CHAPTER 4
WORK OS CONSERVATION OP ANIMAL GENETIC
RESOURCES BY THE INTERNATIONAL LIVESTOCK CENTRE FOR AFRICA (ILCA)

by

J. C. M. Trail

(ILCA, P.O. Box 46847, Nairobi, Kenya)

Summary

There are two broad relevant areas within which ILCA has been working, studies on trypanotolerant livestock in West and Central Africa and evaluation of the potential of the Sahiwal breed to contribute to milk and beef production programmes in Africa. The basic aims of a joint ILCA/FAo/UNEP study on trypanotolerant livestock were to survey their present status, appraise existing information on their productivity, and present comparisons between trypanotolerant and non-trypanotolerant livestock maintained under comparable conditions. The final report of the joint study is now completed. It is entitled "Trypanotolerant Livestock in West and Central Africa" and is produced in two volumes, one of general studies and one of specific country studies. The figures presented, and their comparison with data from other breeds in Africa, suggest that the productivity of trypanotolerant livestock relative to other indigenous types may be much higher than previously assumed.

The results presented of an evaluation of the Sahiwal and various crosses in five environments in Kenya indicate that the Sahiwal breed has potential to contribute to increased milk and beef production in major ecological zones of Africa when used in combination with breeds of Bos Taurus cattle that have high response capability for milk and beef production but are lacking in adaptability. The formation of composite breeds is one logical approach for achieving and maintaining the optimum contribution by appropriate breeds of Bos Indicus and Bos Taurus cattle.

4.1 Introduction

As a byproduct of studies of animal production systems in the different ecological zones of Africa, ILCA has built up evidence for use in planning the involvement of specific breed types in development situations. Taking as an example performance traits of cattle in Africa south of the Sahara, there appears at first sight to be a considerable body of information available. A recent tentative bibliography (1) showed over 5OO relevant original reports to have been produced during the 30 year period 1949-78. However analysis of this bibliography show that only about 20% of the references contain information on three or more performance characters sufficient to allow characterization of breed types through a productivity index, or provide comparative information on two or more breed types. Only 5% of the items provide sufficient data to allow breed comparisons on the basis of a productivity index. Thus additional objective work is necessary.

There are two broad relevant areas within which ILCA has been working, studies on trypanotolerant livestock in West and Central Africa, and evaluation of the potential of the Sahiwal breed to contribute to milk and beef production programmes in Africa.

Footnote:

1. Trail, J.CM, 1980. Merits and demerits of importing exotic cattle compared with improvement of local breeds: Cattle in Africa south of the Sahara. Intensive animal production in developing countries. British Society of Animal Production. Harrowgate.

4.1.1 The use and potential of trypanotolerant livestock

I would like to sketch for you the descriptive and production situation concerning the trypanotolerant livestock that exist at present in West and Central Africa, based on a survey that has been carried out by ILGA, FAO and UNEP working together. The final report is produced in 2 volumes, in French and English. I would also like to mention the recommendations made on further work required on the evaulation and utilization of trypano­tolerant livestock and update you on the steps being taken to interest donor agencies in this work and try to persuade them to fund parts of it.

The background to the study is that over the past decade, considerable interest has developed concerning the economic possibilities of trypanotolerant livestock in West and Central Africa.

This was given practical form by the introduction of hutnpless taurine cattle into parts of Central Africa where tsetse had prevented the entry of Zebu and Sanga from surrounding areas. Trypanotolerant cattle from West Africa were first imported into Zaire at the beginning of the century and much more recently into CAR, Gabon and Congo. In all these countries they have flourished and opened new possibilities, not only for commercial beef production in tsetse areas but also for the small scale farmer.

At the beginning of 1977 it was apparent that first-hand accounts of the status, and records of the productivity of trypanotolerant cattle, were difficult to come by. Most of the reports to a large number of meetings held in the 70's referred back to a very few older authorities. These meetings indicated that, notwithstanding the success story in Central Africa, the smaller trypanotolerant cattle in West Africa were under pressure from the larger types and these in turn were under pressure from the Zebu. As a result the Dwarf West African Shorthorn appeared to be nearly extinct in several countries and rapidly declining in others. Many opinions existed on just how productive were trypanotolerant livestock', it was often stated that they must be relatively unproductive, presumably because of their small size compared with other non-tolerant breeds.

In January 1977 the International Livestock Centre for Africa began planning a study on the use and potential of trypanotolerant livestock. At that time, FAO and UNEP were also planning a survey of the trypanotolerant cattle breeds of West Africa. To avoid duplication, the three organizations set up a joint operation.

The basic aims of this joint study were to survey the status of the trypanotolerant livestock of West and Central Africa, appraise existing information on their productivity, and present comparisons between trypanotolerant and non-trypanotolerant livestock maintained under comparable conditions. This would allow plans to be prepared: for the conservation of trypanotolerant cattle breeds which were in danger of absorption or extinction; for the most effective use of trypanotolerant breeds and crosses in livestock development schemes in the humid and semi-humid tropics; and for further research on trypanotolerant animals and on trypanotolerance. If operations along any of these lines were clearly shown to be warranted, then the study would form the basis of attempts to persuade donor agencies to provide funds for either conservation, further research, increased utilization, or combinations of these.

