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This article was published in 1964
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.

Internal Parasites of Cattle in New South Wales

L K. HOTSON, B.V.Sc., Veterinary Research Station, Glenfield, N.S.W.

INTRODUCTION

Helminthosis is receiving increasing recognition as a specific disease problem and a cause of economic loss to the cattle industry. Accurate diagnosis of the disease, and the planning of effective control measures, are important functions of the Veterinary Inspector. This paper provides some general information on the distribution of important parasites in N.S.W., the diagnosis of helminthosis, and the epidemiology and control of the disease in cattle.

DISTRIBUTION OF PARASITES.

Information regarding the incidence of helminthosis in cattle in Australia is meagre, Roberts et al. (1952), and Rick et al. (1953) have reported on the epidemiology of parasitic gastro-enteritis in cattle in south-eastern Queensland, and Roberts (1957) has recorded the incidence of calf parasites at Tooradin in Victoria. Peterson (1957) recorded the seasonal occurrence of various parasites in Western Australia.

Extensive survey work to study the epidemiology of helminthosis in cattle in N.S.W. is planned to commence this year, and C.S.I.R.O. workers will be initiating similar studies in southern states. Information obtained from these observations will be of particular value in the planning of control measures against helminthosis in these areas.

Helminthosis is mainly seen in younger cattle, being common in dairy calves from 3-9 months of age and in beef weaners, although stock of any age may be affected. The disease commonly occurs in areas of higher rainfall on the coast and tablelands, but under certain conditions it may become a problem in drier areas of the State. Losses commonly occur in winter and spring, but may occur at any time of the year, the incidence being closely related to the current rainfall pattern.

The northern half of N.S.W. is an area of predominantly summer rainfall, and within this area the most important parasite species are Haemonchus placei, Bunostomum phlebotomum, Cooperia punctata, C. pectinata and Oesophagostomum radiatum.

In the southern half of the State, where winter rainfall predominates, the important parasites are Ostertagia ostertagi, Trichostrongylus spp., Nematodirus spp., Cooperia spp., Oesophagostomum venulosum and Dictyocaulus viviparus.

There is considerable overlapping of the two areas, and in the broad intermediate region of the State where rainfall has no marked seasonal incidence, any of the above parasites may occur at favourable seasons of the year.

Of the common trematode parasites of cattle, Fasciola hepatica occurs in coastal and tableland areas, and also in inland irrigation areas, while various Paramphistome species have a mainly coastal distribution, bu particularly prevalent on the North Coast.

DIAGNOSIS OF HELMINTHOSIS.

Diagnosis of parasitism in cattle requires consideration of several factors, since commonly observed symptoms of diarrhoea, loss of condition and anaemia may have a variety of causes, and may not necessarily be due to internal parasites. Knowledge of the age of affected animals, and of the usual seasonal incidence of helminthosis in an area, coupled with consideration of current seasonal conditions, nutritional status of animals and management practices on the property, will assist in making a diagnosis. These factors must all be considered when assessing the significance of egg counts and worm counts.

Faecal egg counts and larval differentiation are of value in determining the type and severity of infections where counts are appreciable, but such counts give no indication of the presence of immature worms, or of adults in which egg-laying has been affected by immune reactions of the host. Therefore, negative egg counts do not indicate necessarily that parasites are absent.

Because interpretation of faecal egg counts depends on consideration of many factors, it is essential that field officers should include a full history with specimens submitted to the laboratory. The assistance, which the laboratory diagnostic officer can render to field officers, will be much more effective if samples submitted to him are properly collected, adequately labelled, and accompanied by information relative to the age or body weight of animals sampled, type of pasture, stocking rates, management practices, and relevant rainfall. Where a herd problem is under investigation, submission of a number of identified samples is desirable so that an accurate estimate of the level of herd infection may be made.

Diagnosis by worm counts may or may not prove to be conclusive. Cattle which have had severe diarrhoea, or which are moribund, may have passed most of their worms in the faeces, leaving very few for a post-mortem count. Examination of samples from such animals may be misleading. Interpretation of worm counts depends on the species present, their abundance, and the age and condition of the affected animal. Since the immature stages of several species can have severe pathogenic effects, examination of the abomasal and small intestinal mucosa, for these stages, is also an important part of diagnostic procedure.

EPIDEMIOLOGY OF HELMINTHOSIS IN CATTLE.

Two main factors dictate the extent of the worm burden developing in grazing cattle at any given time. These are, firstly, the "infectivity" of pasture, or the availability of infective larvae to cattle, and secondly, the immune status of the host.

1. Availability of larvae.

It has been shown that there is sufficient moisture present in the cattle dung pat to permit the hatching of eggs and the development of larvae to the infective stage. Steady soaking rain, which wets the pat thoroughly, is essential, however, for the escape of these infective larvae to the pasture. Not all larvae are released from a pat at one time, and Durie (1961) showed that Summer pats could remain a reservoir of larvae for five months under Queensland conditions and that Winter pats did so for up to eight months. The continued contamination of pastures with larvae from infected dung pats, even in the absence of cattle, is a complication in planning parasite control by pasture management.

Larvae of most of the common strongyloid parasites become available to grazing animals by migrating to pasture from the dung pat. However, Bunostomum larvae do not migrate, but infect the host by skin penetration. For this reason, conditions in muddy calf yards and in swampy paddocks are ideal for these larvae to gain access to new hosts.

