Previous Page Table of Contents Next Page


As stated previously, several factors and issues are deemed to have important bearing on the role trypanotolerant livestock play now and in the future. Among them are changes in the larger ecological settings, production systems (e.g. intensification of production), societal or market valuation of trypanotolerant stock, numbers of trypanotolerant stock and availability of scientific breakthroughs in disease control and improvements in the level of tolerance. In the section below, discussions about these factors and issues are presented to set the stage for the design of a framework for analysing the roles of trypanotolerant stock in tsetse-trypanosomiasis control.

Changes in ecological settings

With respect to cattle, the geographical distribution of trypanotolerant breeds is closely linked with changes occurring in the larger ecological settings as well as those occurring in the localized production systems or environments. These linkages arise from both the presence of non-trypanotolerant livestock that often share the same resources as tolerant stock and tsetse flies that use the same environments as habitats and for breeding grounds. The overwhelming larger numbers of trypanosusceptible Zebu and their continued preference by many farmers restrict trypanotolerant cattle to tsetse-infested areas. Long-term climatic changes, such as drought, that eliminate tsetse habitats and reduce the size of the tsetse belt permit the occupation of previously tsetse-infested areas by susceptible breeds, forcing the tolerant stock to move southwards. Similarly, farming practices, such as slash and burn, and other urbanization pressures, such as the rapid removal of trees for fuel wood, destroy tsetse habitats, often resulting in the migration of Zebu cattle into areas further south, putting pressure on the tolerant cattle. Long-term climatic changes in areas outside the domains of trypanotolerant stock also affect their distribution - for example, the movement of larger numbers of transhumant cattle southwards in periods of drought.

Opinions differ as to the extent to which recent changes in climatic patterns in West Africa, urbanization and farming practices have affected tsetse-transmitted trypanosomiasis. Human activities have different impacts on tsetse species - for example, the palpalis group show more resilience to human-induced disturbed environments (Jordan, 1988). Reviewing the factors that influence the production potential of trypanotolerant livestock, Ferguson (1988) classified such factors as “fixed” (those that tend to be static in the medium to long term) and “dynamic” (those subject to significant change over the short to medium term). For the fixed factors, such as climate and natural resource base, Ferguson cited von Kaufmann (1986) and Bourn, Milligan and Wint (1986) as having exposed the fallacy in the belief that expansion of crop production involves a decline in ruminant livestock production. Jordan (1979), Putt et al. (1980) and Bourn, Milligan and Wint (1986) all referred to the rapidly accelerating disappearance of the tsetse fly species Glossina morsitans in West Africa, especially in Nigeria, mainly owing to cultivation and tree removal, and predicted the extinction of this species.

Murray and Gray (1984), on the other hand, argued that, at the continental level, the net effect of agricultural expansion and tsetse control has been small and that the problem of trypanosomiasis was escalating and would continue to do so unless more active steps were taken to control the disease. MacLennan (1980) reported significant advances in the spread of tsetse in several countries including Nigeria and Cameroon. In 1987, a number of experts indicated that the trypanosomiasis situation was worsening in their countries (ISCTRC, 1987). For example, trypanosomiasis prevalence in Senegal was reported to have risen by 15 percent in the same year that the rains returned after several years of drought (Diate, 1987). However, the 1985-87 survey of trypanotolerant livestock (ILCA, 1992) supported the view that the distribution of the tsetse fly, which directly related to changes in the climate, had changed over time and suggested that the northern distribution limits, depending on the country, may have shifted between 50 and 100 km further south than observed in the 1977-78 survey. Ferguson (1988) concluded that tsetse population density and distribution are area and time specific and that generalizations at a regional level or even a national level could be misleading. This last statement could imply the need to be cautious in predicting the emergence of vast tsetse-free environments, which some believe would make the value of trypanotolerance less important.

