INTRODUCTION
The meeting was opened on 16 March by Dr. D.F.R. Bommer, Assistant Director-General, Agriculture Department, who welcomed all participants on behalf of the Director-General of the Food and Agriculture Organization of the United Nations. He referred to the progress which had been made in carrying out the recommendation of the World Food Conference (1974) that FAO should launch a long-term programme for the control of animal trypanosomiasis in Africa. However, in the moist savannah and forest gallery areas there was no immediate chance of eliminating tsetse fly by aerial spraying. In these areas, which amount to some 2 million km2, the present policy is to encourage the breeding of trypanotolerant cattle. Our knowledge of the mechanisms and genetics of trypanotolerance and the breeding of trypanotolerant animals is inadequate. Therefore this Consultation has been organized to review present knowledge, to describe work in progress and to recommend future research in the field.
When the formal session began, Dr. Touré was unanimously elected Chairman and Dr. Nuru, Vice-Chairman.
At the closing session Dr. Griffiths reported that the Director-General had expressed his deep personal interest in the trypanosomiasis control programme. He would recommend to the FAO Council when it meets in July that this programme should get the budget increase which had been requested. Dr. Griffiths thanked all participants and hoped that this would be only the first of a series of expert consultations on trypanotolerance. In fact a second was planned in two years time.
1. REVIEW OF PRESENT SITUATION AND KNOWLEDGE
1.1 Trypanotolerant Breeds of Cattle: Origin, Characteristics, Distribution
About 30 million sheep and goats and 8.4 million cattle live in West and Central Africa in the areas infested by the tsetse flies which are the vectors of trypanosomes.
The treat majority of the cattle are humpless. They may be classified into three groups according to their place of origin:
The N'Dama group coming from the mountainous area of Fouta Djallon. Most of these cattle are in Guinea, South Senegal and North-West Ivory Coast. Smaller numbers are to be found in the other countries bordering on Guinea.
The Baoulé, Somba, Muturu group occupying a vast strip of territory lying in the Ivory Coast, Ghana, Togo, Benin, Nigeria and Cameroon between 9° and 12° North latitude.
The Lagune/Dahomey group found in a 50 kim strip along the shores of the Gulf of Benin.
From their areas of origin the N'Dama and Lagune groups have been introduced into Zaire, Congo, Gabon, Ghana and nigeria and the Baculé and N'Dama into the Central African Republic.
At the edges of the distribution areas of these groups we find a population of crossbreds between Zebu and Humpless animals - the Méré of Mali, the Keteku of nigeria, the Borgou of Benin and the N'Dama-Grande and Diakoré of Senegal.
Whatever their areas of origin and distribution these breeds are quite comparable with other African breeds in their rates of reproduction and growth. A number of publications on the subject all emphasize the precarious nature of trypanotolerance which can be diminished if the management conditions, particularly of nutrition, are not right for the animals.
1.2 Trypanotolerant Cattle Husbandry
Husbandry studies have been made over a long period. In 1931 Curasson published an account of conditions in Mali which remains true today. Rearing is localized and carried on by peasant farmers. The herds are organized at village level in one or more units comprising animals belonging to several owners. The supervision of the animals is often entrusted to Fulani herdsmen.
In Senegal one finds the same custom (though here the Fulani are often the owners) in the South-West (Casamance) and the Siné-Saloum - an intermediate area where the animals are often crossbreds. SODEVA and SODEFITE are societies for agricultural improvement which are concerned with livestock husbandry.
In Cote d'Ivoire, where the cattle are primarily in the North, it is the Senoufo and the Lobi tribesmen who keep them SODEPRA is responsible for organizing the farmers. There are many Baoulés in the herds.
In Togo and Benin studies carried out by SEDES give valuable information on breeding methods.
In Mali the entire south of the country is populated by N'Damas and crossbreds. In the Yanifolila district, which has been selected as the breeding centre, we find animals on a very pure type, in a well protected environment, free from the major infectious diseases.
In Nigeria we find the muturu breed in the Northern part of the wet forest zone and the derived savannahs. The Keteku occupied the Borgou division of Kwara State and also extends into the derived savannahs of Oyo in the Western State. The N'Dama was introduced in 1946, chiefly into the government or parastatal ranches in Kwara and Western States.