Environmental temperatures dictate which species will develop within the dung pat, but rainfall is necessary for larvae to become available to grazing animals. Infections in Summer rainfall areas are normally picked up in the wet Summer and early Autumn, and these infections exert their greatest effects on the host during Winter months when the nutritional level of pasture is generally low. In Winter rainfall areas infection is acquired from late Summer onwards, and burdens increase during Autumn, Winter and Spring.

2. Immune status of the host.

The extent to which ingested larvae will develop is governed by the host's immune status. Young calves introduced to a contaminated environment are highly susceptible, and heavy worm burdens will develop if larvae are available. However, once cattle have experienced infection with most of the common nematode parasites, a fairly firm resistance to reinfection develops. For example, immunity to Bunostomum, Cooperia and Nematodirus appears to be quite strong, and develops early in life. Immunity to Haemonchus may not be stable until animals are 18 months of age, and immunity to Ostertagia and Trichostrongylus may not be strong until animals are much older. There appears to be little immunity developed to Fasciola, as this parasite may be present in large numbers of cattle of any age.

The constant stimulus of worm infection is necessary for the maintenance of immunity. During dry periods when few infective larvae are available to grazing animals, there is little stimulus for the development or maintenance of host immunity, and cattle may be in a highly susceptible state when suitable rainfall releases larvae from contaminated dung pats.

A degree of immunity developed to a certain level of pasture infection may break down when this level is exceeded. This may occur after rain, or when pasture deteriorates and cattle graze closer to dung pats or overcrowd choice areas of pasture.

Good nutrition enables cattle to tolerate the effects of parasitic infection, rather than to resist the establishment of such infections. There may be an apparent breakdown of host immunity when a fall in nutrition permits established parasites to exert greater pathogenic effects on the host. This can occur without the acquisition of further infection.

Increasing worm burdens are therefore likely to be encountered when there is increased availability of larvae due to climatic or management factors, and when host immunity either has not developed or is at a low level.

CONTROL OF HELMINTHOSIS.

Control of helminthosis in cattle implies the suppression of parasite burdens below that level at which economic loss may occur. Judicious pasture and animal management plays a substantial part in control, but under conditions where management techniques are inadequate, anthelmintics must be used to limit worm populations.

Management should be concerned particularly with provision of a high level of nutrition for all stock, with particular attention to the needs of young animals in the immediate post-weaning period. Avoiding the use of a permanent weaner paddock on beef properties, and elimination of the permanent calf pen seen on dairy farms, will avoid the high larval contamination usually associated with such paddocks.

Care should be taken to recognise the dangers of overcrowding choice feed areas and grazing of swampy places in dry times. Contaminated pastures should be regularly spelled for as long a period as possible, or else should be grazed by adult stock known to have a strong degree of immunity. Treatment of snail habitats or the fencing-off of "danger areas", are important in trematode control.

Under extensive husbandry conditions such as those employed in certain beef-raising areas, control of parasites by animal and pasture management may be sufficient. However, intensive control measures are necessary in dairy herds and where animals are run on improved pastures at high stocking rates. Under these conditions control by the multiple small dose regime of anthelmintic administration (by lick or in milk) might be considered as a means of reducing the substantial contamination which occurs.

Where anthelmintics are necessary for parasite control they should always be administered according to a definite plan, based on epidemiological knowledge for the area concerned. In this way, outbreaks of parasitism can be prevented, and anthelmintics can be used economically and to best effect.

Thus in Summer rainfall areas of the State, two treatments in Summer, and further treatment in Autumn and Winter, may be necessary to keep worm burdens at low levels. In Winter rainfall areas, regular treatments in Spring and Autumn are advisable, and in areas of non-seasonal rainfall, treatments must be adapted to suit the local rainfall pattern.

Anthelmintic treatment of both dairy and beef stock at weaning is advisable. Other treatments will depend on management and climatic factors on individual properties. Supplementary treatments should be applied at times when infectivity of pastures increases, or when animals are more susceptible to the effects of infection due to a lowered plane of nutrition

If regular anthelmintic treatment of cattle is contemplated on a property, the provision of a good crush and strong yards will encourage effective application of such treatments. The increasing use of injection techniques emphasises the need for anthelmintic formulations which can be easily administered, particularly to adult beef cattle.

Choice of an anthelmintic depends usually on effectiveness, safety and price of the anthelmintics currently in use for nematode parasites, the organic phosphates show reasonable efficiency, and they are relatively cheap. They have the disadvantage of occasional unpredictable toxicity.

The generally safer anthelmintics of the pyridine and benzimidazole groups have the disadvantage of being more expensive than the organic phosphates, but they are generally more effective against a wider range of parasites.

Anthelmintics for trematode parasites of cattle are currently under going extensive investigation, particularly regarding the use of injectable formulations.

Full information on formulation, efficiencies and dose-rates of anthelmintics for cattle is given in a recent review article by Hotson (1963), and as an excellent reference for general information on all veterinary anthelmintics, including those for cattle, the monograph by Gibson (1962) is particularly recommended.

References:

Durie, P. H. (1961) — Aust. J. Agric. Res., 12: 1200
Gibson, T. E. (1962) — "Veterinary Anthelmintic Medication" Tech. Comm. No. 33, Commonwealth Bureau of Helminthology, 1st Edition
Hotson, I. K. (1963) — Aust. vet. J., 39: 108
Peterson, J. E. (1957) — Aust. vet. J., 33: 108
Riek, R. F., Roberts, F. H. S. and O'Sullivan, P. J. (1953) — Aust. vet. J., 29: 122
Roberts, F. H. S., O'Sullivan, P. J. and Riek, R. F. (1952) — Aust. J. Agric. Res., 3: 187
Roberts, F. H. S. (1957) — Aust. vet. J., 33: 174