2.1 Research policies on trypanotolerant livestock breeding
2.2 Research activities on the productivity of trypanotolerant breeds
2.3 Research on trypanotolerance
Research activities on trypanotolerant livestock may be classified under two main headings, depending on whether the emphasis is on studying and increasing the productivity level of these breeds or on their trypanotolerance.
Both topics are of course complementary and interactive but for clarity purposes, are treated separately. Recent developments in the research policies of the different countries are discussed in section 2.1 and the results obtained in the two areas are evaluated in section 2.2.
A review of the 19 West and central African countries would be a tedious exercise. Furthermore, some of these countries have continued to pursue the same research policies since the previous study and continue to strive for improving their livestock production systems. This report will therefore focus on the major achievements of the past 10 years.
A major activity in trypanotolerant livestock research was the establishment in the Gambia of the International Trypanotolerance Centre (ITC/CIT) which became operational in 1984.
ITC was established through the stated political will of the Gambia and with a loan from the African Development Bank (ADB) for its construction, as part of a national livestock development project. The Centre has also developed a research programme. The entomological section is funded by the UK Overseas Development Administration (ODA), the Animal Health and Production Section by the regional funds of the European Economic Community (EEC) through the International Livestock Centre for Africa (ILCA) and the International Laboratory for Research on Animal Diseases (ILRAD).
Senegal collaborates actively with ITC in this research programme from its station in Kolda, Casamance. There has also been a radical change in its livestock development policies which now encourage studies to be conducted in the village environment rather than on-station. A systems approach which appears promising has also been developed.
In view of the size of its trypanotolerant livestock population, Guinea has taken an important decision in the field of animal research and production to discontinue crossbreeding of the N'Dama breed with the exotic Red Steppe breed. At the same time, priority is being given to research activities on the N'Dama and the establishment of a national breeding programme for this breed.
On the other hand, Mali seems to be committed to pursuing its programme of crossbreeding the N'Dama breed with exotic breeds such as the Red Steppes at the Centre de recherches zootechniques de Sotuba in an effort to improve milk production in the suburban areas of the capital. The activities of the Central Veterinary Laboratory now include the planning of chemoprophylaxis strategies for the trypanocidal treatment of various livestock species and for tsetse control.
Burkina Faso continues to support the Centre for Animal Trypanosomiasis Research (CRTA) and its two components the tsetse programme and the trypanotolerant programme. Togo has, however, expressed the wish to discontinue research programs on trypanotolerance at Avetonou Livestock Production and Research Centre (ALPRC) and to focus on production of draught oxen and beef cattle.
Despite the small size of its trypanotolerant cattle, Cameroon has agreed that the Livestock Production Research Centre (LPRC) should maintain and study local trypanotolerant cattle breeds on-station. The major objective here is to conserve the genetic stock of its local breeds but this effort is noteworthy.
Central African countries are still more concerned with increasing the number of trypanotolerant livestock than with actual research on those breeds. Only Gabon and Zaire are actively conducting research on trypanotolerant livestock within the framework of the African Trypanotolerant Livestock Network. The small ruminant programme in the Congo may be included in this category because it is pursuing with applied research objectives. However, these are far from real research policies on trypanotolerant livestock.
Two detailed studies which provided substantial additional information on the productivity of trypanotolerant cattle were conducted during the study period. The first, conducted in Senegal and published by Fall et al (1982), provided additional information on the productivity of Djallonké sheep and N'Dama cattle maintained on station at Kolda. The second, conducted in Sierra Leone and published by Carew et al (1986), provided comparative results on the productivity of the N'Dama and Sahiwal breeds and crossbreeds of the two breeds raised at Teko Station. Data analysis and preparation of the reports were carried out in collaboration with the Livestock Productivity and Trypanotolerance team of ILCA.
The most important activity of the study period was the establishment of the African Trypanotolerant Livestock Network by ILCA and ILRAD and the knowledge already derived from its work.
The Network was established following a joint FAO/ILCA/UNEP study. The results of the study were published in Volumes 1 and 2 of this Monograph. The brief introduction to the Network is an extract from ILCA (1986a).