Eighteen West and Central African countries were included in this study. These were the coastal countries from Senegal to Zaire, plus three landlocked countries, Mali, Upper Volta and Central African Republic Parts of some of these countries are either outside the tsetse belt, or are practically tsetse free from an animal breeding point of view, so the study in fact covered part of Senegal, the Gambia, Guinea Bissau, Guinea, Sierra Leone, Liberia, part of Mali and Upper Volta, Ivory Coast, Ghana, Togo, Benin, part of Nigeria, Cameroon, Central African Republic, Gabon, Congo and part of Zaire.

The report covers the environmental backgrounds, the classification, populations, distribution, descriptions, performances, etc. of, trypanotolerant livestock throughout the area of West and Central Africa studied. Research, multiplication and development oentres and the activities being undertaken are identified and classified. Whenever possible suitable indices of productivity are developed and presented in detail for the main cattle groups, in less detail for sheep and goats. Preliminary comparisons are carried out between groups wherever possible.

I want to concentrate on the productivity picture that emerged from the data found, and then, mention the conclusions reached on further necessary work, and the steps being taken to try and bring about implementation of this further work. There are many weaknesses in the report because of lack of data and I will mention these as I go along.

Before going into the productivity picture, I will just mention that the study involved much preparatory work on collection of published and unpublished information, production of checklists for country visits and then an average of 17 days spent by a scientist in each of the 18 countries updating information and filling in gaps on information. Time spent in a country ranged from 4-5 days for countries such as Liberia with a small trypano­tolerant livestock population to perhaps 50 - 60 days for countries such as Nigeria. Country visits were mainly carried out by 4 people, Phillipe Lhoste from Bouaké, Ivory Coast employed for one year from IEMVT as a joint FAO/lLCA consultant, Christian Hoste, Yves Wissocq and Ingeborg Reh of ILCA, with some assistance from Ian Mason. The study area covers 4.7 million km² (60% of total of 18 countries) and about 8 m trypanotolerant cattle; 11.5 m trypanotolerant sheep; 15 m trypanotolerant goats. Also 6 m Zebu. Cattle can be basically grouped into N'Dama, West Afrioan Shorthorn and Zebu x both. The N'Dama with 3^1/2 m head is numerically the most important cattle breed. The WAS has about 2 million head represented by many breeds, for example the Muturu in Nigeria. Baoulé in Upper Volta and Ivory Coast, Somba in Benin and Togo, ete. (only o.1 m being the dwarf type) and the 2^1/2 million cross-breds with Zebu seem to be increasing, usually deliverate with * zebu introduced, the motivation being larger draught animals, more meat, more milk per animal.

The sheep type recognized as trypanotolerant is the small West African sheep Djallonké found over the whole of West Africa, and is the only breed represented in the Coastal areas. Similarly the dwarf goat, also called West African dwarf: or Djallonké corresponds closely in name, size and distribution to the dwarf sheep.

Turning to the productivity aspect, in each detailed country section, whenever sufficient information has been available, estimates of the main production traits required to build up a productivity index has been given and the very rough environmental and management situations under which these basic productivity data have been achieved, have been indicated. In the case of cattle, the traits evaluated are reproductive performance, cow and calf viability, milk production, growth, and cow body weight.

These have then been used to build up the index of the total weight of calf and live-weight equivalent of milk produced, firstly per cow per year and finally per 100 kg of cow maintained per year. With the level of data available, this final index is the most meaning­ful method of comparing the actual productivities of the wide range of cattle types involved. Its merit lies in relating all the more important production traits back to the actual weight of breeding cow that has to be supported, this being closely connected with maintenance costs. The traits and production indices values have been derived for two basic management systems, village and ranch or station and for four tsetse challenge levels very arbitrarily designated zero, low, medium and high by discussion with the experienced people on the ground, but very very subjective. In the case of trypanotolerant smallstock, production information on individual traits is scarce, but similar production indices have been built up wherever possible.

The syntheses and comparisons of the cattle data from the individual reports are approached through a number of steps. First the 30 situations where productivities of the two main trypanotolerant groups. N'Dama and West African Shorthorn, are available are combined to compare the two groups and get an indication of the effects of management systems and level of tsetse challenge although these of course can he confounded with other environmental factors, but we are trying to get indications. (The 30 situations are those where our field scientists really believed the data to be good). A shortcoming of course is the number of situations where only small pieces of productivity data in isolation were available, not enough to allow any kind of index to be constructed.

On the basis of the index of total weight of one-year-old calf and liveweight equivalent of milk produced per 100 kg of cow maintained per year, no significant differences have been found between the two main trypanotolerant cattle groups, the N'Dama and the WAS, the mean value being 28.5 kg. The influence of management system and level of tsetse challenge is rather clearly shown, there being a 30% lower productivity under village compared with ranch or station, and 27% and 53% less for medium and high challenge respectively, compared with low. So this gives some indications of management level and challenge level effects, but there is not nearly enough information to look at interactions between these.

Next are considered the few situations where the productivity of crosses between Zebu and humpless cattle are available, (medium challenge, crosses not as good). Third are examined the equally few situations where productivity figures on Zebu cattle in this area have been obtained, zero, light, medium - no significant difference. The comparison is then expanded to cover Zebu in tsetse-free areas of the study zone countries, and finally other tsetse-free areas of Africa.

These comparisons with information on production traits of indigenous cattle maintained in tsetse-free' areas of Agrica outside the study zone indicate that for trypanotolerant cattle under light tsetse challenge the productivity per unit weight of cow maintained is only approximately 4% less than that of a wide range of other indigenous Zebu and Sanga types in non-tsetse challenge areas throughout Africa.

