But the full potential of mixed farming is limited by the presence of animal trypanosomiasis, a parasitic livestock disease transmitted by tsetse flies, which causes early death or long-term debilitation. Trypanosomiasis now affects about one-third of Africa's total land area, and threatens an estimated 50 million cattle in 37 countries. The risk is most serious in the sub-humid zone and wetter parts of the semi-arid zone, which hold the continent's greatest potential for agricultural expansion.
Yet, despite the disease's importance, relatively little is known about its impacts on overall livestock production and its indirect effects on human settlement, land use and crop agriculture. To fill that gap, a new report prepared for the Programme Against African Trypanosomiasis (PAAT), led by FAO, IAEA, OAU/IBAR and WHO, drew on 10 years of field studies to estimate the full costs of trypanosomiasis for farmers, livestock owners and African countries in general.
Impacts of trypanosomiasis on African agriculture says the most obvious direct impact is seen in the birth and mortality rates of young animals. In susceptible cattle breeds, the disease reduces calving by up to 20%, and causes the deaths of another 20% of calves that are born. Even so-called "trypanotolerant" animals are affected - studies in the Gambia indicate that trypanosomiasis reduces milk offtake by up to 26%, and reduces lambing and kidding rates by as much as 37%.
Using simulation models to assess the costs and benefits of tsetse control, researchers have found that trypanosomiasis significantly reduces herd productivity as well. One study in the Sideradougou area of southern Burkina Faso estimated that cattle population would increase by about 1% a year without tsetse control, but by up to 5% a year with control measures.
Sick oxen less efficient. The disease also reduces the availability and efficiency of draught animals used for preparing land for crops. Data collected from Ethiopia's Ghibe Valley - an area where tsetse control has been successful - and a neighbouring area still affected by tsetse infestation found that oxen in the high risk area are 33% less efficient than those in low risk ones. This has implications for both crop production and general economic development - studies show that farm households using animal traction are generally more productive than those without.
Seasonal fluctuations in the density of tsetse have implications for grazing patterns which, in turn, can provoke disputes among different types of land users. During the rainy season in northern Côte d'Ivoire, for example, Fulani herders move their cattle away from major rivers to upland agricultural areas, resulting in increased conflict with sedentary farmers. Finally, African farmers and governments must bear the increasing cost of treating cattle exposed to trypanosomiasis. Every year, they spend at least $30 million administering between 25 and 30 million curative and prophylactic treatments. Interviews conducted across northern Côte d'Ivoire showed that all households that undertook seasonal transhumance used trypanocidal drugs.
The report also throws new light on trypanosomiasis impacts on human migration and settlement, as well as farming systems in Africa. Expansion of animal trypanosomiasis into a new area can lead to massive out-migration and abandonment of settlements. In a survey in the Zambezi Valley of Zimbabwe, a third of households reported that tsetse infestation had an important influence on where to they decided to settle.
PAAT will support initiatives for national and regional programmes throughout the tsetse-infested regions of Africa. Among priority issues to be addressed are:
Economic development of tsetse-infested areas that does not result in degradation of the natural resource base. Tsetse and trypanosomiasis control will be an essential component.
Research on the socio-economic and environmental impacts of trypanosomiasis and integrated disease management strategies.
Participation of livestock owners in the planning of control operations. The involvement of national researchers, NGOs and the private sector in sub-regional programmes will also be encouraged.
Land degradation resulting from trypanosomiasis control and subsequent overstocking - national governments, which have ultimate responsibility for land use, must be fully
involved in planning.
Agricultural GDP falls. The PAAT report found that, in mixed crop-livestock systems, trypanosomiasis can have several indirect impacts on crop production, in addition to its effects on the efficiency and availability of animal traction. Estimates of the elasticity of agricultural production with respect to livestock show that a 1% increase in a country's livestock holdings is associated with a 0.23% increase in agricultural output. For the semi-arid, sub-humid and humid tropics, changes in stocks of livestock contributed about 19%, 16%, and 20% of total agricultural output growth between 1973 and 1985. Based on these estimates, the report estimates that in countries completely infested by tsetse, trypanosomiasis could reduce agricultural gross domestic product by between 2% and 10%.
The report concludes: "Evidence accumulated over the last 10 years supports claims that trypanosomiasis is an important constraint on agricultural production in Africa. It directly limits the productivity of cattle, sheep and goats and also shapes farmers' choices about the size and structure of their cattle herds and their use of tsetse habitat for grazing. On aggregate, trypanosomiasis is likely to reduce the total livestock holdings by about 10% to 50%". In mixed crop-livestock systems, reductions in the number and work efficiency of oxen have subsequent effects on crop production. Total cropped area is limited, and in some areas yields and responses to new economic incentives are also reduced.
"Unfortunately," the report says, "assessments of the impacts of trypanosomiasis on farming are constrained by a paucity of quantitative information. The handful of systematic studies of the impacts of trypanosomiasis and its control - for example, Ethiopia, The Gambia and in Zaire - are only relevant for specific production systems and disease risk situations.
"Needed is an approach that provides a more systematic coverage of key production systems and disease risk situations. This approach should begin with a systematic typification of production system/disease risk types, a GIS characterization of the geographical distribution of those types, selection of 'benchmark sites', and cost-effective studies of the impacts of trypanosomiasis in them."
Published November 1998