Chapter 2. REVIEW OF LIVESTOCK AGRICULTURE IN THE CONTEXT OF TRYPANOSOMIASIS

Overview of the political and agricultural economy of West and Central Africa

The West and Central Africa subregion of sub-Saharan Africa (SSA) consists of 22 independent sovereign countries (excluding the islands of Cape Verde, Saint Helena and Sao Tome and Principe) stretching from Mauritania on the west African coast (latitude 28° 00’ at its northernmost border with Algeria) to the Democratic Republic of the Congo (formerly the Republic of Zaire) to the east (longitude 30° 00’ at its easternmost border with the United Republic of Tanzania and latitude 21° 00’ at its southernmost border with Zambia). Between these two countries lie, roughly from west to east and along the coastal strip, Senegal, the Gambia, Guinea-Bissau, Guinea, Sierra Leone, Liberia, Côte d’Ivoire, Ghana, Togo, Benin, Nigeria, Cameroon, Equatorial Guinea, Gabon and the Congo, all with border access to the Atlantic Ocean. Burkina Faso, the Central African Republic, Chad, Mali and the Niger are landlocked. Benin, Burkina Faso, Côte d’Ivoire, the Gambia, Ghana, Guinea, Guinea-Bissau, Liberia, Mali, Mauritania, the Niger, Nigeria, Senegal, Sierra Leone and Togo are in West Africa while Cameroon, the Central African Republic, Chad, the Congo, the Democratic Republic of the Congo, Equatorial Guinea and Gabon are in Central Africa. The total land surface for the countries in the region is approximately 11.5 million km² and represents about 37 percent of Africa as a whole.

The total human population for the region in 1999 was approximately 317 million or 50.3 percent of the SSA total (PRB, 1999). Overall human population growth during the 1990s was estimated at 2.8 percent per annum, and in urban areas at about 6 percent. Whereas the population “doubling time” in SSA as a whole is calculated to be 27 years, in West and Central Africa the figures are 24 and 23 years, respectively. Thus, growth rates in West and Central Africa are considered to be the fastest for any region of SSA. From the 1990 population growth rate of 2.8-3 percent, it is projected that the population will have reached 596 million by 2025 (Aryeetey-Attoh, 1998; PRB, 1999).

All the 15 countries of West Africa, except Mauritania, belong to the Economic Community of West African States (ECOWAS) whose major goal is to foster the economic integration of the countries in the region. This goal calls for the free movement of people and goods, including livestock. In pursuance of this objective, the heads of state of member countries signed a protocol in 1998 that grants travel certificates to owners of herds and flocks of livestock to facilitate seasonal migrations across the common borders of these countries. In addition to ECOWAS, the French-speaking countries in the region have a regional monetary and economic community of their own, the Union Économique et Monétaire Ouest Africaine (UEMOA). Within this association is the livestock group, Communauté Économique du Bétail et de la Viande, which also issues international certificates for transhumance to livestock breeders to enable them to move freely in the region with their livestock (ECOWAS, 1999).

As in many countries in other regions of SSA, agriculture forms the backbone of the economies of countries in West and Central Africa. Approximately 50-80 percent of the workforce in several of the countries is engaged in the agriculture sector. Agricultural production contributes 30-50 percent of the gross domestic product (GDP) in most of these countries. Livestock production contributes about 20-25 percent of the agricultural GDP and ruminant livestock products, namely meat and milk, are important components in the diet of most people. Due to the increase in human population and projected urbanization, the growth in demand for these products will be even greater than that for crop-based food. For example, demand for dairy products in several countries in the region is expected to double by 2010 (Nicholson et al., 1999). Most of these increases in demand will have to be met from indigenous production using local animals.