The discussion presented in the preceding sections points to the need to monitor the trends in the habitat changes of trypanotolerant livestock and how these are affecting both their distribution and performance. Information from such an effort would be needed in determining the comparative economics and the continued justification for promoting these breeds. A first step in this direction is to describe and document these breeds at a particular period in time and their uses and productivity levels during this period, as baseline data, to which subsequent assessments could be compared. Rege, Aboagye and Tawah (1994) used existing information to establish such a baseline for Shorthorns.

Agro-ecological zones and production systems

Jahnke (1982) presented strong arguments for placing farming systems (including livestock production systems) in the context of ecological zones, because this approach has the advantage of providing information on the basic resource endowment (livestock-land and land-human ratios, the extent of tsetse infestation and the productivity of the land). Three large classes of production systems were identified by Jahnke (1982), namely range-livestock, crop-livestock and landless systems. Whereas crop-livestock and landless systems can be associated with all five major ecological zones (defined below), an important subclass of the range-livestock system, the pastoral system, tends to be concentrated in the arid zone (defined below).

Distribution of tsetse-infested areas by ecological zones in West Africa in relation to sub-Saharan Africa

Ecological zone

Size of area
(1 000 km2)

%in West Africa

Tsetse-infested area
(1 000 km2)

% infested in West Africa






4 050

1 442


2 036




4 858



3 298

1 016



4 137



3 741



Source: Derived from figures of Jahnke, 1982.

Based on the number of growing days (GD - defined as a day during which precipitation exceeds potential evapotranspiration), agro-ecozones were defined by Jahnke (1982) as: arid (fewer than 90 GD), semi-arid (90-179 GD), subhumid (180-269 GD) and humid (³270 GD). A fifth zone, the highlands, ranges from semi-arid to humid and was defined as lands where mean average daily temperature is less than 20 °C during the growing period.

The land surface area of tropical Africa is estimated to be 22 362 000 km2 of which 8 327 000, 4 050 000, 4 858 000, 4 137 000 and 990 000 km2 were of arid, semi-arid, subhumid, humid and highlands zones, respectively, in the 1970s. Approximately 48, 36, 24, 17 and 0.5 percent, respectively, of these zones were found in West Africa. In West Africa, the “tsetse belt” excludes the arid zone as tsetse flies are only found along riverbanks. If the highlands zone is similarly excluded because of its minute size, approximately 2 485 000 km2 (75 percent) of the 3 336 000 km2 comprising the semi-arid, subhumid and humid zones of West Africa were believed to be infested with tsetse (Jahnke, 1982). The respective percentages of the semi-arid (1 442 000 km2), subhumid (1 187 000 km2)and humid (707 000 km2)zones infested with tsetse were 51, 86 and 99 percent (Table 6). More recent information based on overlays of cattle density and tsetse-distribution data presented by Kristjanson et al. (1999) shows that approximately 42, 95 and 99 percent of the semi-arid, subhumid and humid zones of West Africa, respectively, are infested with tsetse. The infested areas of the ecozones contain approximately 38, 86 and 94 percent of all cattle in the respective zones (Table 7). Because only one large-scale tsetse control programme has been implemented in West Africa, in which 9 000 km2 were treated with insecticide in northern Nigeria, it can be argued that most of West Africa remains infested with tsetse. In a recent review, Agyemang (2000a) noted that, with the possible exception of Mauritania, all countries in West Africa are still infested with tsetse.

Number and density in tsetse-free and tsetse-infested areas of West Africa by agro-ecological zone

Ecological zone

Total cattle

Cattle in tsetse areas

% in tsetse- infested areas

Density in infested areas

Density in tsetse free areas































Source: Kristjanson et al., 1999, cited in FAO, 2000.

Livestock production systems in tsetse-affected areas in West Africa

Pastoral systems in arable areas

Pastoral livestock production is typically associated with arid zones but in West Africa there is a long-standing tradition whereby pastoral herds penetrate into the more humid areas (semi-arid, subhumid and humid) during seasons when fodder and water become scarce in the north. Pastoralists also tend to remain in these more southerly areas where the tsetse challenge allows this and/or where an acceptable degree of tolerance of the stock has developed (Jahnke, 1982). Recent surveys in West Africa have indicated more permanent settlement by these pastoralists near peri-urban areas to take advantage of market demand for livestock products, especially milk (Jabbar, 1993; Jabbar et al., 1998).

