Chapter 5. FRAMEWORK FOR ANALYSING THE ROLE OF TRYPANOTOLERANT LIVESTOCK

In reviewing key strategies for developing the livestock sector in sub-Saharan Africa, Jahnke et al. (1988) noted that trypanosomiasis acts as an environmental constraint reducing productivity or even making large rangeland areas unsuitable for livestock production. The choice among the three main practices in combating tsetse-trypanosomiasis (tsetse control or eradication, chemical treatment or prophylaxis and the use of trypanotolerant breeds) was said to depend on local conditions, in particular:

• the existing situation of livestock husbandry (breeds used, production systems, etc.);

• the level of trypanosomiasis challenge and whether it is permanent or seasonal; and

• the ranking and relative importance of trypanosomiasis among other development constraints.

With respect to existing livestock husbandry practices, the production systems adopted, breeds used, etc. are usually determined by the larger ecological setting, but are also influenced by the existence of special niches (geographical, markets, etc.).

From the discussions in the preceding sections, it appears that, in addition to physical and socio-economic factors (e.g. presence of trypanotolerant stock, their utilization, conservation, trade, economic generation of wealth from these stock, etc.) that enable trypanotolerant stock to provide alternative and complementary livestock production in tsetse-infested areas, there is a biological basis for the use of trypanotolerant livestock in reducing parasite loads and transmission rates in a given area.

The overview presented in the previous sections also indicates that the perceived or actual roles trypanotolerant livestock play in the wider context of trypanosomiasis control are very much dependent on the production systems in which they are found, the extent of usage of other control methods and options, the population size of trypanotolerant livestock in a given agro-ecological zone and perceived or imputed value of the these breeds relative to other (trypanosusceptible) breeds. Since these factors or elements of them are variable over time, an analytical framework is proposed (a 3 x 3 matrix) that considers the temporal element (past, present and future) with respect to knowledge, perceptions, technology, etc., on one axis, and ecological zone/production system on the other (semi-arid, subhumid and humid zones) where tsetse infestation poses a considerable constraint on livestock production.

TABLE 9A
Suggested framework for analysing the role of trypanotolerant livestock in the context of methodological

The proposed framework could incorporate additional subfactors within the main factors defined by the 3 x 3 matrix. For the temporal factor, the past (before 1970), present (1970-2010) and future (2010-30) can each be embedded with subfactors, namely, (1) numerical strength of trypanotolerant livestock; (2) control measures available, state of knowledge and potential advancement in techniques; (3) societal perceptions of value of trypanotolerant stock; and (4) research and development efforts relative to conservation, biotechnological and selective breeding and improvements in trypanotolerant livestock. For the agro-ecological zones dimension, the shift or gradual development from low-input, traditional systems to medium- or high-input market-oriented systems (MOS), and how they relate to use or potential use of trypanotolerant livestock or cross-breeds derived from them can be captured by considering two production systems: the extensive, low-input system and the crop-livestock system. Over a period of time there is a tendency for some of the extensive low-input systems to develop into crop-livestock systems. Similarly, where market demand and production inputs become increasingly available, some of the highly developed crop-livestock systems evolve into market-oriented systems. A suggested framework with the factors and subfactors discussed above is given in Tables 9A, 9B and 9C for the past, present and future temporal dimension, respectively.

TABLE 9B
Suggested framework for analysing the role of trypanotolerant livestock in the context of methodological trypanosomiasis control/eradication in West Africa: present (1970-2010)