It is already evident in several countries that human demographic factors are exerting significant pressures on the cultivatable land, resulting in reduced fallow periods and degradation in some instances. Agricultural productivity per capita in West Africa declined from the 1950s to the mid-1980s (World Bank, 1984). There have since been some increases in a few selected crops but these were achieved largely through expansion in upland areas under cultivation. The growth rate in food production must increase by at least 3 to 3.5 percent annually to bridge the gap between demand and supply. There is, however, some evidence that suitable uplands, where expansion in food production has traditionally occurred, are becoming scarce in the region (Thenkabail and Nolte, 1995; Windmeijer, van Duivenbooden and Andriesse, 1994). It has been suggested, and is generally being accepted by policy-makers, that perhaps the most sustainable means of increasing land productivity is the intensification of agriculture through a greater integration of crop and livestock production or mixed crop-livestock farming (McIntire, Bourzat and Pingalli, 1992; Winrock, 1992).

Livestock in the agricultural and rural economy

In view of the soil degradation and reduced land productivity noted above, the traditional role of livestock in providing animal draught power for cultivation, weed control and harvesting would need to be expanded into new areas and made more efficient in areas where it is already practised (de Haan, 1988). Similarly, the collection and storage of manure and urine from livestock for crop production, which is a major input in drier subhumid and semi-arid areas (Powell, Fernández-Rivera and Höfs, 1994), would need to be made more efficient (Fernández-Rivera et al., 1995). There is also some evidence that income from the sale of livestock and products, which could be as high as 78 percent of the income from crop-livestock farms (Debrah and Sissoko, 1990), is used to support crop production (Brumby, 1986). These statistics show that the contribution of ruminant livestock to agricultural development in the region is already substantial.

Thus, taking into consideration the projected demand for livestock products and the need for sustainable agricultural production, livestock genetic resources will be expected to play increasingly more important roles in the agricultural and social economies of West and Central Africa. Winrock (1992) estimates that a 4 percent annual growth rate in milk output and a 3.4 percent growth rate in red meat would be required in SSA as a whole to meet the projected demand for these products. In a more recent assessment, Delgado et al. (1999) calculated the annual growth of total production of milk and meat in SSA from 1993 to 2020 to be 4 percent and 3.4 percent, respectively. Total production in 2020 is expected to be 31 and 11 million tonnes for milk and meat, respectively. However, real concerns have been expressed about the prospects and the capacity of the current animal genetic resources to meet their expanded roles in the future. For example, the current productivity of the indigenous livestock, which constitute the overwhelming majority of all livestock in the region, is considered to be low due largely to nutritional (poor quality of feed and seasonal scarcity) and disease stresses. Other major constraints are market failures and imperfections resulting from a lack of incentives and reward systems for producers, undeveloped inputs and outputs markets, and the absence of flexible agricultural policies.

The central role of livestock agriculture as an engine for rural development and sustainable food and nutritional security for rural and peri-urban households has, however, been documented (Abassa, 1995; Agyemang, 2000b). It is almost universally accepted that the market-related and biological constraints listed above need to be reduced or removed in order to maximize the benefits from livestock-based development. Of the biological constraints, inadequate nutrition and suboptimum animal health are considered to be the major hindrances.

Trypanotolerant livestock and their productivity

Of the several epizootic diseases (gastrointestinal parasitism, ectoparasitism, etc.) that plague livestock agriculture in SSA, and for that matter West and Central Africa, trypanosomiasis is argued to be the single most important constraint to animal agriculture in the subhumid and non-forested portions of the humid zones of Africa. The disease has both direct and indirect economic impacts on livestock production. The direct impacts are associated with losses of milk and meat production as well as mortality and morbidity. The indirect impact is related to the opportunity cost of land and other resources currently not used for livestock production owing to the presence of tsetse flies. In 1963, the annual loss in meat production alone was estimated at US$5 billion (Murray and Gray, 1984). Murray et al. (1991) considered that if such losses in milk and manure production and traction power could be prevented, the benefit from livestock and mixed agricultural developments in tsetse-infested Africa could amount to US$50 billion annually and, with the paucity of reliable data, even this figure could be an underestimate. It has been estimated that about 37 percent of the continent, or 11 million km² involving 37 countries, is infested with tsetse (FAO/WHO/OIE, 1982) and that approximately 65 percent of this area (7 million km²) could be used for livestock or mixed agriculture development without stress to the environment if trypanosomiasis was controlled (MacLennan, 1980).