In the Central African Republic trypanotolerant breeding was started in 1957 by importing Baoulés from Côte d'Ivoire and N'Damas from Zaire. This share-farming operation was very well organized at the time it was set up and has been a success.
In Zaire breeding with N'Damas and Baoulés has been developed in two ways: by share-farming amongst the peasants and on private ranches where selection has resulted in good animals (work carried out for more than 30 years by Van Lanker).
In the People's Republic of Congo the same methods have been used but operations were started later - after 1957.
1.2.1 Usefulness of these Animal
They are used by the peasants primarily for milk. Because of the low production, milk is available only at the expense of the calf. The Fula herdsman who looks after the animals often receives the milk in payment. This method is very bad for the young calves before they are weaned.
In addition, the cattle are often used for pulling carts and ploughs. In the Siné-Saloum, Senegal, the Diakoés (zebu x N'Dama) are very will fed on peanut tops (haulms). Finally, they are always used for meat< the young bulls are slaughtered between 18 and 36 months and the cows when they are worn out.
1.2.2 Breeding characteristics
These animals are precocious. The first calving always occurs in the third year and, in the case of the Baoulé, often in the second. The calving rate under natural peasant conditions is of the order of 66 percent which means two calvings every three years. The calving performance of well fed animals (at a centre, or with the Siné-Saloum peasants) is often 80 percent and sometimes more (a calf a year).
Preweaning mortality is always very high (30–50 percent of the births) especially when the amount of milk taken from the cow is excessive. The losses between 8 and 18 months can be as high as 10 percent of the survivors, due to malnutrition and to parasites. Adult mortality does not usually exceed 2 percent of the herd.
The number of animals slaughtered for meat each year amounts to 12–13 percent of the herd which is about the same percentage as that reported from the zebu herds in the sahel, except that the slaughter weights are much lower.
The economic value is considerable. These animals, sold very near to their sites of production, in regional centres or to supply village needs, reach unit prices comparable to those fetched by the zebus in their production areas, but for little more than half the weight of meat that there is on the zebus. The breeding cows also sell at high prices because of the demand from new centres being set up.
1.3 Trypanotolerant animals other than cattle
Sheep and goats are more numerous in trypanosomiasis areas of Africa than are cattle. It is well known that the dwarf sheep and goats of West Africa can live under conditions of high tsetse challenge but there has been little scientific study on them. Their fecundity is remarkable.
Recent investigations in Kenya (Allonby) have shown that exotic breeds of sheep (e.g. Karakul) and goats (e.g. Saanen x Galla cross) have a higher rate of natural infection, a more severe anaemia and a greater weight loss than the indigenous breeds (Blackheaded Somali sheep and Galla goat). This was confirmed in experimental infections. All animals were born and reared in tsetse-free areas. This innate immunity appears to be of greater importance in the trypanotolerant small stock than greater ability to develop acquired immunity. Imported and local animals were of the same haemoglobin type.
Horses. The small Logone or Kirdi pony of Chad is also trypanotolerant.
Wild ungulates are known to be resistant to trypanosomiasis and to resemble trypanotolerant cattle in frequently exhibiting parasites in the blood which may become pathogenic if the animal is subjected to nutritional or parasitic stress.
Mice. Different strains appear to have different susceptibility to trypanosome challenge. Such a situation offers an opportunity to study the genetic basis of the phenomenon.
1.4 Biological basés of trypanotolerance
1.4.1 Biological bases of trypanotolerance
It is a hereditary biological property which enables certain breeds, or certain individuals, to live normally in a naturally infected environment while carrying pathogenic trypanosomes without themselves showing any clinical signs of the disease. This tolerance is tied up with the infective environment and with the state of health of individual animals, therefore with their total environment, particularly nutritional.
As the biological properties of organisms are an expression of their genetic constitution, research into the mechanism of trypanotolerance leads to a discussion of their biological bases. By this we mean the physiological mechanisms of metabolic processes, or the molecules whose presence can be unambiguously associated with that of trypanotolerance. It is, therefore, a question of all the biological properties which can be correlated with trypanotolerance. We are accustomed to classify these biological factors into groups according to which study-techniques are used and how the subject is approached. We must recognize that everything depends upon the biosynthesis of proteins whose mechanisms are clearly related to specific genetic structures. These factors which one arbitrarily separates, but which form a whole, are, without giving an exhaustive list: immunological, physiological and nutritional, biochemical, zootechnical and genetical.