* sterile insect technique

EXPECTED RESPONSES TO CONTROL OPTIONS IN CHANGING PHYSICAL, SOCIO-ECONOMIC AND TECHNOLOGICAL ENVIRONMENTS

The summary information in Table 9B suggests that in the extensive, low-input production systems of the semi-arid ecozone, trypanotolerant livestock do not currently appear to have a significant role as a control option for tsetse-trypanosomiasis. This was also true in the past (prior to 1970; Table 9A), when there were fewer trypanotolerant livestock. Currently, chemical-based therapy for susceptible breeds is the preferred option (Budd, 1999). Should long-term improvement in rainfall lead to an upsurge in the level of tsetse challenge, higher use of chemical-based treatments can be expected (Table 10). On the other hand, in the crop-livestock systems, and particularly in niches geared towards market-oriented production, combinations of drug-based therapies and the use of tolerant-based cross-breeds can be expected. In the event that the level of tsetse challenge decreases, for example as a result of human settlement, a return to the use of susceptible breeds is likely except in enclaves where cross-breeds have developed special niches, for example draught power. An increase in tsetse challenge, on the other hand, might lead to a short-term increase in the use of chemical-based strategies. In the longer term, the prospects for using tolerant-based cross-breeds will increase.

In the low-input, extensive-range systems within subhumid zones, combinations of drug-based therapies and reliance on tolerant stock are expected to continue. Should there be an increase in the level of tsetse challenge, control methods such as traps could be deployed on a limited scale, together with pure and tolerant-based cross-breeds, complemented with chemotherapy and chemoprophylaxis, which would be the preferred option. A reduction in tsetse challenge would lead to drug-based therapies and the use of cross-breeds in special niches (Table 10).

In market-oriented crop-livestock systems and subsystems, a limited deployment of modern tsetse control methods combined with the use of tolerant-based breeds, while reducing drug-based therapies, appears to be a sustainable option. Should the level of tsetse challenge increase in pockets and riverine areas, the deployment of limited tsetse control measures will be an option, especially where the expected benefits from increased production far outweigh the cost of control. However, the use of tolerant and tolerant x local crossbreeds supported by chemotherapy will assume greater importance. In the event that there is a drastic reduction in tsetse challenge in areas heavily populated by humans, the use of cross-breeds (exotic x tolerant) together with chemotherapy will be an option.

TABLE 9C
Suggested framework for analysing the role of trypanotolerant livestock in the context of methodological trypanosomiasis control/eradication in West Africa: future (2010-2030)

TABLE 10
Expected responses to control options in changing physical, socio-economic and technological environments

With respect to the humid zone, reliance on the use of tolerant stock will continue to be the favoured option. In the non-forested parts of the humid zone, additional functions such as draught power from tolerant breeds of cattle may impose stress and/or inadequate nutrition may lead to nutritional stress. In such situations, chemotherapy and small-scale tsetse control may be justified. A decrease in tsetse challenge is likely to lead to an influx of susceptible breeds. In the longer term, cross-breeding with tolerant stock might result in the use of more tolerant stock (cross-breeds) together with local tolerant stock. In areas where crop-livestock or market-oriented subsystems have advanced, the use of exotic x tolerant cross-breeds may be expected. An increased risk of higher tsetse challenge will call for greater reliance on trypanotolerant livestock complemented with drug-based treatments. In market-oriented subsystems, limited tsetse control may be justified.

Similar deductions can be made from the information in Table 9C, which takes into account the possibility that research innovations on breeding for trypanotolerance and perhaps an anti-disease vaccine may be forthcoming. In the scenario that technological breakthroughs in breeding techniques lead to a more rapid multiplication of trypanotolerant stock and/or transfer of tolerant genes into susceptible breeds, the need for chemical-based treatments will decrease and the use of tolerant breeds in integrated control schemes will become more prominent. The type of tolerant stock used will, however, depend on the market environments. The availability of an effective vaccine against trypanosomiasis could protect more susceptible breeds in infested areas and could influence the choice of breeds by producers. The role of trypanotolerant stock may diminish as a consequence. However, since trypanotolerant stock are also reported to tolerate other diseases, their overall prominence may not change that much, especially in disease-endemic regions.

It would appear from the technical point of view that area-wide tsetse control can become more widespread, at least in priority production systems in the next two to three decades. Should financial support for eradicating tsetse flies become available, the tsetse challenge will be reduced in several locations. However, the combination of factors, namely the recognition of trypanotolerant stock for their resistance/tolerance to other diseases and production and work capacities of trypanotolerant-based cross-breeds, will ensure their continued use in both extensive and intensive production systems.