A large amount of data had been collected during visits made in 1977 and 1978 as part of the FAO/ILCA/UNEP study. The main contribution of the study is that it rehabilitated trypanotolerant livestock in showing its relatively high productivity and renewed interest in trypanotolerant livestock. Nevertheless, it was evident that more detailed data would have to be obtained on the productivity of different trypanotolerant breeds maintained in different areas and under different levels of tsetse challenge and livestock production systems.
Consequently, ILCA developed a research network to improve livestock production in tsetse-affected regions of Africa by achieving a better understanding of genetic resistance, acquired resistance, environmental factors which affect susceptibility and the effectiveness of current control measures and ensuring optimal application of both existing knowledge and recent research findings (ILCA, 1986a).
The selection of sites for the network was based on several criteria: complementarily in terms of disease level, tsetse challenge and livestock breeds; the willingness of national institutions concerned to cooperate; the availability of basic research infrastructure; and the extent to which donor agencies were prepared to provide the supplementary funds required.
The key factor determining the success of such a network, which requires the collection of very large quantities of data in fields as diverse as environment, veterinary epidemiology and livestock production parameters, is the standardisation of protocols and data-recording systems and the training of field staff in the collection of data. To this end, ILCA, in collaboration with ILRAD and the International Centre for Insect Physiology and Ecology (ICIPE) has organised training courses in English and French every year since 1982, and in 1983 published a training manual (Murray et al, 1983).
Within the Network, ILRAD is responsible for training, standardisation of protocols on livestock diseases, and evaluation of trypanosomiasis risk and ILCA is responsible for coordinating research activities at the sites selected and for collaborating with national organizations and donor agencies. ILCA is also responsible for the animal production and nutrition as well as for data-processing aspects.
By December 1986, training had been provided for 53 field staff and 11 sites had been established in 7 countries. Tsetse and animal populations for each site are presented in Table 2.1. This table illustrates clearly the very wide range of combinations between tsetse populations and livestock production systems in which data are routinely collected. Additional data were obtained by a comprehensive analysis of data from a network-associated site in Tanzania.
By the end of 1985 eight sites had already collected data covering at least the two-year period 1 January 1984 to 31 December 1985. An internal meeting of the Network was therefore convened to plan how the preliminary results for each site were to be analysed. The proceedings of that meeting was published in June 1986 (ILCA, 1986a), and a report on the first two years of the Network were published in December 1986 (ILCA, 1986b).
Since then, the Network has continued to collect data and a second meeting, held in November 1987, was attended by over 100 researchers who reviewed the progress made in their various activities. Fourteen sites in nine countries were represented. Research workers from other national and international institutions also participated in the meeting at which recognized specialists presented the state-of-the-art knowledge in their respective fields.
The meeting also evaluated all programs and planned future activities of the Network. These activities will be conducted under four major topics:
· trypanosomiasis epidemiology
· trypanotolerance
· genetics of trypanotolerance
· biological and economic evaluation of the effect of control measures on productivity.
Further information on these topics may be found under the relevant sections.
Table 2.1. Tsetse and livestock populations at Network sites.
|
Site |
Country |
Tsetse group |
Species |
Type |
Management system |
|
Kolo |
Zaire |
palpalis |
Cattle |
Trypanotolerant |
Ranch |
|
Avetonou |
Togo |
palpalis |
Cattle and sheep |
Trypanotolerant and non-trypanotolerant |
Ranch and Village |
|
Sokode |
Togo |
palpalis |
Sheep and |
Trypanotolerant |
Village |
|
Tengrela |
Côte d'Ivoire |
palpalis |
Cattle and sheep |
Trypanotolerant and non-trypanotolerant |
Village |
|
Boundiali |
Côte d'Ivoire |
palpalis |
Cattle and sheep |
Trypanotolerant and non-trypanotolerant |
Village |
|
Idiofa |
Zaire |
palpalis and fusca |
Cattle |
Trypanotolerant |
Village |
|
OGAPROV |
Gabon |
palpalis and fusca |
Cattle |
Trypanotolerant and |
Ranch |
|
Mushie |
Zaire |
fusca |
Cattle |
Trypanotolerant |
Ranch |
|
Muhaka |
Kenya |
morsitans and fusca |
Cattle |
Non-trypanotolerant |
Ranch |
|
Ghibe |
Ethiopia |
morsitans and palpalis |
Cattle |
Non-trypanotolerant |
Village |
|
ITC |
The Gambia |
morsitans and palpalis |
Cattle |
Trypanotolerant |
Village |
Source: ILCA (1987).