In the case of sheep and goats, all I want to comment is that there is no evidence to suggest that trypanotolerant sheep and goats have lower levels of productivity than the sheep and goats in other situations evaluated throughout Africa.

The conclusions are that the experiences described in the country studies show that it is biologically possible to maintain trypanotolerant cattle, sheep and goats, in infected areas and to establish cattle in areas where they have not previously been bred. The productivity figures presented, and their comparison with data from other breeds in Africa, suggest first that the productivity of trypanotolerant livestock relative to other indigenous types may be much higher than previously assumed; second that in certain circumstances plans for increased utilization of trypanotolerant breeds may well be immediately justified; and third that more accurate evaluation of productivity in relation to degree of trypano-somiasis can be a field of major importance.

In order to obtain suggestions for technical studies to allow convincing recommendations to be made for utilization, ILCA brought together a number of consultants to spend time with the scientists who had made the country visits and then arranged discussions with representatives from other organizations working in this field ILRAD, IBAR, FAO etc. They concluded that it was clearly essential to have comparative data on the biological and economic productivity of trypanotolerant and other breeds under variety of trypanosome challenges, management systems and other environmental influences. Critical comparisons of the productivity of different classes of livestock for example trypanotolerant cross-breds and susceptible exposed to various degrees of tsetse challenge properly evaluated under both village and ranching or station management in different geographical locations (to account for variations in the nutritional, climatic and parasitic environments) would be ideal. Once the interactions with challenge level, management systems and other environ­mental variables had been assessed, the breed differences could be evaluated.

It would only be possible in practice to obtain information on different breeds and their interactions with levels of tsetse challenge, management systems and environments in a piece­meal fashion from various centres and countries. Depending on the number of environments which were sampled, the measurements of productivity and tryanotolerance would take three to five years. The information collected would include a full description of the management system, productivity data, economic data, trypanosomiasis and other disease status and degree of trypanotolerance. These measurements would make it possible to establish and interpret the interrelations between productivity and trypanosome infection under the various circumstances. It was though that substantial progress could be made by maximum utilization over a 3 to 5 year period of the information potential from a selection of locations identified in the country visits of the study. This involves the establishment of a network of stations encompassing breed x management x disease challenge situations.

In the 18 countries, preliminary enquiries were made with Government stations and institutions, universities, commercial ranches, village groups, etc. with suitable facilities and programme intentions, concerning their possible willingness to cooperate in further work on the use and potential of trypanotolerant livestock. Many localities are identified in the report where relevant work is in progress, but in nearly all cases an additional input is needed over at least 3 years before they can yield conclusive results.

The reasons for interactions found under field conditions may be impossible to interpret unless some of the possible causes have been investigated under controlled experimental conditions. This information the report suggests might be obtained by providing funds for university, government research institutes, etc. in Africa. There is a training component to this approach, since a number of these studies could be carried out as part of post­graduate work. The main focus of studies would be comparative investigations, possible lines of research would cover: factors affecting the interaction of breeds and levels of challenge (nutrition, physiological status, work load for oxen and other stresses). Relationship between production potential and trypanotolerance: Production response of trypanotolerant breeds to chemotherapy: Simultaneously, whenever possible research on genetic applications would automatically be carried out: (selection in tolerant breeds for rate of gain mature size with identification of correlated responses in terms of tolerance; estimation of heritability for possible measurements of tolerance and whenever possible, estimation of tolerance among breeds, their crossbred offspring and further descendants to discover hereditary patterns).

4.1.2 Steps taken in establishment of a network of trypanotolerant livestock herds.

The decision to support such work with a limited amount of core funding was taken by ILCA, after the proposal was presented to its programme committee last year. ILCA's main interest for the future is to help coordinate research and project work already in progress in order to ensure a flow of reliable data on the biological and economic productivity of different breeds under different environmental conditions and levels of trypanosomiasis challenge. The approach that is being adopted is to identify selected sites, where work is in progress and where more definitive data can be collected for relatively little additional input. Most of the likely sites represent projects funded and assisted from international or bilateral sources, and the first concern, therefore, was to see whether the donors involved were willing to support the concept of a research network by contributing additional funds or technical assistance to the sites as required. This was a necessity if a network was to be established based on existing operations, as opposed to a network of new activities.

A copy of the draft report was sent in early 1979 to the international, multilateral and bilateral agencies involved in development projects in this zone of West and Central Africa. Accompanying the report was a short paper indicating the possible value of further work with trypanotolerant livestock, and a brief list of possible situations where each of the agencies was already operating. A meeting was then arranged by ILGA in FAO Headquarters Rome at the end of May 1979 attended by representatives of Prance, Belgium, UK, EEC, IBRD, FAO, etc. Possible sites were discussed in turn and there was strong support in principle from virtually all agencies.

The discussions stressed that in certain cases requests to donor agencies must come from the countries themselves. Thus the immediate requirement was to arrange for technical discussions in the field covering a number of promising situations. It was decided that ILCA would write directly to the Ministries of Agriculture of countries concerned explaining the intention to establish a network, the advantages for the host country and the desire to have meetings as soon as possible in each proposed field situation.