We have to note two great gaps in our knowledge - we do not know how to measure the infective power of the environment and we do not know how to measure trypanotolerance.
1.4.2 State of our knowledge of the various factors from studies to date
Immunological factors
It has been shown that there are trypanotolerant breeds.
Differenoes have been demonstrated between zebus and humpless cattle at the level of serum proteins particularly in their immunological and clinical reactions to vaccinations against rinderpest and pleuropneumonia. The history of the testing out of these vaccines demonstrates this.
The level of serum proteins is higher and there is a third component amongst the immunoglobulin of the hyper-immune trypanotolerant animals.
Their levels of betaglobulin are correspondingly higher.
Their IgM level is more constant during the development of the immune response.
Trypanotolerant cattle produce neutralizing, agglutinating, lysing and precipitating antibodies but we have not been able to demonstrate for certain their superiority, either qualitatively or quantitatively, over those of non-tolerant cattle.
Before the first infection of the trypanotolerant cattle they do not have any natural antibodies against trypanosomes.
It must be emphasized that few studies have been done on traditional serological tests and that the production of the trypanosomic antigens remains a problem. The trypanotolerant breeds seem to be able to maintain a high level of antibodies for longer than the trypanosensitive zebus can.
Physiological factors :
Hardiness in the different species seems to be closely associated with trypanotolerance.
Maintenance of trypanotolerance is associated with an abundant and balanced diet.
Biochemical factors :
The study of biochemical polymorphism of the haemoglobin has shown a very high gene frequency for haemoglobin A in the homozygous state for the four humpless trypanotolerant breeds (pure N'Dama 1.0, Muture 1.0 and 0.8, Laguna 1.0, Baoulé 0.96).
The deficiency of G6PD which has been shown to be a factor in the growth of certain trypanosomes in vitro cannot be implicated except in the case of cattle. Where there is a biochemical polymorphism for that enzyme, but not in the horse, where it is always present, or in the small ruminants, where it is always absent.
In the rat, the level of blood calcium seems to be associated with an ability to permit the multiplication of trypanosomes.
Zootechnical and genetic factors :
Trypanotolerance seems to be particularly developed in certain humpless cattle. It seems, however, that, in some individual cases, it must also be present in zebus.
The animals of the trypanotolerant breeds are always of small size.
When trypanotolerant, humpless cattle are crossed with zebus, the trypanotolerance of their offspring is intermediate between that of their parents. The number of positive blood smears from animals in the infected environment is also intermediate.
1.5 Epizootiology and pathology of trypanosomiasis in trypanotolerant animals
1.5.1 Epizootiology
It must be recognized that most of the available data concerning the epizootiology of trypanosomiasis in the trypanotolerant cattle of the different regions of Africa are not very recent. Amongst the authors who have studied the epizootiology of these cattle, one would pick out : Chandler (1952–1958); Desowitz (1959); Stephen (1966); Ferguson (1967). More recently Roberts and Gray (1971, 1973) and Touré (1968–75) have published observations on the epizootiology of the Muturu and N'Dama, or of the N'Dama alone, in the regions where they have worked - Nigeria in the one case, Senegal in the other. In general, the principal species of pathogenic trypanosomes infecting African cattle : T. congolense, T. brucei, T. vivax, or related species of the same groups, are found in the tolerant cattle. It appears that, in the N'Dama, the percentage infection by T. congolense is definitely higher than that of the other pathogenic species. Figures for the percentage of N'Dama animals showing detectable parasitaemia give variable results according to localities and to times of the year. This percentage, often low, reaches 11 to 15 percent in the case of average infestation. However, much higher values can be observed.
Date are more numerous for the small ruminants - sheep and goats. Allonby, in his paper for this meeting, mentions observations made in East Africa from which he shows that infection levels vary according to the season and to the density of the tsetses. The predominant species in T. congolense while T. vivax occurs only occasionally.
The methods used in epizootiological studies must be improved as soon as possible; besides making blood smears (both thin and thick film) we must resort to capillary tube centrifuging which enables us not only to make more precise observations on the parasitaemia but to measure the degree of anaemia. At the, same time we must pursue investigations by serological methods.
In addition to the studies being presently carried out in some countries there is room for beginning, or following up, investigations wherever there are trypanotolerant cattle.