The exploitation of the genetic resistance to trypanosomiasis through the use of indigenous, tolerant ruminant livestock is one approach to the control of the disease. The option of using these livestock breeds, thus reducing or eliminating the use of chemicals for controlling the vector and parasites, contributes positively to a balanced ecosystem health. Livestock breeds that possess the ability to survive, reproduce and remain productive under trypanosomiasis risk without recourse to trypanocidal drugs are said to exhibit trypanotolerance and are referred to as trypanotolerant. This ability is exhibited to the highest degree in a few breeds of cattle in West and Central Africa, namely N’Dama and West African Shorthorns, as well as Djallonke sheep and goats, also found in the region.

Although the trypanotolerance of N’Dama and West African Shorthorn cattle has long been recognized - and indeed experimental studies comparing N’Dama and Zebu breeds have confirmed this (Dwinger et al., 1994) - these breeds represent only a small proportion (6 percent) of the cattle population of Africa and only 17 percent of the total cattle population in the affected areas. In 1985, there were only an estimated 9.8 million trypanotolerant cattle in West and Central Africa. Trypanotolerant sheep and goats were more numerous and numbered approximately 12.0 and 19.9 million, respectively. These represented 41 and 43 percent of the sheep and goat populations, respectively. By 1998 the trypanotolerant cattle population had grown to 11.7 million head. The trypanotolerant sheep and goat populations in 1998 were 15.8 and 29.4 million, respectively.

It has been postulated that the low number of these animals in Africa, despite their unique ability to withstand trypanosomiasis and possibly other parasitic infections (Claxton and Leperre, 1991), is due in part to the widely held belief that they are not productive because of their relatively small size. This belief was shown to be incorrect following a survey of trypanotolerant livestock in 18 countries in West and Central Africa in 1978 by the International Livestock Centre for Africa (ILCA), the Food and Agriculture Organization of the United Nations (FAO) and the United Nations Environment Programme (ILCA, 1979a, b). This study compared the productivity of different breeds based on body weight, calving rate and mortality, and found that in areas where tsetse fly risk was low, the productivity of N’Dama and West African Shorthorn cattle was only marginally below that of Zebu. A similar comparison in areas of medium to high tsetse challenge was not possible because only trypanotolerant livestock were present. Tables 1 to 3 show comparisons between trypanotolerant and trypanosusceptible breeds of livestock under various production systems and tsetse challenge.

Under station management conditions in the humid zone of Nigeria where tsetse was controlled, cow viability among N’Dama, Shorthorn and Zebu were similar, while the calving percentage was superior in the trypanotolerant stock (average 98 percent) to that of Zebu (91 percent). Although the average cow weight of Zebu was as much as 30-80 percent heavier than the tolerant breeds (Table 1), on the basis of a productivity index, which combines several production and viability traits, the Zebu was only 7 percent superior to the tolerant breeds. In medium tsetse-risk situations in village production systems in the Central African Republic, the productivity index of Shorthorn cattle exceeded that of Zebu by 44 percent. Agyemang et al. (1997) demonstrated that if milk production from trypanotolerant cattle is included in the calculation of productivity indices, the overall index for village production systems in the Gambia exceeded several Zebu-based traditional production systems in Africa by 30-60 percent (Table 2).

TABLE 1
Productivity of trypanotolerant and Zebu cattle in three locations at different levels of tsetse challenge and management

Notes: a) Central African Republic; b) N’Dama; c) Shorthorn; d) Zebu; e) total weight of one-year-old calf plus live weight equivalent of milk produced per 100 kg of cow live weight maintained; - means not applicable.
Source: ILCA, 1979a (reproduced in Jahnke, 1982).