This was immediately done for possible situations in Senegal, Ivory Coast, Gabon, Congo and Zaire. The reaction from these oountries was very enthusiastic and field visits were planned to produce detailed proposals for the donor agency concerned. In these field discussions, it was stressed that there are three areas within which each site must be capable of building up information simultaneously: animal productivity, both biological and economic; animal health, especially trypanosomiasis and helminthiasis; and tsetse challenge. Considerable progress has now been made concerning two major situations in Zaire, in cooper­ation with the Government of Belgium.

On the conservation side, the Dwarf West African Shorthorn, with a total population of only 0.1 million, is the only type in a precarious situation and the report makes suggestions on conservation measures combined with improved utilization and further evaluation.

4.13 Evaluation of the potential of the Sahiwal breed to contribute to milk and beef production programmes in Africa.

A second area of work for ILCA has been an evaluation of the potential contribution of the Sahiwal breed to milk and beef production in Africa. Kenya is the only country in Africa with major Sahiwal resources and serves as an important source of stock and semen for the whole continent. Considerable information on the productivities of pure Sahiwals has come from the Kenya National Sahiwal Stud. However very little production information has hitherto been available on Sahiwal crossbreds under commercial management.

Purebred Sahiwal (exotic Bos indicus), Sahiwal crosses with breeds of Bos Taurus cattle in different percentages and combinations, pure Bos taurus exotic (Ayrshire) and two breeds of indigenous Bos indicus cattle (Boran and Bast African Zebu) were examined in five environments in Kenya that varied in elevation from sea level to 2200 meters and in mean annual precipitation from 610 mm to 1043 millimeters. The production units varied consider­ably in production potential, production goals and objectives in regard to emphasis on milk production relative to beef production, (see Table 4.1)

Table 4.1 Site descriptions

The production objectives of the five herds varied from essentially beef only in one herd to a herd where milk production was the primary objective with all calves removed from their dams and pail fed shortly after birth; beef production was relegated to a secondary objective in this herd. Thus, the production units that provided data varied considerably in production potential, as determined by the climatic environment with corresponding variation in production goals and of objectives in regard to emphasis on milk production relative to beef production.

The environments of the five herds were ranked on overall productivity levels achieved by the breeding groups of cattle utilized in their respective programmes; production potentials ranged from 60% to 144% as a percentage of the mean productivity of the five units. Seasonal effects influenced production characters to varying degrees; for the mean of all units, seasonal effects had greatest influence on milk production, growth rate, viability and reproductive characters in the order listed. Seasonal influences were great­est, on all characters, in the herds where the degree of modification of the natural environment was minimal. Level of precipitation during specific periods of the production cycle had a major effect on milk production and on growth rate; however, the effects of level of seasonal rainfall on viability and reproduction characters were not of major importance.

In two of the higher potential units that contributed data to this study, crosses of the Sahiwal breed with breeds of Bos taurus cattle markedly superior to the purebred Sahiwal breed for characters relating to milk production as well as an index of cow productivity. In what should be the highest potential site among the five units from the standpoint of climatic and nutritive environment the Ayrshire-Sahiwal cross cows exceeded the straightbred Ayrshire cows by 3.8% in productivity index per cow per year in spite of the preferential treatment in nutritive environment that was provided to the straightbred Ayrshire cows. The straightbred Ayrshire cows produced 185 kg more milk per lactation than the Ayrshire-Sahiwal cross cows but the higher calving percentage and greater calf survival rate of the Ayrshire-Sahiwal cross cows than the straightbred Ayrshire cows acoounted for their higher index of cow productivity.

For the three highest potential units that contributed data to this study where the milk production objective had higher priority than the beef production objective, both milk production and cow productivity index were reduced when the Sahiwal breed contributed more than 50% of the germ plasm to a population where the remainder was contributed by the Ayrshire breed. In the herd that provided the highest nutritive environment and had the highest level of milk production the breeding group that was approximately 67% Ayrshire -33% Sahiwal was superior in most milk production related characters including cow product­ivity index to the breeding group that was 33% Ayrshire - 67% Sahiwal, even though this herd is located in the most stressful climatic environment; sea level 3.5° latitude south. Thus, it is concluded that the Ayrshire breed excels the Sahiwal breed in transmitted effects for milk production.

On the basis of these results it is indicated that the most optimum percentage contribution by the Sahiwal breed for the three highest potential units in this study, is the range of from 25% to 50% with the remainder contributed by breeds of Bos taurus cattle. This interpretation is based on results from sites representing the humid part of the semi-arid to humid ecological zone, the lower potential parts of the temperate highlands ecolog­ical zone and the lower to mid potential parts of the temperate highlands ecological zone.

When straightbred Sahiwals were compared with the indigenous Boran (Bos indicus) breed in a beef production environment representative of the higher potential parts of the arid to semi-arid ecological zone, the differences between the two breeds were small for most characters evaluated. On fitness related characters, the Sahiwal breed proved well adapted to the environment. The Sahiwal breed excels the Boran breed in maternal ability, whereas, the Boran breed excels the Sahiwal breed in transmitted effects for growth. When credited with milk extracted for domestic use, the Sahiwal breed was superior to the Boran breed in cow productivity index. It is concluded that the Sahiwal breed has potential to make a contribution to programmes in the higher potential parts of the arid to semi-arid ecological zone where the production objective is primarily beef. The greatest potential contribution for this use in this ecological zone is either through organized crossbreeding systems to use heterosis or as a contributor to composite breeds. Results showed the Sahiwal breed to be superior to the Ayrshire breed in transmitted effects for growth rate, indicating that the Sahiwal breed has potential for use in programmes that have a beef production objective.