2.3.1 Vectorial potential of tsetse
2.3.2 Study of the parasite
2.3.3 Final host response
As was clearly stated in the introduction to this chapter, the division between research activities on productivity and those on trypanotolerance was somewhat arbitrary. For example, it is evident that data collected and analyzed by the African Trypanotolerant Livestock Network will make a significant contribution toward a better understanding of trypanotolerance.
At the same time, more basic research is being conducted by national and international laboratories on the vector-parasite-host complex which are discussed in the following section. The ultimate objective of these research activities is to strengthen the trypanotolerance of Trypanotolerant breeds and to induce it in local or exotic trypanosusceptible breeds, in order to increase the potential for livestock production in tsetse-infested areas.
Since it is impossible to cover all the aspects involved in a single institution, each laboratory or center is more or less specialized. Current research work is classified according to whether the main focus is on the vector, the parasite or the host. Although the first two are not directly concerned with trypanotolerance, they cannot be ignored when studying this phenomenon. The following review is from Hoste (1987a) and ILCA (1988a).
The vectorial potential of any given tsetse species is a function of its ability to ingest trypanosomes when feeding on an infected host, to develop an infection and to transmit infective trypanosomes to new hosts. Many factors related to the tsetse (species, sex, age, physiological conditions, feeding habits), the trypanosome involved (strain, forms, number), and the ecology (climate, host availability) can influence each of these three stages.
Research on this subject has been conducted by various African and European institutes, including the International Centre of Insect Physiology and Ecology (ICIPE) in Kenya and the Tsetse Research Laboratory (TRL) at Langford, Bristol, UK.
A review by Rogers (1985) on trypanosomiasis risk was published recently. The problem has since become even more complex. Recent research has even produced some evidence of discrepancies in tsetse resistance to trypanosome infection (Maudlin et al, 1986).
Another important area of research concerns the factors determining the tsetse-host attraction. This needs to be studied at the breed, species and individual level, since it is obvious that an increased number of bites increases the risk of infection. Research in that field is conducted mainly by ICIPE, TRL and the Tropical Development and Research Institute (TDRI) in the UK, the Tsetse and Trypanosomiasis Division of the Veterinary Services in Zimbabwe and, more recently, the tsetse control team of the Centre de recherches sur les trypanosomoses animales (CRTA) in Burkina Faso.
Researchers of the African Trypanotolerance Livestock Network are also studying the various factors which determine tsetse challenge and their relationship with trypanosome prevalence in livestock.
ILRAD has undertaken to improve the current level of knowledge of the trypanosome, its characteristics, development and ability to modify its structure, with a view to controlling multiplication of the trypanosomes. This may eventually lead to the production of a vaccine.
Trypanosome infections, particularly in trypanotolerant animals often result in low-level and sporadic parasitaemia. More reliable methods of diagnosis in the field should therefore be developed, particularly in cases where samples can only be obtained at very infrequent intervals. Such methods would contribute towards more accurate trypanosome diagnosis and research methods.
CRTA is also studying the trypanosome, mainly to monitor and compare its development within trypanotolerant and trypano-susceptible animals.
This covers two very distinct areas of research: mechanisms of trypanotolerance and characterization of the trypanotolerance trait of the most trypanotolerant cattle breeds.
Several research centres in Africa and elsewhere are currently working on the definition of trypanotolerance, on means of determining or at least evaluating it, and on possible selection criteria.
Trypanotolerance appears to be associated with at least three apparently related characteristics with independent genetic control, namely the capacity to control parasitaemia, resist the development of anaemia and develop an effective immune response (Murray, 1988).
ILRAD and CRTA conducted detailed studies on the development of chancres at bites area but no significant results were recorded (ILRAD, 1986).