The pastoral herds are typically non-trypanotolerant, but with time some trypanotolerant livestock have been added to these herds, as observed in the Oyo area of southwest Nigeria (Agyemang et al., 2000; Jabbar, 1993). The more the attributes of the newly acquired trypanotolerant livestock are appreciated, the more they are incorporated into the herds. Whether the penetration into humid areas is seasonal or permanent, important complementary and competitive relationships develop between cropping agriculture and livestock production (Jahnke, 1982).

Crop-livestock systems

These are systems in which cropping and livestock husbandry are practised in association. The nature of association may be loose or close. The association depends on the agroclimatic conditions and population pressure. In West Africa, the crop-livestock area in the lowlands spans three ecological zones, from the semi-arid to the subhumid and the humid. Cropping systems vary from location to location, even within zones, depending on moisture availability. In general, placing ecological conditions and the cropping systems on one axis and human population pressure on the other can be used to form a grid of gradients to characterize the farming systems in the mixed farming areas (Jahnke, 1982).

An opposing factor that diminishes the extent to which crop-livestock systems can develop is tsetse-trypanosomiasis. In general, as tsetse challenge increases it becomes increasingly difficult to keep susceptible domestic stock because they succumb to trypanosomiasis. Trypanotolerant breeds of cattle, sheep and goats replace trypanosusceptible breeds where no previous investments in tsetse control or chemotherapy have been made. Human population pressures that lead to the clearing of expansive areas for settlement and cropping could lead to the establishment of intensive crop-livestock integration. With increasing demand for livestock products, the potential for the emergence of market-oriented production systems also increases. At least two scenarios can emerge. In the first scenario, trypanotolerant livestock can compete with susceptible livestock with respect to special functions (e.g. draught power or meat production) and thus become part of the major production systems, for example where N’Dama or Baoulé cattle provide draught power in farming systems in which cotton is a major cash crop. In the second scenario, trypanotolerant breeds may not be competitive themselves, for example, for milk production, but their crosses with susceptible breeds can result in breeds that are highly competitive for production and have some level of resistance to major diseases. The use of N’Damance (N’Dama x Abondance) in central Côte d’Ivoire and N’Dama x Friesian or N’Dama x Jersey in the derived savannah/humid zones of Ghana and in the coastal semi-arid areas in the Gambia can be cited as examples of crop-livestock systems evolving into market-oriented systems in response to a high demand for livestock products.

Trypanotolerant livestock in changing physical and market environments

As the number of trypanotolerant livestock expands through the normal utilization and breeding processes and through conservation efforts, uses other than for meat production, for example, draught power (in highly priced cash crop areas), milk production (in peri-urban areas), etc., are likely to develop in special niches. Both the physical environment and the market set-ups for these new production systems need to be characterized ex ante to ascertain their potential survivability and profitability. However, for such ex ante characterization of new or emerging systems to be reliable, it must draw on available information on special features in the present environments that are likely to change or be missing in the new environments, in order to forecast how these might affect the unique attributes exhibited by the animals. For example, if trypanotolerant cattle previously not developed for work were to be introduced for draught purposes into highly tsetse-infested areas, how would the interaction of work and increased disease risk affect trypanotolerance? Would trypanotolerant cattle have any economic edge over susceptible cattle for work in tsetse-free areas on account of resistance to other endemic diseases? These types of questions are suitable for ex ante economic and impact analyses.