Finally, trypanotolerant cattle must be studied for diseases other than trypanosomiasis, especially tick-borne diseases (particularly the rickettsioses) and the astro-intestinal parasitises.
1.5.2 Pathology
Cattle belonging to trypanotolerant breeds very often show trypanosomes in their blood without clinical manifestations of the disease.
In certain circumstances - massive challenge by Glossina or experimental infection, intercurrent diseases (parasitosis in particular), poor management, overwork - N'Dama cattle and all the other trypanotolerant breeds can show a clinical trypanosomiasis with symptoms identical with those observed in the non-tolerant breeds namely : parasitaemia with fever, anorexia, dullness and anaemia. Some animals die in the acute phase while others enter a chronic phase.
In a few cases the chronic phase is characterized by a progressive anaemia, lack of growth or weight loss leading in some animals to a very severe state of anaemia and finally resulting in cardiac failure, but in the majority of cases it is characterized, when the exceptional challenge is no longer acting, by the disappearance of clinical signs with an intermittent parasitaemia that does not have any subsequent harmful effect on the animal
2. CURRENT ACTIVITIES
2.1 Research on the mechanism of trypanotolerance and epizootiology and pathology of trypanosomiasis in trypanotolerant cattle
Research on the epizootiology and pathology of trypanosomal infections in trypanotolerant cattle is currently in progress in a number of countries. In countries with large populations of trypanotolerant cattle the prevalence of trypanosomiasis is under routine surveillance by standard diagnosis methods as, for example, in Senegal, Burkina Faso, Cote d'Ivoire, Zaire and Nigeria.
Two extensive research projects are in progress in Gambia, the first is a cooperative project involving the Government of Gambia and the University of Glassgow who are making a detailed study of the epizootiology of trypanosomiasis in N'Dama cattle exposed to natural infection by Glossina morsitans and G. palpalis. A high seasonal infection rate has been found in these animals, notably with T. congolense. Particular attention is also being given to other features of infection including clinical studies, pathogenesis and pathology.
The second project involves collaboration between the Government of Gambia and ILRAD. In this work large groups of N'Dama and zebu cattle have been infected with graded numbers of T. congolense transmitted by syringe passage to obtain data on dose response. The effects of infection are being studied in terms of parasitaemia and haematological parameters, many aspects of the immune response including antibody formation and function, cell mediated immunity, serodiagnosis, levels of complement, conglutinin and properdin. The work also includes tests for a variety of serum biochemical constituents and enzymes with possible value as factors indicating trypanotolerance. Routine pathological studies also form part of the work.
The Nigerian Institute for Trypanosomiasis Research is also currently involved in studies on the pathogenesis of trypanosomiasis in N'Dama cattle and their work has focused interest on disorders of the reproductive system in infected animals.
Sheep and goats comprise a major proportion of the livestock population in or near endemic trypanosomiasis areas and significant studies on the epizootiology of the disease and on trypanotolerance in these animals are in progress in Kenya. Indigenous breeds of both ruminant species exhibit greater tolerance towards the disease than exotic breeds. In view of the suggestion of an association between trypanotolerance and haemoglobin types, it is perhaps important to note that, no relationship between haemoglobin types and trypanotolerance has been detected either in sheep or goats.
In addition to work in Africa, several laboratories elsewhere are conducting research on immunity to trypanosomiasis which has a bearing on trypanotolerance. Studies at IEMVT in Paris are concerned notably with the haemoglobin types of many varieties of African cattle and also include the exploration of a wide range of tests for biochemical constituents which might be of value in characterizing trypanotolerance and differentiating between stock of zebu and taurine breeds. These include transferrins, albumin, IgG, IgM and various enzyme systems. At the Liverpool School of Tropical Medicine and the Centre for Tropical Veterinary Medicine in Edinburgh University, work is in progress on the production and estimation of serum immunoglobulin levels in trypanosomiasis and on serodiagnostic tests which have been applied to material from N'Dama and Muturu cattle on a limited scale. Other organizations are also contributing observations from basic research which could have a bearing on trypanotolerance.
2.2 Programme for genetic improvement of trypanotolerant breeds
2.2.1 Selection
Cote d'Ivoire. A N'Dama herd was started in 1936 at Korhogo. In 1949 it was transferred to Bouaké and it has been selected for growth rate and milk yield - the latter based on growth rate of calves from birth to 70 days. All records are available on computer. After the first 8 years progress was measured by comparing with the original unselected population. It was estimated that 25 percent of the improvement had been genetic and the rest due to improvement in feeding, management, etc. The improved animals are being multiplied on three ranches.