The Sahiwal breed was compared with the indigenous Small Bast African Zebu breed in on unit which represents the higher potential parts of the arid to semi-arid ecological zone. Results show the Sahiwal breed to greatly excel the indigenous Small East African Zebu breed in milk production related characters and in growth related characters, further, the Sahiwal breed had a 38 day shorter calving interval which indicates a high level of adaptability to the relatively harsh nutritional environment under which these evaluations were conducted.

The results from the five herds representing one major ecological zone and parts of two additional ecological zones involving a range of production objectives indicate that the Sahiwal breed has potential to contribute to increased milk and beef production through its high level of adaptability to the natural environments of these major ecological zones of Africa modified to the degree most favoured by technological and economic feasibility when the Sahiwal breed is used in combination with breeds of Bos taurus cattle that have high response capability for milk and beef production but are lacking in adaptability to the natural enbironments of these ecological zones. The Sahiwal breed is considered unequaled in transmitted effects for milk production among Bos indicus breeds of cattle.

Although the data available for obtaining reliable estimates of heterosis in this study were limited, the appropriate estimates are in general agreement with prior reports and the importance of heterosis on both milk and beef production characters is well documented, particularly involving crosses of breeds of Bos taurus cattle with breeds of Bos indicus cattle. Thus, a breeding system to utilize heterosis is strongly suggested.

The results from the three units that have included crosses of the Sahiwal breed with the Ayrshire breed in different proportions indicate that there is an optimum percentage contribution by the Sahiwal breed to populations where the remainder is contributed by the Ayrshire breed and that this optimum contribution cannot be achieved and maintained by a breed rotation crossbreeding system because of the wide fluctuation between generations of between 67% and 33% in genes contributed by the breed of the sire and by the breed of the maternal grand-sire in a two-breed rotation crossbreeding system. Further, on a global basis a high percentage of the cattle are represented by herds that are of sub-optimal size to use organized crossbreeding systems on a self-contained basis.

The formation of composite breeds is a logical approach for achieving and maintaining the most optimum contribution by the most appropriate breeds of Bos indicus and Bos taurus cattle with selection of contributing breeds based on comprehensive characterization of candidate breeds in the climatic and nutritive environments that are consistent with the production situation.

In addition to forming composite breeds to achieve and maintain the most optimum contribution by highly selected breeds to result in the most optimum additive genetic composition for the production situation, composite breed formation should also have the objective of utilizing heterosis. Retention of initial heterozygosity after crossing and subsequent random mating with the crosses (inter se) is proportional to 1 -ⁿp², where P₁ is the fraction of each of n breeds contributing to the pedigree of a composite breed. Thus, retention of heterozygosity favours including an optimum number of breeds, balancing the increased heterosis retention as a result of including additional breeds against possiti loss of average additive genetic merit resulting from a decrease in selection opportunity between breeds as a result of including more breeds as contributors to a composite breed. An important consideration in the formation of composite breeds is to maintain effective population size sufficiently large so that initial advantage of increased heterozygosity is not dissipated by early re-inbreeding in composite breeds.

Using information on breeds of Bos taurus cattle provided by three herds representing one ecological zone and parts of an additional ecologioal zone of Africa south of the Sahara, suggestions are presented for specific composite breeds for environmental situations represented by each of the herds from which data were analyzed. The Sahiwal breed was selected to contribute germ plasm, varying from 25% to 75%, 75%, for each of the composite breeds suggested because there are strong indications that the optimum percentage contribution by a Bos indicus breed of cattle is not likely to be less than 25% for any of the environmental situations represented by the five herds.

Travaux du Centre international pour l'élevage en Afrique (CIPBA)
en matière de conservation des ressources génétiques animales
Résumé

Les travaux du GIPEA portent notamment sur le bétail trypanotolérant d'Afrique occidentale et centrale, et sur la contribution potentielle de la race bovine Sahiwal aux programmes de production de viande et de lait en Afrique.

1. Utilisation et potentiel du betail trypanotolerant. On s'interesse depuis une dizaine d'années au potentiel économique des bovins sans bosse d'Afrique, considéréd jusque là comme un relique historique et leur trypanotolérance, comme une singularité biologique. Dans les années 1970 plusieurs réunions internationales sur la trypanosomiase ont envisagé l'elevage du bétail trypanotolérant comme la meilleure solution pour la savanne humide et les galeries forestières d'Afrique occidentale. Malgré une profusion de réunions entre 1972 et 1976, on manque de renseignements de première main sur la productivité du betail trypano­tolérant (notamment de données comparatives). En Janvier 1977 le Centre international pour l' élevage en Afrique (CIPEA) a entrepris une étude sur 1'utilisation et le potentiel du bétail trypanotolérant. A la même date, la FAO et le PNUE prèparaient une enquête sur les races bovines trypanotolerantes d'Afrique occidentale. Pour éviter le chevauchement des efforts, les trois organisations se sont réunies à Rome en mars 1977 pour organiser une étude conjointe.