Valuation of trypanotolerant livestock

There is a need to provide an economic rationale for trypanotolerant livestock that goes beyond their tolerance characteristics in view of the increasing population of the tsetse-infested areas by trypanosusceptible breeds and the increasing prospects of tsetse control in these areas (de Haan, 1988). De Haan (1988) considered that a comprehensive technical and economic evaluation to define optimal conditions for trypanotolerant livestock would be a first step in achieving a better use of the existing population. Improved utilization also implies that the production potential of the breeds is fully exploited. Thus, attention should not only be directed to meat production, but should include milk and draught power production (Tacher et al.,, 1988; McIntire, 1988). Field observations in the Gambia have shown that N’Dama cattle are often used for traction within their areas of distribution (Republic of the Gambia, 2002) and even the females of the breed are sometimes used successfully, an observation further confirmed in Senegal by Lhoste (1986). The contribution of N’Dama milk for human consumption in special niches has already been established (Agyemang et al., 1991b; 1997). The inclusion of this diversified production would not only increase the value of these stocks to the national economy as measured by GDP and hence attract attention and support for their development and conservation, but would probably also influence their sale value, including export. As referred to in chapter 2, initial results from economic evaluations of various livestock systems suggest that there is an economic rationale for keeping trypanotolerant livestock both in tsetse-infested and tsetse-free areas (FAO, 2003). It is anticipated that, as more studies establish the economic viability of trypanotolerant livestock, they will assume a higher profile and hence gain greater acceptance by producers and society at large.

Trade in trypanotolerant livestock in relation to expansion of herd size

The often-stated notion that a shortage of trypanotolerant breeding stock prevents the expansion of trypanotolerant livestock is commonly accepted. This is particularly true if animal numbers need to be established and increased rapidly in unexploited areas of the humid and subhumid zones where they have not previously been raised. However, d’Ieteren (1994) argued that even in years when international trade of trypanotolerant livestock has been at a peak, the availability of stock has been higher than demand for them. Nevertheless, evidence exists that individual countries were unsuccessful in securing the orders of stock they requested from specific exporting countries as a result of inadequate supplies (FAO, 1987). Thus, if farmers can be convinced of the merits of N’Dama and Shorthorns, dissemination of trypanotolerant livestock would appear to be more feasible than may hitherto have been practised (Agyemang et al., 1997).

Trade in trypanotolerant livestock, especially cattle, from countries considered as origins to new countries dates back to the 1920s. The first record of export of trypanotolerant cattle was from Guinea to Belgian Congo (now the Democratic Republic of the Congo) in 1927 (FAO, 1987). There were subsequent exportations to Ghana in 1932 and to Nigeria in 1939. Zaire (now the Democratic Republic of the Congo) became an exporter of trypanotolerant stock in 1973, exporting to Togo. The Gambia, Guinea, Mali and Sierra Leone could be classified as “supply” countries, while the Central African Republic, Gabon, Ghana, Nigeria and Togo are “demand” countries. Benin, Cameroon, the Congo, Côte d’Ivoire and the Democratic Republic of the Congo are “supply/demand” countries, having imported and exported trypanotolerant stock at some time in their livestock development.

Trading in trypanotolerant livestock across country borders in West and Central Africa is believed to be contributing to the increase in regional diversity of these stocks. The possibility of breeds and strains adapting to new species of trypanosomes and consequently being more resistant is enhanced through cross-border trade. The development of export markets, for example to Europe, would not only bring in foreign exchange, but also serve as an incentive to farmers to sustain production. High-quality beef from trypanotolerant livestock on European markets could have a positive impact on the drive to popularize these animals and hopefully link to the support for their wider use and conservation.

Supply and demand fortrypanotolerant stock

Shaw and Hoste (FAO, 1987) and Shaw (1990) developed a herd-modelling tool that uses production parameters and herd dynamics data in a spreadsheet format to calculate potential supply of surplus heifers from national herds. Their model is able to estimate these values over a 15-year period under various scenarios, in sensitivity-type analyses. The use of such an approach in estimating supply, when combined with demand analysis, with options to predict deficits, could be useful in planning the extent of production that would be needed in the future.


