Prevention and control of parasitism in livestock
- Part 1 -

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.

In a future where the very real possibility exists that resistance will have rendered all chemical families of anthelmintic ineffective, this is cause for serious concern and for escalation of efforts to develop sustainable helminths control technologies.

Owing to favourable climatic conditions for development and survival of are parasitic stages and in absence of alternative control strategies, control of parasitic gastroenteritis in ruminants is primarily attempted by the frequent use of anthelmintic at short intervals, particularly in intensive and semi-intensive management systems, which has been shown to result in the emergence of very high levels of anthelmintic resistance.

Efforts are now being made to develop and use control options alternatives to chemotherapy, viz., targeted selective treatment, grazing management, biological control, host resistance to parasites, worm vaccine etc., which would not only reduce the use of chemical anthelmintic but also the cost of animal production as a whole.

The control strategies alternative to chemotherapy reveals that some of them are in the technology stage while others are still under research and development. Biological control by predacious fungi, worm vaccine, and exploitation of breed resistance are still undergoing laboratory research while targeted selective treatment, grazing management and exploitation of nutrition-parasite interaction can immediately be applied as an adjunct to chemotherapy.

The requirement today is coordinated, continued and committed effort for technology transfer and extension education to achieve the goal of "sustainable Parasite Control".

For better livestock productivity, it is essential to free from diseases, selection of high producing animals and optimal feeding. Helminths infections are a major cause of production loss in all cattle-producing countries in the world. With the advent of the broad-spectrum anthelmintic, the more dramatic and obvious effects of clinical parasitism are seen less often in many countries.

However, the subclinical effects in cattle whose outward appearance disguises the adverse economic impact is still a problem of great magnitude. The goals of control are as follows:
a. Prevent heavy exposure in susceptible hosts
b. Reduce overall levels of pasture contamination,
c. Minimize the effects of parasite burdens
d. Encourage the development of immunity in the animals

Endoparasitic infection is probably one of the most economic and production losses in livestock worldwide. It decreases feed intake, utilization of feed, body weight gain, milk production and reproductive performance.

It is also important concerning the development of a resistant strain of gastrointestinal parasites to broad-spectrum anthelmintic. Pasture management combined with nutritional supplementation with concentrates and /or forage is the most anti-parasite strategy in organic livestock farming.

Grazing Management

Grazing management in worm control programmes based on epidemiological knowledge is simply to provide clean pasture on which stock may safely graze. There are various forms of grazing management usually practised to control worm burden in various places. Grazing management is one of the ways of reducing the frequency of anthelmintic treatment. Grazing management strategies may be of preventive, evasive or diluting.

1. Alternation of host species: Alternate or integrated grazing has been used to control gastrointestinal parasites in ruminants. It is common practice to graze calves followed by older cattle, taking advantage of increased resistance in these older immunocompetent animals. Small ruminants and cattle, small ruminants and horses, or horses and cattle are the most logical candidates for alternate grazing strategies.

A recent study of mixed (and alternate) grazing with nose-ringed sows and heifers, showed promising results in controlling Ostertagia infections in the cattle whereas the little effect on the nematode infections of sows was noted.

2. Rotational grazing: This is a grazing management technique involving the intensive subdivision of a pasture in which each constituent paddock is grazed for a short time and then spelt for a relatively much longer time.

In a simple example, the total area for grazing subdivided into 15 paddocks, each of which could be grazed for 1 week and spelt for 14 weeks. The grazing time in such a system is thus 1 week, and the rotation length is 15 weeks.

Ticks were eradicated from a costal island in Queensland by removing all known hosts for 5 months and larval survival was almost zero after about 16 weeks. One modelling study for B. micro plus in Australis indicated that a single annual spelling period in summer of between eight and 12 weeks would substantially reduce tick populations.

To be continued...