Cette dernière avait principalement pour but de faire le point de la situation actuelle du bétail trypanotolérant en Afrique occidentale et centrale, d'analyser les renseignements disponibles sur sa productivité et de comparer le bétail trypanotolérant et le bétail non-trypanotolerant élevés dans des conditions semblables. Cela permettra de prendre des mesures pour conserver les races bovines trypanotolérantes qui sont menacées d 'absorption ou d'ex-tinction, de mieux utiliser les races et les métis trypanotolérants dans les programmes de developpement de l'elevage en zones tropicales humides et semi-humides et d'approfondir les recherches sur les animaux trypanotolérants et la trypanotolérance.

La version provisoire du rapport final qui rend compte de cette étude est prête. Intitule "Le bétail trypanotolérant d'Afrique occidentale et centrale" ce rapport comprend deux volumes, l' un consacré à des etudes générales et l'autre à des études par pays. Les etudes générales portent sur 1'environnement du bétail trypanotolérant dans toute la zone étudiée, ainsi que sur sa classification, ses effectifs, sa répartition, ses caractéristiques, ses performances, etc. Les centres de recherche et de développement et les activités qu'ils entreprennent sont identifiés et classés. Des indices de productivité, calculés comme étant le rapport entre le poids des descendants d'un an additionné de l' équivalent en poids vif du lait produit et le poids des reproductrices élevees pendant l'année, sont établis et présentéd en detail pour les principaux groupes de bovins et moins en détail pour les ovins et les caprins. Dans la mesure du possible, des comparaisons préliminaires sont faites entre les groupes.

Les expériences décrites dans les études par pays montrent qu'il est biologiquement possible d' élever des bovins, des ovins et des caprins trypanotolérants en zone infectée et de les introduire dans des régions où. l'on n'a jamais pratique l' élevage. Les indices de productivité, et leur comparaison avec ceux qui se rapportent aux autres races africaines indiquent premièrement que la productivité des bovins trypanotolérants par rapport a celle d'autre types indigènes pourrait bien être très supérieure à ce que l'on croyait; deuxième-ment, que dans certains cas, il serait probablement justifié de commencer dès maintenant à. utiliser davantage les bovins trypanotolérants; et troisièmement qu'il serait sans doute très intéressant d' évaluer plus precisément le rapport entre la productivité et le degré de trypanosomiase. D'après ces études, la productivité des ovins et des caprins trypanotolérants pourrait être au moins aussi grande que celle de toute un série d' autres types indigènes des zones d'Afrique exemptes de tse-tsé. II serait done tout a fait justifié d' evaluer avec plus de précision leur productivité et de les utiliser davantage.

Pour des évaluations ultérieures, il est recommandé de comparer la productivité biologique et économique des races trypanotolérantes avec celle des autres races dans des environnements où le degré d'exposition à la raaladie varie et dans des systèmes de production différents, car e'est la seule manière d'obtenir une évaluation valable de la trypanotolérance. On ne pourra faire des progrès substantiels que si, pendant 3 à 5 ans, on utilise au maximum les informations potentiellement disponibles dans une série d'emplacements reperés pendant les visites dans les pays. II faudrait pour cela créer un réseau de stations où seront réprésentés diverses combinaisons de races - conditions d'exploitation - degré d'exposition à la maladie. Dans les 18 pays considérés, pour trouver des interlocuteurs susceptibles de participer à des études ulterieures sur 1'utilisation du bétail trypanotolérant, on a effectué des enquêtes préliminaires auprès de stations et d' institutions gouvernementales, d'universités, de ranchs commerciaux et de groupements villageois disposant de moyens suffisants et prêts à entreprendre des programmes. Dans bien des endroits des travaux intéressants sont en cours mais un apport extérieur se revèle presque toujours nécessaire, pendant au moins deux ans, avant de pouvoir obtenir des résultats concluants. Un travail de préparation considerable a été effectué en ce qui concerne les premières stations qui feront partie du réseau.

2. Evaluation de la contribution potentielle de la race bovine Sahiwal aux programmes de production de lait et de viande en Afrique.Des races pures Sahiwal (Bos indicus exotique), des métis de Sahiwal et de Bos taurus croisés selon des proportions et des combinaisons diverses, des Bos taurus exotiques purs (Ayrshire) et deux races indigènes de Bos indicus (les Borans et les zébus d'Afrique orientale) ont été etudiés au Kenya dans 5 environnements differents dont l'altitude variait entre le niveau de la iner et 2 200 m et les précipitations annuelles moyennes entre 610 et 1 043 mm. Les unités de production variaient considerablement entre ce qui conceme les potentiels de production et les objectifs poursuivis selon l'im­portance relative accordés a la production de lait et à. la production de viande. Les milieux où vivaient les 5 troupeaux étudiés ont été classes en fonction de la productivité globale des groupe de bovins reproducteurs utilises dans les programmes correspondants; les potentiels de production variaient entre 64 et 145 pour cent de la productivité moyenne des 5 troupeaux. L' étude avait essentiellement pour but d' évaluer, dans les zones ecologiques concernées l'intérét potentiel, du point de vue de la production de lait et de viande de la race Sahiwal pour introduire des gènes de Bos indicus dans des populations de bovins qui avaient également recu des apports génétiques de certaines races de Bos taurus. Les zones ecologiques d'Afrique representées par les 5 troupeaux n'offrent pas, du point de vue du climat et du régime ali-mentaire, un environnement favorable aux races de Bos taurus qui ont un fort potentiel de pro­duction de lait et de viande; par ailleurs il n'est ni rentable ni techniquement possible de modifier le milieu naturel de ces zones pour 1'adapter à ces races a gros rendements. Dans cette étude on cherche done à voir comment on pourrait combiner l'adaptabilité au climat et aux conditions d'alimentation des Bos indicus (représentés par les Sahiwal) avec la forte production des races de Bos taurus qui ne sont pas adaptées à ces conditions de milieu. Le but recherche est d'obtenir et de maintenir une composition génétique additive optimale avec une capacité de réponse maximale à 1'environnement naturel modifié dans la mesure du possible etant donné les contraintes économiques et technologiques.