Based on existing herd structures, demography, offtake rates and reproduction rates and assuming the maintenance of existing national herd size, Shaw and Hoste (FAO, 1987) calculated for each of the “supply” countries the potential supply of surplus heifers for export from 1985 to 2000. Three scenarios based on optimistic, medium or pessimistic assumptions of production parameters were provided. Therefore, it is possible, at the least, to obtain a theoretical or potential availability of aggregated surplus cows for sale in the region as a whole. If the optimistic production parameters are assumed for each country, the potential surplus of heifers produced per year for the West and Central African region was estimated to be 90 000 head. Using the medium and pessimistic assumptions, the potential surpluses were 53 000 and -9000 (negative herd growth with respect to heifers) per year. Approximately 53 percent of all the potential surplus heifers for export were expected to be N’Dama.


Typically, the export of trypanotolerant cattle from the “supply” countries has occurred as a result of the “demand” countries making the initial requests for these animals. Shaw and Hoste (FAO, 1987) gave details of some of the transactions. In some instances, several sources (countries) were contacted initially by the importing country and a final choice was made based on visits to these countries by technicians to examine the animals.

Shaw and Hoste (FAO, 1987) reported on the prospects of further trade in trypanotolerant cattle in the various countries surveyed. For the majority of the traditionally importing countries, interest in trypanotolerant cattle remained high but invariably the high cost of imports, principally from transportation, has compelled these countries to modify their policies in favour of using indigenous animals available in their own countries. Surplus animals produced on parastatal ranches were to be made available to local producers. In certain countries, the West African Shorthorn breeds were noted to be receiving attention in view of their moderate to high production levels.

It would appear from the stated changes in policy towards importation, the shift in the World Bank’s funding strategy (de Haan, 1988) and the difficulties in generating local funds to support imports that demand for trypanotolerant cattle from the traditional exporting countries is not expected to rise considerably. However, the internal demand occasioned by the establishment of new projects and increased human population in a number of these countries should maintain the need for the development of trypanotolerant stock in the medium and longer term. The overall assessment is that some cross-border trade in trypanotolerant livestock will continue to flourish. However, the large-scale importations from West to Central Africa observed in the 1970s and 1980s are not likely to occur in the next few decades unless the current pattern of funding to support imports changes for the better.

Distribution of trypanotolerant livestock and trends in herd size

The trypanotolerant cattle populations in West and Central Africa for three years, 1975, 1985 and 1998, and annual growth rates are shown in Table 8. There were an estimated 11.68 million trypanotolerant cattle in 1998 of which 11 million were in West Africa and the balance of 0.68 million in Central Africa. The total represented 19.2 percent of the entire cattle population of West and Central Africa, that is 51 million. If the cattle populations of Chad, Mauritania and the Niger are excluded as these countries lie substantially outside the tsetse belt, the percentage of trypanotolerant cattle was 22.9 percent as compared with 26.6 percent in 1985. Overall, the trypanotolerant cattle population grew 1.4 percent (Table 8) during the 14-year period (1985-98) compared with 2.7 percent per annum for the total cattle population. The N’Dama cattle population in the West and Central Africa region in 1998 was estimated to be 5.35 million head and constituted 10.5 percent of the total cattle population compared with 13.1 percent in 1985, when the N’Dama population was 4.86 million. In 1998, N’Dama constituted an estimated 45.7 percent of the total trypanotolerant cattle population compared with 49.5 percent in 1985. There were an estimated 2.53 million head of Savannah Shorthorn cattle in the West and Central Africa region in 1998. They constituted 4.2 and 21.7 percent of the total cattle and trypanotolerant cattle population, respectively. In 1985, when they numbered 1.96 million head, the corresponding shares were 5.3 and 20 percent. There were an estimated 0.15 million head of Dwarf Shorthorns in 1998, a 50 percent increase over the 1985 population of 0.10 million head. The Dwarf Shorthorns represented only 0.29 percent of the total cattle herd and 1.28 percent of the trypanotolerant cattle population. There were an estimated 3.63 million head of Zebu x N’Dama and Zebu x Shorthorn cross-breeds in the West and Central Africa region in 1998. This represented 31.2 percent of the trypanotolerant cattle population and 7.1 percent of the total cattle population. In 1985, they constituted 29 percent of the trypanotolerant cattle population and 7.8 percent of the total cattle population. From 1985 to 1998, the cross-bred population grew at an annual rate of 1.83 percent. The fastest growth occurred in Ghana (6 percent) for the Sanga, Benin (3.2 percent) for the Borgou and in Côte d’Ivoire (3.7 percent) for the Mere.

