For many years ticks have taken a toll of exotic cattle (Bos taurus) introduced to tropical and subtropical developing countries. The most obvious effect of ticks has been as vectors of disease. The four conditions most responsible for loss are theileriosis, babesiosis, anaplasmosis and heartwater (Cowdria ruminantium) infection. A number of tick genera including Boophilus, Amblyomma and Hyalomma have pathological effects independent of their roles as vectors. The problem has been considered and some efforts at control made in North Africa (Sergent et al., 1945). Taiwan Province of China (Otte and Kiltz, 1968), Trinidad (Williams and Gonzalez, 1968), West Malaysia (Rajamanickam, 1970), Sri Lanka (Ranatunga and Wanduragala, 1972), India (Menon, 1974) and Bolivia (McCosker, 1975).
In recent years, interest in crossbreeding and demand for exotic cattle in developing countries have increased. In catering for this demand, some international and national bodies have underestimated the risks associated with the presence of pathogenic ticks in countries utilizing exotic cattle. This article is an analysis of causes of the currently high wastage of exotic cattle during and after importation to some countries, and also contains recommendations for reducing the loss. Although much of its content is based on experience with cattle exported from Australia, the same problems undoubtedly exist in other regions.
The author is with the Department of Primary Industries, Animal Research Institute, Yeerongpilly, Queensland 4105, Australia.
Choice of cattle
Exotic cattle are not always productive or healthy in the tropics because of poor adaptation to climate as well as to ticks and tick-borne diseases. Despite this, there is still a relatively uncontrolled flow of purebred animals from cool or even cold areas to equatorial and sub-equatorial regions. There are records of entire shipments of cattle dying, many shortly after importation, from disease and environmental stress. Attempts to introduce exotic blood in other ways are sometimes thwarted. Whereas artificial breeding is an admirable way of upgrading for production, the use of semen from a breed highly susceptible to an enzootic tick disease for which there is no vaccine or drug can have an undesirable effect. For example, Bos taurus × Sahiwal calves have died from theileriosis in Asia under circumstances in which a purebred Sahiwal might have survived.
Reasons for losses owing to breed unsuitability have to be defined. If climate is a limiting factor, there is no point in persisting with an exotic breed unless conditions are suitable for developing useful hybrid cattle. If climate is not a limiting factor, but tick diseases are a major hazard, these must be defined, and a decision made as to whether they can be controlled or not.
Production in a favourable environment still seems to be a major criterion for selection, despite the fact that a much more rigorous life awaits the animal in the tropics. Cattle selected in this way often fail to meet expectations. For example, the production of the champion cow of Tasmania (latitude 43°S) was reported to have fallen from “15 bottles a day to one bottle a day” on being exported to the tropics. A less impressive performer selected over several generations in subtropical, northern Australia (2 000–3 000 km closer to the equator than Tasmania and enzootic for Boophilus, babesiosis and anaplasmosis) may well have been a better choice.
This 2-year-old heifer is the result of intelligently applied crossbreeding in a developing country.
Often pregnant females are chosen for importation, presumably to increase cattle numbers as rapidly as possible. This can have the opposite effect, as was illustrated recently when, following the export from Australia of 1 000 cows in advanced pregnancy, 400 died within weeks of reaching their destination after experiencing severe stress. A recent project to import reared Sahiwal cross calves about six months old into a second country should produce good results over a longer period of time.
Some countries have been importing poor-quality cattle. Cheap purchases are sometimes made of cattle culled for various reasons in their country of origin.
Losses inevitably occur among such cattle, and they provide a poor basis for any programme of livestock improvement.
Organization and preparation
Many groups and individuals play a role before contracts for supplying cattle to a developing country are fulfilled. They include major lending institutions based in developed countries, government departments in the importing country, and selling agents and the veterinary department of the exporting country. After the contract is determined, field veterinarians and finally the private suppliers of the cattle in the exporting country become involved.