D'après cette etude la race Sahiwal peut contribuer à accroitre la production de lait et de viande grâce à sa bonne adaptabilité au milieu naturel de ces grandes zones écologiques d'Afrique quand elle est croisée avec des races de Bos taurus qui ont une bonne réponse, du point de vue de la production de lait et de viande, mais qui s'adaptent mal. II est logique de chercher à créer des "races synthetiques" afin d'obtenir et de conserver la contribution génétique optimum qui peut être fournie par les races Bos indicus et Bos taurus les plus appropriées; pour le choix de ces dernières on étudiera parmi toutes les races candidates celles répondant le mieux aux besoins de production étant données les conditions climatiques et nutritionnelles. Des suggestions sont faites en vue de la creation de "races synthétiques" spécifiques pour les milieux représentés par chacun des troupeaux étudiés. On a décidé que la race Sahiwal participerait de 25 à. 75 pour cent au patrimoine gànàtique des "races syn­thetiques" envisagàes le pourcentage optimum n'étant vraisemblablement jamais inférieur à 25 pour cent en ce qui concerne les environnements représentés par les 5 troupeaux. En indiquant les races pures à utiliser pour la formation des "races synthetiques" on a présumé que la race Sahiwal etait, des races Bos indicus disponibles celles qui avait le meilleur potentiel de production laitière.

Trabajos realizados sobre la conservaci6n de recursos genéticos animales por el Gentro Internacional de Ganaderia de Africa (ILGA)
Resumen

El ILCA ha estado trabajando en dos cuestiones importantes: el ganado tripanotolerante en el Africa occidental y central y el potencial de la raza Sahiwal para desarrollar programas de producción de leche y carne en Africa.

1. Empleo y potencial. del ganado tripanotolerante. Durante los últimos diez años se ha tratado de cambiar la idea de considerar al ganado sin joroba de Africa como una reliquia histórica, y su tripanotolerancia como una rareza biol6gica y se ha empezado a tener en cuenta sus posibilidades económicas. En varias reuniones internacionales sobre tripanosomiasis celebradas en los anos setenta se consideró que la cria de ganado tripanotolerante era la mejor politica a seguir en las zonas húmedas de sabana y los bosques del Africa occidental. A pesar de las numerosas reuniones celebradas entre 1972 y 1976 resulta difícil obtener información de primera mano sobre la situacifión y los registros de la productividad (especial-mente la productividad comparada) del ganado tripanotolerante. El Centro Internacional de Ganadería de Africa (ILCA) empez6 en enero de 1977 a preparar un estudio sobre el aprovecha-miento y el potencial del ganado tripanotolerante. Al mismo tiempo la FAO y el PNUMA estaban preparando también una encuesta sobre las razas de ganado tripanotolerante del Africa occidental. Para evitar la duplicación de esfuerzos, las tres organizaciones se reunieron en Roma en marzo de 1977 a- fin de coordinar sus actividades.

Los objetivos fundamentales de este estudio conjunto eran examinar la situaci6n actual del ganado tripanotolerante en el Africa occidental y central, evaluar la información existente sobre su productividad y establecer comparaciones entre el ganado tripanotolerante y el no tripanotolerante cuando se encuentran en condiciones análogas. Esto permitirá preparar planes para la conservación de razas de ganado vacuno tripanotolerante que están en peligro de absorbción o de extinción, para el mejor aprovechamiento de razas y cruzas tripano-tolerantes en los planes de desarrollo ganadero de los trópicos húmedos y semihúmedos y para ulteriores investigaciones sobre los animales tripanotolerantes y la tripanotolerancia. El proyecto de informe definitivo sobre este estudio está terminado; lleva por título "El ganado tripanotolerante en el Africa occidental y central" y se publica en dos volúmenes, uno de estudios generales y otro de estudios monográficos por países. Los estudios generales tratan del medio ecologico que corresponde al ganado tripanotolerante, y de la clasificación, las poblaciones, la distribución, la descripcion, el rendimiento y conformación, etc. de ese ganado en toda la zona estudiada. Se localizan y clasifican los centros de investigación y desarrollo y las actividades en curso. Se elaboran y presentan en detalle los índices de productividad de los principales grupos de ganado vacuno, y en menor detalle de las ovejas y las cabras; tales indices se determinan sobre la base del peso de las crías de un año más el equivalente en peso vivo de la leche producida, por unidad de peso de la hembra de cría mantenida por ano. Cuando es posible, se efectúan comparaciones preliminares entre los grupos.

