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Dose only the animals in the flock/herd that appear to be clinically affected. These animals will be acting as a source of infection for the rest of the group. Follow the guidelines for anthelmintic use. Early diagnosis of clinical signs and good farmer awareness are required for successful use of this strategy.
This strategy is based on two principles:
1 In some farms, subclinical production losses are unavoidable and/or not significant to the farmers income perception. In these cases, the cost of routine drug treatment may outweigh the benefits that the farmer will achieve from their use. It is therefore better for the farmer to invest in treating only the animals which will benefit most from treatment. (It may also be found that particular animals are requiring treatment more often, in which case it may be more economical to slaughter these individuals).2 Where long periods of the year offer good conditions for larval development, treating the whole flock/herd whenever a few clinical cases appear will lead to the rapid development of anthelmintic resistance. Treating only the clinical cases reduces the proportion of the worm population that is exposed to drug selection pressure, slows the development of resistance and ensures that effective drugs are available for the future.
Clinical treatment against fluke may be effective in chronic conditions, however acute fluke can be caused by infection with large numbers of young flukes. Most of the readily available flukicides on the market will not be effective against immature flukes and may not have the desired effect when used on acute cases. Triclabendazole should be used in such circumstances.
Diagnosis of fluke and Haemonchus infection in sheep and goats is aided by proper identification of signs of anaemia. Observing the eye as described in the diagram, and comparing the colour with the eye card will help identify the animals in a flock that will benefit from treatment.
Figure
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KARI/DFID ANAEMIA CARD For more information refer to the KARI/DFID Manual of Integrated Helminth Control. This card is designed to help in the diagnosis of liver fluke and haemonchosis in sheep. In certain areas other diseases may cause anaemia. 1. Open the eyelid by pushing gently down on the upper eyelid with one thumb while the other thumb gently pulls the lower eyelid downwards. Produced by the KARI/DFID NARP II Project, c/o KARI, Box 57811, Nairobi, Kenya. |
Since levels of worm infection are related to the climate and seasons, it is possible to treat animals at particular times of the year or in response to weather patterns. Three main strategies are possible:
1 Treatment at times of peak infection
The purpose here is to treat all animals in the flock/herd at the time of year when it can be predicted that infection levels will be at their highest or just before this when animals are under their greatest challenge. Greatest challenge is usually a few weeks after the onset of the rains.
While there are drawbacks to such a strategy in areas or seasons where there is prolonged rain, this scheme might be particularly suitable in more arid regions where rains are brief and larvae on pasture do not survive long after the rains stop.
Such a treatment may prevent the onset of clinical signs but may not prevent production losses or the build up of pasture infection levels for later seasons.
TREATMENT AT TIMES OF PEAK
INFECTIONS
In practice, peak infection levels will commonly occur about 4-6 weeks after the onset of the rains and hence treatments at about 3-4 weeks into the rains may prove effective. If the rains prove to be prolonged or where grazing is a shared resource, a second treatment may be required 4-6 weeks later. The use of rafoxanide or closantel at this time in areas where combined fluke and Haemonchus infections are common may prove beneficial.
2 Treatment to alleviate chronic Infections
Infection with low numbers of Haemonchus at times of poor nutrition can lead to a chronic syndrome which can be difficult to diagnose. Animals respond well to an improvement in nutrition and/or treatment with an anthelmintic.
TREATMENT TO ALLEVIATE CHRONIC
INFECTIONS
Usually such a treatment is likely to be most beneficial during the long dry season or in periods of drought. The earlier in the dry season that treatments are provided the less that body condition will have deteriorated and the greater the animal's chance of surviving through to the next rains. Treatment should not be before the pasture has started to brown off or else the animals may become reinfected after treatment.
3 Treatment against inhibited worms
Haemonchus larvae can enter a period of arrested development within the host in order to delay adulthood and egg laying until conditions are more suitable for transmission. There are two likely stimuli for this delay in development: the onset of host immunity and exposure of the infective larvae to increasingly arid conditions on pasture. In the first case, larvae will not develop further until there is a relaxation in immunity such as may occur during periods of nutritional stress, intercurrent infection or in late pregnancy. In the latter case, the stimuli for the larvae to recommence development are unknown but it is thought that this may occur randomly through the dry season, ensuring that the host always has a low but egg-producing worm burden.
TREATMENT AGAINST INHIBITED
WORMS
The purpose of treating animals to eliminate the burden of inhibited larvae that they are carrying is to prevent them recontaminating pasture when conditions become more suitable for larval development. Thus female sheep or goats, treated in mid pregnancy may have a lower egg count through lambing and contribute less to infecting their offspring. Also by treating animals in the arid lands in the middle of the dry season, there should be fewer worms to contaminate grazing during the rains.
In areas of high temperature and humidity, helminth eggs hatch very quickly and can develop into infective larvae in a short period, however they also expend their energy reserves quickly and cannot survive as long on pasture as they might in cooler or drier areas. This feature can be exploited by moving animals round a number of grazing areas ensuring that they have left an area before the eggs have developed into infective larvae and that the animals do not return to that area until all the larvae have died.
In practice it is best for animals to be moved every three and a half days, say Monday morning and Thursday lunch-time. They are rotated round eight to ten areas before they return to the original area.
It is very important that the rotation discipline is maintained since the whole system relies on animals not returning to any area before the month is finished. Also animals must move as planned or they will begin to be infected if they spend any longer on the initial area.