With this cumbersome system, liaison is often poor, misunderstandings occur, and the operation suffers accordingly.
Problems in the exporting country.
Some of the difficulties in the exporting country derive from insufficient time being allowed to fulfil contracts. The time available may be as little as four to six weeks, during which cattle are selected, sampled for health tests, tuberculin-tested, vaccinated, injected with antibiotic and sometimes moved from place to place before finally being gathered at a convenient holding-area prior to shipping. Even before the cattle are exported, they may suffer nutritional or other types of stress; and the mixing and crowding of a number of small groups while a consignment is being made up facilitate the spread of disease. There is seldom enough time to immunize susceptible cattle effectively against babesiosis and anaplasmosis, and sometimes vaccination is not performed at all.
A reason for the excessive activity and the short time available has been the existence of unrealistic health specifications. Cattle exported from Australia have had to be tested for contagious bovine pleuropneumonia, a disease that was eradicated there many years ago. Rigorous testing for diseases that almost certainly have a higher incidence in the importing country than in the exporting country - such as brucellosis - is usually performed. One health requirement for a group of cattle leaving Australia several years ago was that they be free of babesiosis and anaplasmosis, despite the fact that their destination was hyperenzootic for these conditions. When high dosages of a sterilizing drug were given to these stressed, pregnant animals, 20 percent of the group died before leaving Australia. Reasonable liaison has since been established with the country concerned so that cattle to be imported are now vaccinated instead of given sterilizing drugs.
At the other extreme, too little regulation has been applied in certain regions, with cattle being allowed to cross borders, sometimes illegally and without health checks, spreading disease and in one known instance even introducing acaricide-resistant ticks to a country previously free of this pernicious problem.
Problems in the importing country.
The factors governing the fate of cattle after export are complex. Obviously, the challenge they receive on arrival from Theileria, Babesia, Anaplasma, Cowdria or ticks per se, and the levels of pre-existing immunity the cattle possess against these parasites will have a major effect, even if in other respects the cattle are suitable for the new environment. Let us look now at the organizational deficiencies leading to stress and exacerbation of tick diseases.
Poor timing. Most countries import cattle randomly throughout the year so that animals physiologically adapted to winter are frequently shipped to the northern hemisphere during that region's summer. Thus, cattle with long coats can leave Australia and be exposed within hours, if the shipment is by air, to very hot, humid conditions. Countries in the northern hemisphere should avoid importing cattle from Australia during the southern late autumn, winter and early spring and consider alternative sources in the northern hemisphere if cattle are urgently needed during this period. The same considerations, although covering a different period, apply to developing countries in the southern hemisphere that import cattle from North America and Europe.
Bad conditions on arrival. Some consignments of cattle are known to have encountered very adverse conditions on arrival in the importing country. These include inexpert handling while being unloaded, inadequate nutrition and the immediate strong challenge of one or more tick diseases while the cattle are still stressed from their journey. Good unloading facilities, and quarantine areas (e.g., sheds or open, well-grassed fields with shade shelters) that are kept tick free and large enough to accommodate importations should be available for the cattle on arrival. Cattle unfortunately sometimes contract babesiosis from ticks carried to them on cut pasture.
Imported Hereford-zebu cross. Such animals require regular acaricidal treatment to control Boophilus microplus.
Lack of experience. Imported cattle suffer because of a lack of experienced personnel in developing countries. Inexperience leads to incorrect selection of cattle, the design of inappropriate health specifications, poor husbandry practices and ineffective disease investigation. In the last instance, there have been reports of losses due to babesiosis in cattle exported from Australia that cannot be rationally explained. An “outbreak” of babesiosis was stated to have occurred on a Boophilus-free island, and on another occasion in resistant Brahman-cross cattle originating in a hyperenzootic area of Australia and vaccinated before being exported. Small numbers of babesias or anaplasms are sometimes found in blood films taken from sick animals, even though babesiosis or anaplasmosis is not the primary cause of the disease. Misinterpretation of such findings in immunized cattle sometimes leads officials in developing countries to doubt the value of vaccination, jeopardizing the use of this worthwhile procedure.