In the case of small ruminants, the figures in Table 3 clearly demonstrate that the productivity of trypanotolerant sheep and goat breeds (Djallonke sheep and West African Dwarf goats) maintained under tsetse fly-infested conditions was 42 and 68 percent, respectively, higher than susceptible breeds, even when the susceptible breeds were kept in tsetse fly-free environments. Many of the trypanosusceptible breeds do not survive in tsetse-infested areas. The higher productivity of trypanotolerant small ruminants was also demonstrated in flocks of sheep and goats in traditional systems in the Gambia (Agyemang et al., 1991a).

The essence of the data presented in the tables referred to above is that trypanotolerant livestock are highly productive and compare favourably with the larger but otherwise susceptible breeds under zero to low tsetse challenge conditions. Under medium to high tsetse challenge, trypanotolerant breeds are more productive than susceptible breeds. In a recent economic analysis of production systems, Shaw (FAO, 2003) demonstrated that output per head of cattle in trypanotolerant herds per year was US$93 in tsetse-infested environments and was 39 percent (US$67) and 26 percent (US$74) higher than those in transhumant and sedentary mixed herds in similar environments, respectively (Table 4). The corresponding figures in tsetse-free environments for output per head per year were US$99, US$75 and US$86, showing that trypanotolerant livestock were 32 percent and 15 percent more productive than susceptible transhumant and mixed herds, respectively. Thus, there is both a biological and economic justification for keeping trypanotolerant livestock.

TABLE 2
Comparison of productivity indices* of N’Dama and Zebu cattle kept in various production systems in Africa

*weight of a 12-month-old calf plus live weight equivalent of lactation milk offtake for human use
Sources: 1. Agyemang et al., 1997. 2. Wagenaar, Diallo and Sayers, 1986. 3. Otchere, 1983. 4. Wilson, 1989. 5. De Ridder and Wagenaar, 1986.

As pointed out above, although the discovery that certain breeds of cattle are able to survive in tsetse-infested areas where other breeds rapidly succumb was made as long ago as the early 1900s (e.g. Pierre, 1906), doubts still persisted as to whether this ability was merely transient in view of the stress factors that affected the susceptibility of these so-called trypanotolerant breeds. For example, in the light of the observations of occasional susceptibility found in field situations, it was believed by some that the resistance of trypanotolerant breeds was largely the result of acquired immunity to local trypanosome populations and that the “tolerance” would break down if cattle were moved (Murray, 1988). Several reports on the successful movement of trypanotolerant cattle over large distances into tsetse areas (Ferguson, 1967; Mortelmans and Kageruka, 1976; Stewart, 1951) and the continued evidence of trypanotolerance by these relocated animals have not only shown that the trait is innate, but also that trypanotolerance has a genetic basis (that is, can be passed on from parents to offspring) and that the attribute is enhanced further by continued exposures to the parasite.

TABLE 3
Production traits of trypanotolerant and non-tolerant groups of sheep and goats

Source: ILCA, 1979a (reproduced in Jahnke, 1982).

TABLE 4
Comparison of biological and economic performance of susceptible cattle herds (in transhumant and sedentary systems) and trypanotolerant herds in tsetse-free and tsetse-infested environments

Note: tryps = trypanosomiasis.
Source: FAO, 2003.

Many governments in the region have responded to the option of using trypanotolerant livestock in combating the threat of tsetse-transmitted trypanosomiasis, as evidenced by the large number of externally-funded projects executed during the 1970s and 1980s (ILCA, 1979a; de Haan, 1988) and the continued consideration of trypanotolerant stock in integrated agricultural projects (FAO, 1987).