Trends in trypanotolerant cattle populations

Cattle breed/group




% annual













Savannah Shorthorn






Dwarf Shorthorn












Zebu x N’Dama






Zebu x Shorthorn






All breeds






Sources: Data for 1975 and 1985 from Hoste et al., 1985; data for 1998 from Agyemang, 2000a.

There were an estimated 61.70 million head of sheep in the West and Central Africa region in 1998. Approximately 12.78 million head of this total (20.1 percent) were found in Chad, Mauritania and the Niger. Exclusion of the sheep populations in these countries from the analysis leaves the total sheep population at an estimated 48.92 million head. An estimated 15.78 million head (32 percent) were considered to be trypanotolerant. The corresponding population in 1985 was 12.02 million sheep and hence an estimated annual growth rate of 2.2 percent.

In 1998, there were an estimated 78.13 million head of goats in the West and Central Africa Region. Approximately 15.41 million head of this total (19.7 percent) were found in Chad, Mauritania and the Niger. If the goat populations in these countries are excluded from the analysis, the total goat population is an estimated 62.72 million head. An estimated 29.39 million head (46.9 percent) were considered to be trypanotolerant as compared with 19.94 million head in 1985. From 1985 to 1998 the estimated annual growth rate was 3.5 percent (Agyemang, 2000a).


Interest in the utilization of trypanotolerant livestock in West and Central Africa is linked to the general desire of governments in the subregion both to reduce the domestic shortage of meat and to promote exports of breeding stock at attractive prices (ILCA, 1979a, b). This goal has been pursued through several options, including the extension of basic animal production into new areas, diversification (e.g. draught oxen and milk production), stratification (e.g. fattening by smallholders and on feedlots) and improved organization such as meat processing to increase quality and shelf life. A slightly different approach was adopted in the 1970s in West Africa from that in Central Africa. In the former, the improvement and extension of cattle husbandry at the village level usually involved improved management, introducing veterinary packages and supplying improved breeding stock, mostly the N’Dama. In the latter area, where cattle production at the village level was not a traditional occupation, the métayage system was adopted whereby development started with the loan of foundation breeding stock, followed by support activities (ILCA, 1979a).

It became apparent to the ILCA study team that evaluated the status of trypanotolerant livestock in the late 1970s that the continued promotion of the utilization of these breeds of livestock would generally depend on the demonstration of their productivity relative to other breeds. Although such a demonstration would be based on data compiled from various production systems in the countries surveyed, more convincing evidence would come from comparative studies involving tolerant and susceptible breeds, accounting for all the costs involved in tsetse control, chemotherapy and chemoprophylaxis. The ILCA 1979 study concluded that “...the demonstration of the biological and commercial success of trypanotolerant breeds could open the way for their introduction into wide stretches of savannah which are at present (1978) almost empty of cattle”. The moderate growth rates in trypanotolerant livestock, especially in small ruminants, shown in the earlier sections, indicate that these breeds will continue to be used in the production systems as pure breeds or cross-breeds. However, if steps are not taken, the cross-bred population component will expand faster than the pure breeds. The wider use of these genetic resources in many production systems directly ensures their continued conservation. Indirectly, wider use influences preference and hence the value of the animals, which consequently encourages conservation.