Even when there has been good clinical evidence of tick-borne disease following importation of cattle, laboratory identification of the causative organism has on occasion been difficult to obtain owing to the lack of experience of personnel.
Prospects of controlling tick diseases
In considering control, diseases can be divided into three broad categories: those controllable by established immunological methods, providing these can be applied; those potentially controllable as a result of recent research; and those that are difficult to control in the tropics by chemicals or vaccines, but which, in certain cases, can be reduced in severity or avoided completely by management strategies. Before this discussion is developed it is necessary to reiterate the importance of defining which tick diseases are causing loss in a particular environment. This must precede any rational approach to control (Uilenberg, 1976).
Boophilus microplus infestations, such as this one, killed 23 of 79 imported Hereford cows in a developing country.
Controllable diseases. These include babesiosis and anaplasmosis. The principles of immunization have been known for 80 years, and efficient methods of vaccination were developed during the 1960s and 1970s (Callow, 1976). Effective drugs for treatment are also now available. The problems that remain are related to planning and organization. Appropriate vaccines, are available or can be prepared for susceptible cattle, even in a developing country (McCosker, 1975), but their effectiveness depends on how they are used. Immunization against an expected, strong challenge takes up to three months, and should be performed in the exporting country if possible. The procedures can be carried out in a quarantine area in the importing country, but problems of supplying and using vaccine and the risk that tick quarantine will break down make the first alternative preferable. The period required for immunization may be reduced if cattle are selected from areas enzootic for babesiosis and anaplasmosis, in which case they are likely to be at least partially immune.
Potentially controllable diseases.
Theileriosis due to Theileria annulata and T. parva has always presented a formidable barrier to the successful importation of exotic cattle into parts of Asia and Africa, although blood vaccines were useful against T. annulata in North Africa and the Near East (Pipano, 1974), and vector control with acaricides protects some cattle against T. parva. Recently, cultured T. annulata has been successfully used for vaccination (Hashemi-Fesharki and Shad-Del, 1973; Pipano, 1974), and research into alternative methods of immunization is encouraging (Gill et al., 1977). At the same time much progress has been made toward producing a vaccine against T. parva (Cunningham, 1977), which should eventually become available. Unfortunately, until vaccination against theileriosis is well established, exotic cattle being introduced to enzootic areas will continue to die in large numbers.
Diseases that are difficult to control. Disease caused by ticks per se, often underestimated in developing countries, is the least likely to be controllable by chemical or immunological means in the future. The effectiveness of acaricides can be expected to decline as ticks become tolerant to chemicals, and in some countries the increasingly high cost of dips and sprays will militate against their continued use. Biological control using tick-resistant cattle, especially Bos indicus breeds, should eventually succeed (Wharton, 1976), but the prospect is long-term, particularly for dairy cattle, and will depend on continuing endeavour by workers in animal production, breeding and parasitology in both developed and developing countries. In hot, humid regions some crossbred cattle with as high as 50 percent Bos indicus infusion suffer from heavy B. microplus infestations if not dipped regularly, and obviously these should be culled. Acaricide resistance in ticks, brought about by over-use of chemicals, has appeared in certain developing countries. The future for exotic cattle and a proportion of the crossbred animals dependent on chemical control appears bleak in such countries.
The possibility of eradicating ticks or holding populations at very low levels with minimal use of acaricides should be considered, although in developed countries eradication is usually rejected for economic and social reasons (Cattle Tick Control Commission, 1975). When acaricide resistance develops in a population of susceptible cattle in a tropical environment, this approach might have to be used as a last resort. Various forms of zero grazing, fairly common in some developing countries, lend themselves to the control of more than one tick species. The opportunity for keeping currently uninfested environments tick-free still exists in some countries where remote areas of virgin jungle are being cleared for cattleraising. B. microplus was kept out of at least two ranches in one south-east Asian country by ensuring that foundation stock were not tick-infested and by subsequently applying appropriate quarantine measures.