Multidisease resistance

In a recent review, d’Ieteren et al. (1998) summarized the current knowledge on the new number of diseases to which trypanotolerant livestock are believed to show some level of tolerance or resistance. The review established that:

in addition to their resistance to trypanosomosis, trypanotolerant cattle, and the N’Dama breed in particular, have other genetic advantages that contribute to their potential for use in livestock development programmes in the tropics. These cattle are reported to be resistant to several other important infectious diseases (Murray et al., 1991), including a number of tick-borne infections such as dermatophilosis, heartwater, bovine anaplasmosis and bovine babesiosis (Epstein, 1971). Lower tick burdens have been reported recently in N’Dama cattle in comparison with zebu cattle (Claxton and Leperre, 1991; Mattioli et al., 1993). Mattioli, Cassama and Kora (1992) also reported that N’Dama cattle showed lower prevalence of strongyle infections, and when infested by strongyles, lower egg outputs, than the Gobra zebu cattle. More recent research at the International Trypanotolerance Centre, the Gambia, also provided evidence of the greater resistance to heartwater and other tick borne diseases in N’Dama cattle compared to Gobra zebu (Mattioli et al., 1994; 2000).

Heat tolerance and water metabolism attributes of trypanotolerant cattle

It has been reported that trypanotolerant cattle, especially the N’Dama cattle breed, show superior heat tolerance when compared with Zebu cattle. This desirable attribute is particularly useful under the high temperature-high humidity regimes encountered in semi-arid and subhumid conditions in West Africa, where most ruminant livestock must roam for food and water during most of the year. The economy in water metabolism found in certain breeds of trypanotolerant livestock, particularly in N’Dama cattle, is yet another favourable attribute, especially in water-deficit environments.

Trypanotolerance and the future of agriculture in West and Central Africa

The brief overview in the previous sections indicates that trypanotolerance as exhibited by certain cattle, goat and sheep breeds in West and Central Africa is an innate trait that currently ensures the existence of a significant amount of diversity in animal genetic resources in the region. They offer prospects for livestock agriculture in new areas where other livestock breeds cannot survive. However, the expansion in numbers of these relatively few animal genetic resources, especially of the cattle breeds, is not guaranteed because of threats of replacement and assimilation. Ironically, the diversity in animal genetic resources created by the presence of these breeds and strains of trypanotolerant stock stands to erode this diversity as the more prominent among them, for example the N’Dama cattle, are more vigorously and extensively promoted at the expense of the less popular breeds. Individual farmers, exercising their right to choose, prefer breeds that may inadvertently be breeding out valuable genotypes (Kamuanga et al., 1999). Unfortunately, it is not only individual farmers that are engaged in this short-term maximization of genes from the few popular breeds; government farms and stations are also involved. More carefully planned breeding policies in the region would curb this indiscriminate upgrading and replacement.

Thus, for an assured future presence and use of these unique resources, a balanced utilization strategy that ensures the conservation of all breeds and strains is needed. It has been argued that genes, which do not have commercial value currently, may become important in the future (Cunningham, 1992). It has further been argued that the most rational and sustainable way to conserve animal genetic resources is to ensure that indigenous breeds remain functional parts of the production systems and thereby permit the identification and incorporation of economically important traits in breeding programmes (Rege, 1999). Indeed, it is said that the future utilization of the genetic resources represented by trypanotolerant cattle to harvest the biomass of much of humid sub-Saharan Africa depends on their conservation, promotion and improvement (FAO, 1992; FAO, 1993).

Government restrictions on movement of trypanotolerant stock: the embryo transfer experience

Although active trade in trypanotolerant livestock between West and Central Africa dates back to the 1920s, the development of such trade between Central and East Africa and between West and East Africa has been hampered to date by regulatory or phytosanitory laws governing the cross-border transportation of biological materials into East African states, particularly Kenya. In 1985, however, despite these laws, frozen embryos of N’Dama cows were introduced into Kenya for transfer into Boran surrogate mothers raised at the International Laboratory for Research on Animal Diseases (ILRAD) in Nairobi (Jordt et al., 1986). This measure was in response to the need for well-established laboratories in East Africa to undertake studies to determine and understand the genetic and molecular bases of the trypanotolerance attributes. It enabled the first N’Dama herd to be established in the region, allowing, in turn, its use for comparative studies and also for producing F1 and backcross generations required for quantitative trait loci studies. Whether embryo transfer offers an economically viable option for introducing large numbers of trypanotolerant livestock to new areas remains to be seen.