Conservation of animal genetic resources has been justified on at least three grounds (Cunningham, 1992). First, the drive to replace the less productive with more productive breeds or strains of livestock should be tempered by the realization that the production circumstances and market requirements around the world vary so much that a variety of breeds and types is needed within any one species. Second, in any one set of production and market conditions, requirements change over time, thereby making availability of variety necessary. Third, the preservation of genes and gene combinations, whose value may currently be unknown, may have great value in the future. While the conservation approach in European countries has taken the form of the protection of rare breeds, Hall (1992) considered “... the rational use and protection of existing local genotypes from genetic introgression” to be a more appropriate definition of conservation in the context of sustainable livestock development in Africa. In the particular case of trypanotolerant livestock, the superior ecosystem health resulting from avoidance of using chemicals to control vector and parasites and the sparing of clearing forest to rid the tsetse vector provides another strong argument for their conservation and continued use.

Cunningham (1992) noted that many developing countries had placed their indigenous livestock populations at risk through programmes of exotic breed importation and/or cross-breeding. In most of these countries it was said that attention was rarely paid to the evaluation and setting up of optimum breeding objectives prior to the implementation of breeding programmes, usually resulting in inappropriate schemes. There is some suggestion that cross-breeding involving exotic breeds is attractive to some developing country governments because aid agencies are willing to fund such schemes (Hall, 1992).

Recent calls for the conservation of indigenous animal genetic resources and their endemic habitats as a way to stem the threats to their existence appear to be being heeded by national governments and the international community, as illustrated by donors’ interest in considering funding of regional initiatives in this field of development (Agyemang, 2000a). The overall assessment is that governments in the region and other stakeholders will continue to take conservation of animal genetic resources, including trypanotolerant livestock, more seriously in the future than was the case in the past.

Scientific breakthroughs in chemical-based technologies for trypanosomiasis control and selective breeding programmes

The possibility of discovering newer drugs and the development of vaccines for the control of trypanosomiasis have often been considered as a potential breakthrough in the quest for reducing the tsetse-trypanosomiasis problem. It has been reported that no major new drug for the treatment of trypanosomiasis has been released on the market over the past 20-30 years (Budd, 1999). Similarly, no new drugs are currently in the pipeline for manufacturing (d’Ieteren et al., 1998). Possibilities for newer drugs appear to depend on certain pharmaceutical firms being encouraged or induced to make decisions on manufacturing based not purely on early profit-making but on other welfare considerations, as is being advocated for drugs for treating major diseases such as HIV/AIDS and malaria affecting humans. With respect to the discovery of effective anti-parasite vaccines against trypanosomiasis, the setbacks arising from the antigenic variation of trypanosomes raise doubts of early breakthroughs in that line of scientific investigation. However, there are medium to high prospects in the line of research on the development of strategies to increase resistance to trypanosomiasis based on the use of trypanosome cysteine proteases as antigens, which may lead to exploitation as an anti-disease vaccine (Authié, 1994). However, the time frame for the delivery of such a product is unknown.

In the field of genetic improvement of both indigenous and exotic livestock with respect to tolerance to major diseases, especially trypanosomiasis, efforts on both conventional selective breeding and genotypic (DNA) marker-assisted breeding programmes are ongoing in certain locations that could lead to increasing the number of animals with some level of tolerance as pure breeds or cross-breeds. The possibilities of introducing disease-tolerant or disease-resistant genes identified from genetic markers into higher production merit animals that are otherwise susceptible could also increase the populations of trypanotolerant livestock in and outside the tsetse-infested zones. With advances in biotechnology, particularly in genome mapping, these possibilities may translate into reality. However, the exact time period for this is difficult to predict.

Moreover, the new possibilities of making direct analyses of genetic variation at the DNA level (molecular markers) have given rise to several techniques that are useful or potentially useful in population studies, including gene distancing, gene flows and admixtures. Applications of such methods (e.g. restriction fragment length polymorphism [RFLPS], Mitochondria DNA analyses, major histocompatibility complex [MHC], Y-Chromosome DNA analyses) have already been applied to African cattle, facilitating, for example, the identification of pure trypanotolerant livestock as opposed to genetically-mixed ones (Bradley et al., 1996). These results have direct implications for the rate at which progress can be achieved in breeding programmes involving trypanotolerant livestock.

Previous Page Top of Page Next Page