A laboratory technician records rectal temperatures of cattle being immunized against babesiosis in Santa Cruz, Bolivia.
Finally, the deleterious effects of B. microplus on cattle imported to areas favourable to this parasite may be reduced. First, if cattle have already been exposed to ticks in the country of origin they will have developed some acquired immunity, and will be less susceptible than those encountering B. microplus for the first time. There is thus a case for preferring cattle from areas enzootic for B. microplus, and also for subjecting cattle from other areas to controlled exposure to ticks before they are exported. Second, because the capacity to develop tick resistance is inherited and can be measured (Wharton, 1976), cattle could be selected for either individual or breed capability of resisting ticks. For example, Jersey cattle attain acquired resistance levels of nearly 98 percent against 85 percent for Holstein-Friesians (Utech, Wharton and Kerr, 1978), so that there is a good reason for recommending Jerseys ahead of Friesians in areas favourable for B. microplus. Third, it has recently been shown (Callow and Stewart, 1978) that active babesial infection coinciding with the first infestation of an animal with ticks interferes with the development of acquired immunity to ticks. This observation suggests that cattle experiencing tick, babesial and anaplasmal challenges immediately after arriving in a tropical environment should be effectively vaccinated beforehand to minimize parasitaemia at the initial challenge.
Turning to heartwater disease, although immunization against this condition can be performed, the procedures are relatively difficult to perform safely and conveniently (Uilenberg, 1977). Only limited advances in the study of heartwater have been made over the last twenty years, probably because of a relative lack of interest in the condition. There is a growing awareness of the significance of heartwater in attempts at livestock improvement in Africa (Illemobade and Leeflang, 1977), and an increased tempo of research can be expected. The difficulties of dealing with heartwater, outlined by Uilenberg (1977) are, however, considerable, and no forecast of the rate of progress toward practical control can be made.
Those bodies primarily concerned with livestock improvement in developing countries - the lending institutions, bilateral and international aid agencies and the governments of the developing countries concerned - should continue to ask basic questions about programmes for cattle improvement. For example, why are they necessary, are there other priorities, and what is the cost-benefit relationship of establishing cattle industries in a particular country? Progress and achievements should be closely monitored and reviewed regularly.
Information, training and education.
Influential and responsible bodies supporting and servicing the introduction of exotic cattle to difficult environments should become better informed of the complex problems associated with these enterprises. This applies mainly to the lending agencies and the relevant government departments in developing countries. Aid agencies might play a greater role than at present in providing information in the form of reports and manuals and in promoting active discussion and consultation between appropriate groups.
The lack of trained and committed people working in the animal industry in developing countries is relevant in the present context. The need is particularly great at two levels - field and laboratory investigation, and the management of cattle on farms. More postgraduate training, schools, workshops, training courses and practical experience on farms in developed countries than presently available would be of great benefit.
Research. More knowledge of the epidemiology of tick diseases, as a basis for rational control, is needed in all tropical environments. If the knowledge and experience to conduct the necessary investigations cannot be immediately provided by a country utilizing exotic cattle, the formation of international task forces trained to undertake this specialized work might be necessary.
Other worthwhile areas for more investigation are in the control of diseases caused by Theileria, the control of heartwater and in animal breeding. Progress made by groups in Israel, East Africa and recently in India opens up exciting possibilities for the control of theileriosis. If possible, extra financial support should be found for existing groups, and similar studies stimulated in other centres in the Near East and southern Asia. The impact of heartwater in Africa should be more closely examined, and, if the seriousness of this condition is confirmed, research into better means of control encouraged. Existing animal-breeding units, particularly in developing countries, should also receive more support in their work to improve productive potential and disease-resistance of indigenous and exotic cattle and their hybrids. Developed countries with tropical environments, such as Australia, could play a greater role in the development of cattle suitable for similar environments in developing countries.
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