Research work, notably with experimental infections by injections, has demonstrated that differences in levels of parasitaemia may be the result of innate differences in the immune response and that within the immune responses, the antibody response constitutes the most important factor. Many other factors, such as the host's ability to stimulate pleomorphism in the trypanosome or certain physiological characteristics, may also be implicated in these resistance mechanisms to trypanosoma. A comprehensive summary on the subject has been written by Murray et al (1982) and a more specific one on the immunology of the African trypanosomiasis by Roelants and Pinder (1984). The main research organisations studying this aspect of the host response are ILRAD (ILCA, 1986) and CRTA.
Various individual and external factors often interfere with the understanding of the phenomenon of trypanotolerance, making it an extremely difficult field of research, but nevertheless an interesting one. In fact, trypanotolerance can be affected by the age and sex of the animal, by maternally derived immunity, previous infections, stress factors such as poor nutrition, overwork, inter-current disease and physiological condition (weaning, parturition, lactation) and the animal's susceptibility to other diseases. It can also be affected by the intensity of the trypanosomiasis risk and the virulence of the trypanosome strain involved. Available information on the influence of all these factors on trypanotolerance was reviewed by Murray et al (1982) and more recently by Touré and Hoste (1986a).
Researchers of the African Trypanotolerant Livestock Network conducting studies on the genetics of trypanotolerance are primarily concerned with the traditional method of genetically improving resistance to diseases which could provide information directly usable in practical animal breeding applications. Results obtained so far have been promising and further research to determine heritability and genetic correlation between criteria associated with the traits described by Murray (ILCA, 1988) is being conducted.
Furthermore, disease resistance in some domestic and laboratory species has been shown to be associated with the major histocompatibility complex (MHC). An association between the MHC and trypanotolerance, and the identification of individuals having superior trypanotolerance traits through this association could pave the way for developing cost-effective and practical trypanotolerance selection programs (Teale et al, 1988).
Major research efforts are also being made to identify genetic marker systems for characterising trypanotolerant and trypano-susceptible animals. Ideally, these markers should be simple and low-cost and should be usable as criteria for selecting for trypanotolerance. Two research centres studying this aspect of trypanotolerance are based in West Africa: CRTA in Burkina Faso and the Avetonou Research and Livestock Production Centre (Centre d'Elevage d'Avetonou, Togo) (ARLPC). An ILRAD team is also studying this subject as are other institutes in Europe including the Animal Breeding Research Organisation (ABRO) in Edinburgh, Scotland, UK, the Institute of Tropical Medicine in Antwerp, Belgium and the National Agricultural Research Institute (INRA) in Jouy-en-josas, France.
Although no definitive and simple parameter has yet been found, some promising results seem to have been obtained by comparing haemotypes of trypanotolerant and trypano-susceptible livestock, such as polymorphism of serum proteins (albumin, transferin), erythrocytes (blood types, haemoglobin, nucleoside purine, phosphorylase purine, carbonic anhydrase, dehydrogenase malate) and leucocytes (major histocompatibility system, deaminase adenosine) (CRTA, 1986).
In conclusion, it should be emphasised that since the publication of Volumes 1 and 2 of this Monograph, decisive progress has been made by countries and research organizations involved.
Almost all tsetse-infested West and central African countries are aware of the importance of pure trypanotolerant breeds and the need to conduct research on these breeds. The enthusiasm shown by national research bodies to be integrated into or to participate in the African Trypanotolerance Livestock Network is ample evidence of this fact.
The establishment, during this period, of the African Trypanotolerant Livestock Network which covers or will cover 16 sites in 10 countries (ILCA, 1988b) demonstrates the dynamism of the two major international research centres, ILCA and ILRAD. The desire of the international community to participate in research activities on trypanotolerant livestock is also reflected in the funding it provided for the establishment of the International Trypanotolerance Centre (ITC/CIT).
In spite of these encouraging results, the major part of the work remains to be completed and the efforts already made should be sustained. Improved contacts between national and international research institutes during the past 10 years have resulted in increased collaboration and in certain cases joint programme planning. Donor agencies are aware of this and are now encouraging closer collaboration. The biannual meetings of the International Scientific Council for Trypanotolerant Research and Control, an institution of the Organisation of African Unity (ISCTRC/OAU) have also substantially contributed towards improving contact and collaboration among researchers.