A multiplication ranch was established in 1961 at Abokouamékro where the performance of the animals has been studied. Considering the poor quality of the foundation parents some very fine N'Dama have been produced. More than five years ago a second ranch was opened at Sipilou, near the Guinea boarder, and a third is being set up thanks to money from FED. At the moment these three ranches comprise about 10 000 head of cattle.
These ranch animals serve several purposes: the essential justification fro this improvement programme is that it provides the farmers with parents of high quality in view of the absence of adult bulls in a great many of the herds. SODEPRA, which directs the ranches, is also responsible for all the necessary precautions and for advisory service. The ranch males are also used in feeding trials by progressive farmers who have established stands of Stylosantes. Lastly, the heifers and bulls of these ranches have served to form further breeding nuclei from which their qualities can be spread as widely as possible.
Thus genetic improvement in this country has undergone a complete development, first at centres, then on multiplication ranches and finally in practical application by the peasants.
In the northern zone a genetic improvement programme has been developed by specialists from INRA. The Cote d'Ivoire Ministry of Scientific Research has included the study of the N'Dama and Baoulé breeds and their genetic improvement in the 1976 France-Cote d'Ivoire programme. Two geneticists have been trained to carry out the programme which is due to commence at once.
In the south of Cote d'Ivoire an FAO/UNDP project is working with SODEPALM on the raising of cattle under oil palms. They have a breeding programme with Baoulé cattle which includes regular weighing and recording of mortality (which is very low). Such herds could usefully provide blood samples for typing.
Senegal. In Casamance (Kolda) in an area of G. palpalis and G. morsitans a 1 400 ha ranch was formed 18 months ago to select N'Dama cattle and dwarf sheep and goats. The present cattle population is 222 of all ages.
Guinea. An FAO consultant (Mongodin) has recently visited the country to prepare a project for the selection of N'Dama cattle. He recommended two centres for the study, selection and multiplication of this breed. The Government and UNDP have approved a project for preparatory assistance to start during 1976.
Benin. The FAO project concerned with draught animals in agriculture is now collecting information on the fattening of Lagune and Borgou cattle as well as their use for draught. It is intended also to study genetic improvement.
2.2.2 Crossbreeding
Cote d'Ivoire. At Bouaké station in Cote d'Ivoire a crossbreeding programme with the jersey breed was started in 1965. The F1 animals showed much improved milk yield and still retained some trypanotolerance. 3/8 Jersey, 5/8 N'Dama seems to be the most favourable ratio. However, it is clear that crossbreeding cannot be recommended except where improved feeding and management conditions can be supplied.
Nigeria. N'Dama bulls are distributed to traditional farmers and to farm cooperatives to upgrade the Muturu and Keteku breeds.
Sierra Leone. The Department of Agriculture has an experimental project of crossing N'Dama with Sahiwal to improve milk yield.
2.3 Development programme for rearing trypanotolerant cattle
Within the framework of the FAO campaign against animal trypanosomiasis in Africa, l'Institut d'Elevage et de Médecine Vétérinaire des Pays Tropicaux, with financial help from the French Ministry of Cooperation, is carrying out a survey on the trypanotolerant cattle breeds in West Africa and the conditions under which they are exploited in areas where trypanosomiasis is enzootic. The results of this work should be available towards the end of 1976.
2.3.1 Industrial type establishments
Congo. The Dihessé ranch in the People's Republic of the Congo has been set up in the Niari Valley, a rich area with good pasture where high yielding forage crops can be grown. The aim is to introduce 20 000 N'Dama cattle. Finance is coming from the World Bank and from France who will supply the upper level of administrative staff. So far there are 2 500 – 3 000 head on the ranch.
Nigeria. The Western Livestock Company, recently formed by cooperation between the Federal Government and the World Bank, is creating five intensive ranches in the Oyo province of Western State. Two are already started. They will produce breeding stock for sale to farmers and will fatten lean trade cattle and steers on the heavy wet-season pasture growth. Each ranch will carry 6 000 females and 350 males, mostly N'Damas, but in some ranches the females will be of the Keteku breed. When fully stocked and after about 12 years from establishment the five ranches should produce 19 000 head of cattle annually.
