anthelmintic. The effective non-chemical methods for parasitic control are grazing management strategies and biological control. These should form part of integrated nematode parasite control programmes for grazing livestock to maintain long-term sustainability.
At present, the non-chemotherapeutic control of pasture related infections is based mainly on grazing management strategies. Preventive strategies, where young, previously unexposed stock, are turned out on parasite-free pastures, can be used for grazing first season dairy heifers. Repeated moves of the cattle or alternate grazing with other species, is one of the strategies for effective control of nematodes. High stocking rates seem to be an important risk factor. Methods available for the control of the parasitic infections are mainly based on chemical treatment, non-chemical management practices, immune modulation and biological control. Various arms of Integrated Worm Management involving anthelmintic management and covering Targeted Selected Treatment system, grazing management, nutritional management, biological control, Phyto therapeutic control are now available for widespread adoption.
Parasitic diseases are a global problem and considered as a major obstacle in the health and product performance of animals. These may be due to endo-parasites that live inside the body, or ectoparasites such as ticks, mites, flies, fleas, midges, etc., which attack the body surface. Parasitic diseases are one of the greatest disease problems in grazing livestock worldwide. Parasite infestations may cause a significant economic loss because they retard growth, impair reproduction, lower milk production and may even cause death in infected animals. Also, some domestic animal parasites threaten the health of the human population.
Malaria and intestinal worms are parasitic diseases that are still widespread throughout the world. Insects and domestic animals (cattle, sheep, swine, dogs, etc.) can transmit parasites to humans. While some parasites are specific to a region or a particular climate, others are found worldwide. Parasites infest their hosts to varying degrees in a variety of ways such as:
1. They rob the host of its nutrients;
2. They eat, digest, and destroy the host’s tissues;
3. They poison the host with toxic metabolic products.
Control of these parasites is now becoming a serious concern, due to the widespread and rapid development of resistance to chemotherapy. International Livestock Research Institute (ILRI), concluded that parasitism had the highest global index as an animal health constraint to the poor keepers of livestock throughout the world.
The major species of nematode parasites that cause major problems are Haemonchus, Ostertagia/ Teladorsagia, Tricho- strongylus, Nematodirus and Cooperia spp. However, nematode infections in grazing livestock are almost always a mixture of species.
All have deleterious effects and collectively they lead to chronic ill thrift. Economic evaluations consistently show that the major losses due to parasites are on animal production, rather than on mortality. Conventional methods of controlling nematode parasites of grazing livestock have been with the use of synthetic chemotherapeutic drugs.
Largely because of the remarkable developments in these products in terms of efficacy, safety, the spectrum of activity and remaining relatively inexpensive, livestock producers have relied almost exclusively on their use.
However, the spectre of resistance to all the major groups of broad-spectrum anthelmintic now looms large in the control of nematode parasites, particularly for the small ruminant industry, throughout the world.
(To be contd)