This system lends itself to places where the grazing area is controlled by one livestock owner and is particularly suitable for use in tethered grazing systems. It is unlikely to prove practical in communal grazing systems.
The principle of this system is to always move "clean" animals onto "clean" ground;
DOSE AND MOVE PROCEDURE
Animals are treated with an effective anthelmintic and moved onto grazing that has not been used by livestock for a suitable period. (The length of time that the area should have been free of stock will vary from area to area, perhaps six weeks at the coast to six months in the Highland areas).
Medicated feed blocks are high energy feed and mineral supplement blocks incorporating an anthelmintic. Animals can have access to these blocks at night in the boma and effectively worm themselves. The continued ingestion of low levels of anthelmintic can help to overcome anthelmintic resistance and the additional mineral, protein and energy supplement can be very beneficial to animals during times of nutritional stress. Problems may be encountered with particular animals that do not take to the blocks, but in most cases animals will learn very quickly by watching others. Blocks are not currently commercially available in Kenya, however the technology required to make them and the ingredients are all readily available:
2 volumes molasses
1 volume urea (fertiliser grade)
1 volume cement
½ volume common salt
½ volume mineral premix
2 volumes maize germ (or other suitable bulking product)
1 × 100 kg cow dose of a benzimidazole anthelmintic per kg of ingredients
1 volume water
The technique is essentially that of making concrete blocks. Thoroughly mix half the water with the urea until the urea granules dissolve. Mix in the anthelmintic then the cement and most of the remaining water. Add the molasses, the salt and mineral premix and the remaining water. Finally add the maize germ or other bulking agent. It is important that the ingredients are mixed well before the addition of each additional ingredient. After all the ingredients are well mixed, pour the mix into moulds (buckets, basins, pots or wooden frames). Stand the moulds in the sun for 3-4 hours then turn the blocks out of the moulds and allow them to dry for a further week before use.
Blocks should be placed in the boma protected from rainfall.
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Caution: If animals (especially sheep) consume too much of the block at once they can suffer from urea poisoning. It is important that blocks are introduced gradually and that the consistency is not too soft otherwise an animal may eat too much. Since ingredient quality can vary greatly the above recipe can only act as a rough guideline. |
Where toxocarosis is a problem in young calves, calves should be treated with piperazine at 6 weeks of age.
When haemonchosis is present or a chronic condition of haemonchosis and fasciolosis, animals can be treated with a salicylanilide drug such as rafoxanide or closantel. These drugs have the added benefit of treating the animals for nasal bots.
Use of a narrow spectrum drug rather than a combined fluke and worm drench helps reduce the usage of the broad spectrum wormers and slow the onset of anthelmintic resistance.
By using a "leader and follower" system, the cleanest pasture can be retained for the more susceptible animals and the more contaminated pasture can be grazed by the most resistant stock. These latter animals may also help clean the pasture of infectious larvae.
The "leaders" in the system are normally the younger animals and the followers the older animals. The system can also utilise differences in breed or species susceptibility, with small ruminants grazing ahead of cattle or more resistant genotypes such as red maasai sheep grazing behind more susceptible types.
Bomas often become sources of infection with high numbers of infectious larvae in the surrounding herbage and in the pasture immediately adjacent to the boma. The frequent movement of bomas can reduce the rate of reinfection from such areas. Normally bomas should not return to the original position within one year. The more often bomas can be moved the better. Such a practice can also lead to a reduction in cases of pneumonias. While the use of more mobile (and hence less robust) bomas may lead to an increase in the numbers of animals lost to predators, the benefits in terms of animal health can often overcome any such losses.
It has been shown that some breeds of animal are less susceptible to worms than others. Thus indigenous fat-tailed sheep are often more resistant than exotic types. Where losses to helminths are difficult (or expensive) to control, the use of these animals can minimise the need for other control strategies. Using indigenous fat-tailed rams for crossing into an existing flock can produce not only an improved resistance to worms but also introduce the benefits of hybrid vigour and increased hardiness to other conditions.
In order to minimise dependence on the broad spectrum wormers, the use of salicylanilide products at particular times of year can eliminate fluke and Haemonchus burdens and (in the case of closantel) provide a period of protection against reinfection. At other times of year a normal broad spectrum drug should be used to prevent a build up of other worm species such as Oesophagostomum.
In practice, salicylanilides are perhaps best used at the start of the rains with a broad spectrum drug used at other times.
Rafoxanide (Ranide or Ranox) and Closantel (Flukiver) can be difficult to obtain in Kenya but can be more frequently found in combination (rafoxanide with levamisole as Flukazole or Multidose).
The rotation of cropping areas and grazing areas can be used to prevent pasture larval burdens becoming excessive.
The purpose of seasonal treatments against fluke is twofold: firstly to remove burdens of flukes in the livestock and secondly to reduce the contamination rate amongst snails.
Treatments should therefore be at times of peak infection and during periods when snails are not active (during droughts or floods).
FAO guidelines suggest that for the Kenya Highlands, treatments should be in February, June and October.
Seasonal treatment is unlikely to be successful in preventing infection unless both the grazing and the watercourse are under the farmer's control or if all the farmers sharing these resources act together.
NOTES
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Produced By:
KARI/DFID NARP II Project
c/o KARI, Box 57811, Nairobi, KenyaCompiled by RK Bain
Designed by The Mediae Trust and Development Communications 1999
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