2.3.2 Intensive feeding
The N'Dama is an animal which reacts well to one hundred days of intensive feeding. Trials made at Bouaké in Cote d'Ivoire have resulted in weight gains of the order of 500 to 600 grams a day and conversion rates of 6 to 7 feed units per kg of live-weight gain.
Trials made at Dakar using concentrates and no natural pasture have shown that the N'Dama can put on 900 grams of live-weight per day.
N'Dama beef has a high level of palatability.
SODEPRA in its operations in the north of Cote d'Ivoire has established a system, which has given encouraging results, whereby the peasants rear animals both for work and for meat.
3. PROPOSED RESEARCH AND DEVELOPMENT PROGRAMMES
The Board of ILCA has given high priority to research on animal production in the humid tropics. This will include the formation of a network of national and international organizations to build a programme dealing with systems of animal production to be studied by multidisciplinary teams including specialists in animal science, economics, sociology, environmental and physical sciences. The programme will include many locations and a large number of animals among which will be the trypanotolerant types of cattle, sheep and goats. Several countries, representative organizations and laboratory directors present at the Consultation on the FAO Programme for the Control of African Animal Trypanosomiasis held in Accra in December 1975, have given agreement in principle to such cooperative work.
ILCA and ILRAD are among the international institutes of the CGIAR sponsored by the World Bank, UNDP and FAO. The cooperation between them will be very close as indicated in their memorandum of agreement.
3.1 Research on trypanotolerance
3.1.1 Field studies aimed at increasing the use of trypanotolerance species
1. The research in West Africa involving collaboration between the Government of Gambia, the University of Glasgow and ILRAD should be continued and similar programmes should be initiated in other countries with different ecological conditions.
2. There should be standardization of sampling method and analytical methods, as far as possible, in the research on trypanotolerant species.
3. More research is needed on the epidemiology of infection in trypanotolerant livestock including the definition and quantification of levels of trypanotolerance on an international basis.
4. The limits of trypanotolerance under different challenges need to be defined. Research should be undertaken to determine the pathogenicity of the Trypnaosoma-Glossina complex under different conditions.
5. An investigation should be made of the use of trypanocidal drugs to control clinical manifestations in trypanotolerant animals but also to facilitate the development of trypanotolerance and possibly increase its level.
6. The epizootiology of trypanosomiasis of wild animals should be studied.
3.2.1 Studies more appropriately carried out under laboratory conditions
7. Knowledge should be strengthened on biochemical aspects of trypanotolerance including serum constituents, enzymes, haemoglobins, haematological parameters, blood groups and pathology.
8. Studies on immune response should be continued, especially as related to major histocompatibility types.
9. Immunoglobulin and other macroglobulin allotypes should be investigated.
10. Attempts should be made to establish relationships between genetic markers in the blood and trypanotolerance.
11. Further work is required to evolve a sero-diagnostic test specific for different trypanosome species.
12. Basic research on aspects of trypanotolerance should also be made on wild animals.
13. There should be the closest collaboration between the proposed research in the field and the laboratory work.
3.1.3 Training
14. In order to maximize the participation of research workers and field staff in Africa, in the overall development programme on trypanosomiasis, a training programme will be necessary.
3.2 Breeding of trypanotolerant animals
3.2.1 General
Environmental influences, as well as genetic ones, influence the phenotype of an animal and this must be borne in mind when designing selection experiments. Production (in meat animals) is essentially a function of reproductive rate and growth rate.
Selection of males for traits such as growth rate and disease resistance must be very intense while for females the most important function is reproduction.
Selection for traits not associated with production should be avoided; in particular breed standards based on “fancy points” (of colour or conformation) should not be established.
A multi-disciplinary approach is necessary so that interrelationships among the various parameters can be explored. This calls for cooperation between different organizations and different countries so that available resources can be fully exploited.
3.2.2. Recommendations
1. Continuation of existing selection programmes should be encouraged but also new selection programmes to produce animals of superior genetic merit for production and disease resistance must begin as soon as possible. The objectives must be well defined and the plan simple.
2. Criteria of trypanotolerance suitable for such selection programmes need to be clearly defined and efficient. If necessary research must be directed to the definition of suitable criteria.
3. Emphasis should be on comparisons between animals in a given environment rather than measurement of absolute values. For this purpose, a reference strains could be useful; it would be represented at all research stations and measurements on other strains and crosses would be expressed as differences from the control strain.