Las experiencias descritas en los estudios por países muestran que es biológicamente posible mantener ganado vacuno, ovejas y cabras tripanotolerantes en zonas infectadas e introducirlos en zonas donde antes no se criaba ganado. Las cifras de productividad pre-sentadas y su comparación con datos tornados de otras razas de Africa indican, en primer lugar, que la productividad del ganado tripanotolerante en relacion con otros tipos aut6ctonos puede ser raucho mayor de lo que se suponía; en segundo lugar, que en determinadas circunstancias son inmediatamente justificables los planes para aumentar la utilizacion del ganado tripanotolerante; y, en tercer lugar, que una evaluaci6n mas exaota de la producti­vidad en relación con el grado de tripanosomiasis puede ser un criterio de una importancia mayor. En el caso de las ovejas y cabras tripanotolerantes, los resultados indican que su productividad puede ser por lo menos tan alta como la de otros tipos autóctonos en las zonas no afectadas por la mosca tse-tse en Africa. De este modo, estaría plenamente justificada una evaluaci6n mas exacta de su productividad y una mayor utilizaci6n de estas razas.

Para futuras evaluaciones se recomienda comparar la productividad biológica y económica de las razas tripanotolerantes y de otras razas en medios ecol6gicos que presenter diversos problemas y en diferentes sistemas de producción, pues ésta es la única manera de determinar el verdadero valor de la tripanotolerancia. Se considera que tan solo pueden lograrse pro- gresos sustanciales utilizando al máximo, durante un período de tres a cinco años, la in- formaci6n que es posible obtener de una serie de lugares seleccionados durante las visitas realizadas a diferentes países- Para ello, es preciso establecer una red de estaciones en lugares donde se planteen problemas de cría, manejo y enfermedades. En los 18 países se hicieron encuestas preliminares en estaciones e instituciones estatales, universidades, ranchos comerciales, y grupos de ganaderos, con servdcios y programas adecuados, para saber si estaban dispuestos a cooperar en trabajos ulteriores relacionados con el empleo y el potencial del ganado tripanotolerante. Hay muchos lugares bien identificados donde se están realizando trabajos interesantes, pero en casi todos los casos se requieren insumos adicionale durante un período por lo menos de dos años antes de que estos trabajos puedan dar resultados concluyentes. Se nan realizado considerables progresos en lo que respecta a la planificacion de los lugares donde debe establecerse la red.

2. Evaluación del potencial que ofreoe la raza Sahiwal para contribuir a los programas de producción de leche y oarne en Africa. En cinco zonas de Kenya, cuya altura varía desde el nivel del mar hasta 2 200 m y cuyas precipitaciones anuales medias van de 610 a 1 043 mm, se examinaron la raza pura Sahiwal (Bos indious exótico), la raza Sahiwal cruzada con razas de ganado Bos taurus en proporciones y combinaciones diferentes, la raza pura exótica Bos taurus (Ayrshire) y dos razas de ganado autóctono Bos indicus (Boran y cebu del Africa oriental). Los hatos estudiados variaban considerablemente en potencial y ohjetivos en lo que respecta a la producci6n de leche comparada con la producci6n de came.

Los medios ecológicos de los cinco rebaños se clasificaron de acuerdo a los niveles generales de productividad logrados por los diversos grupos de ganado utilizados en los respectivos programas; los potenciales de producción iban del 64 al 145 Por ciento de la productividad media de los cinco hatos. Uno de los principales objetivos de este estudio era evaluar, en las zonas ecológicas estudiadas, el potencial de producción de leche y came de la raza Sahiwal como proveedora de germoplasma Bos indicus a poblaciones de ganado que también recibían germoplasma de razas Bos taurus. Las zonas ecológicas de Africa represen-tadas por los cinco rehanos no constituyen un medio climático y nutricional adecuado para obtener un alto potencial de produccion de carne y leche con razas de ganado Bos taurus de alto rendimiento; tampoco puede modificarse económica ni técnicamente el medio ambiente natural de estas zonas ecológicas hasta un nivel que permita la adaptación de estas razas de alta producción. Asi pues, en este estudio se examinaban ideas y criterios para poder combinar las características de adaptabilidad al medio climático y nutricional de razas Bos taurus que carecen de esa capacidad de adaptación. El objetivo era lograr y mantener una composición genética óptima junto con una capacidad de respuesta maxima al medio natural ya modoficado al nivel más idóneo permitido por la economía y la tecnología.

Los resultados indican que la raza Sahiwal posee un potencial capaz de contribuir a aumentar la producción de leche y carne gracias a su alto indice de adaptación a los medios naturales de estas zonas ecológicas africanas cuando se utiliza en combinación con razas de ganado Bos tauras que tienen una alta capacidad para la producción de leche y came, pero que carecen de la facilidad de adaptaci6n.

La mezcla de razas en un sisterna 1ógico para lograr y mantener la contribuci6n 6ptima de las razas más adecuadas de Bos indicus y Bos taurus seleccionándolas de acuerdo a una caracterización lógica de las mas indicadas para los medios climáticos y nutricionales que son compatibles con el tipo de producción. Se proponen determinadas mezclas de razas para medios ecológicos representados por cada uno de los rebaños de los que se tomaron y analizaron los datos. Se eligió la raza Sahiwal como proveedora de germoplasma en una proporci6n que oscila del 25 al 75 por ciento para cada una de las razas mezcladas recomendadas, porque hay claros indicios de que el porcentaje óptimo de contribución de una raza Bos indicus no es probable que sea inferior al 25 por ciento en ninguna de las zonas ecológicas representadas por los cinco rebanos estudiados. Al hacer las propuestas indicadas, sobre la contribución de una raza pura para crear una raza mezclada, se partió del supuesto de que la raza Sahiwal posee el mejor potencial para la producción de leche entre las razas Bos indicus generalmente disponibles.