4. Genetic gains made by selection should be measured e.g. by measuring differences from an unselected control population maintained under the same conditions.
5. Among existing and new breeding programmes, an effort should be made to coordinate objectives and methods of selections. Contacts and exchange of information between the organizations concerned can only lead to improved overall efficiency.
3.2.3 Model breeding programme for beef cattle in the tropics
This programme is expressed in general terms. It would need to be modified for specific environmental or market conditions, or to suit different breeds or populations.
1. Cull all cows which do not produce a calf each year provided that the herd size is maintained. This culling depends on the number of heifers available. Certainly old cows with a poor reproductive history should not be maintained in the herd. Cows should be culled on the weaning weight of their calves only if a very high calving rate per annum has been achieved.
If scope exists for selection among the heifers available for replacements, then they should be selected on their body weight at mating irrespective of age. In tropical environments it has been shown that the heaviest heifers have the greatest chance of calving.
2. Bulls should be selected on weight-for-age as close to the target slaughter weight as possible. Weight-for-age which includes birth weight and weaning weight, has been found to be the most efficient criterion for selection. Weight gains, either pre- or post-weaning, have in general been of low efficiency. However, in comparing breeds or crosses of very different size, the relative growth rate (rate of gain divided by mean live weight) may be a better criterion. If some selection must be made at weaning the minimum possible should be culled at that age.
3. Under research conditions the best of each new batch of bulls should be used each year. This allows a short generation interval. At each stage measurements should be made on the largest number of males that can be managed. The proportion culled at each stage depends on management.
4. Animals, especially the bulls, must be run under conditions similar to those in which their progeny are expected to produce. Criteria for trypanotolerance included in the selection programme must be applied with discretion. Selection on the primary trait, i.e. weight, in the presence of the disease may be more efficient than selection on the disease parameters.
3.3 Production economics of trypanotolerant cattle
3.3.1 General
1. FAO is conduction a study financed by UNDP on the general economics of trypanosomiasis, particularly in order to compare the cost and advantages of the different methods of combatting it with those of breeding trypanotolerant animals.
2. It is not possible in the short or medium term to envisage the total eradication of tsetse flies, especially in the forest or pre-forest zones, nor the application of radical methods for protecting the herd.
3. We know that the keeping of trypanotolerant animals in West Africa is traditional and that it is being developed by breeding and selection. In Central Africa, on the other hand, we must proceed in general by the introduction of new herds, by the creation of industrial units or by the distribution of breeding nuclei. This is why the spread of trypanotolerant cattle is the best method of stocking the regions in which the campaign against tsetse flies is not technically or economically feasible.
4. The methods outlined above, involvement of the peasants or the setting up of breeding units, are very costly. these expenses represent the infrastructure required to provide a complete service: training of the breeders and the extension agents, establishing health services, setting up systems of recording, of production and of marketing.
5. Such a service must not deal only with cattle. In order to ensure a harmonious development small units of sheep and goats must also be established.
3.3.2. Performance
1. Work. Because the farmers use cattle as working animals, trypanotolerance individuals can be introduced into the agricultural system without much risk and without straining the technical competence of the peasants.
2. Meat. The production of meat animals tends more and more to be achieved by commercial or peasant feeding methods using the by-products of agriculture and resulting in heavier carcasses. Marketing arrangements for live animals and for meat must be improved, especially by using improved means of transport and of storage wherever possible.
3. Milk. The milk production of trypanotolerant animals is poor and it supplies only the needs of the owners or of some small places in the breeding area. In order to supply the large towns of the region, commercial units must be established using stall feeding which demands the use of high yielding animals. The elaborate environment required for this type of production practically eliminates the risks of trypanosomiasis and thus makes it possible to dispense with trypanotolerant breeds.
4. All animal enterprises in the tsetse areas present, in more or less acute form, the problem of competition with agricultural development. Hopes of increasing animal production for work, milk and meat can only be realized if animal nutrition can be improved by using the by-products of agriculture and by inserting forage crops into the rotation as well as improving the fallows.
3.3.3 Health problem
The moving of animals involved in the introduction of trypanotolerant breeds is often effected without proper health inspection and so the risks of spreading contagious diseases are very great. The size of the demand can lead to animals being offered which are unfit for introduction. Great attention must be paid to inspection.
