This article is published with the kind permission of the Director, Kenya Trypanosomiasis Research Institute (KETRI), PO Box 362, Kikuyu, Kenya, where the author can also be contacted.
L'Institut de recherche sur la trypanosomiase du Kenya a étudié pendant plus de 15 ans les bovins de la race Orma Boran dans la région du fleuve Tana au Kenya, infestée par la mouche tsé-tsé. Ces bovins, par rapport à d'autres races d'Afrique de l'Est, ont démontré une certaine tolérance à la trypanosomiase. Ils ont des taux de morbidité et de mortalité inférieurs et requièrent moins de traitements. Un programme de sélection a été mis en place afin d'améliorer les caractéristiques de production de viande de ces bovins tout en conservant leur trypanotolérance. Les taureaux issus de ce programme de sélection sont aujourd'hui vendus aux éleveurs dans d'autres régions du Kenya infestées par la mouche tsé-tsé.
El Instituto de Investigación sobre la Tripanosomiasis de Kenya ha estudiado durante más de 15 años los vacunos Orma Boran, de la zona infestada por la mosca tsetsé del río Tana, en Kenya. En comparación con otras razas de Africa oriental, estos vacunos han mostrado un grado considerable de resistencia a la tripanosomiasis. Tienen menor morbilidad y mortalidad y requieren menos tratamientos. Se ha organizado un programa con objeto de mejorar las características de producción de carne de este ganado, manteniendo al mismo tiempo su tripanotolerancia. Ahora se están vendiendo toros procedentes de este programa de mejoramiento a los agricultores de otras zonas de Kenya infestadas por la mosca testsé.
The indigenous cattle of Africa are the product of generations of natural selection in the face of drought and disease. Trypanosomiasis, transmitted by tsetse flies, is widespread throughout much of sub-Saharan Africa and has taken its toll on cattle in tsetse areas over the centuries. Cattle breeds with varying degrees of resistance to the disease have thus evolved, and the term trypanotolerant is used to describe livestock which exhibit some natural resistance to trypanosomiasis. The term is generally associated with Bos taurus cattle in West Africa; N'Dama cattle in particular exhibit a highly developed trypanotolerance which has been the subject of many research investigations. In contrast, trypanotolerance among East African breeds, although reported as early as 1913 (Balfour, 1913), has been largely ignored.
The tsetse distribution maps of Africa indicate a less concentrated
distribution of tsetse flies in East Africa than in West and Central Africa. There is also
evidence to support the hypothesis that Bos taurus cattle arrived in Africa many
centuries before Bos indicus cattle (Epstein and Mason, 1983). Thus the Bos
indicus cattle of East Africa have been exposed to trypanosomiasis for a shorter
period than the Bos taurus cattle of West Africa. Nonetheless, large areas of East
Africa are infested with tsetse fly and it is only in this century that drugs or tse-tse
control have afforded some protection from the disease. It is not surprising, therefore,
to find that natural selection for resistance to trypanosomiasis has also occurred
among the indigenous zebu cattle of East Africa. The Boran type cattle of the Orma people in the Tana River district of Kenya is an indigenous Bos indicus breed which has been shown to be superior to other Bos indicus cattle under tsetse challenge (Njogu et al., 1985; Dolan et al., 1994).
The Oromo people from Borana Province in Ethiopia are believed to have reached Kenya between 1400 and 1500 and their descendants now raise their Boran type cattle in the Tana River district. The southern portion of the district is heavily infested with tsetse fly while, in the northern drier areas, the fly is primarily confined to the Tana River where the Orma people water their cattle throughout most of the year. In the wet season they seek grazing away from both the river and the fly as long as supplies of standing water allow. The Orma people pride themselves on their cattle-keeping abilities and select their cattle for milk production.
These cattle have been studied by the Kenya Trypanosomiasis Research Institute (KETRI) on Galana Ranch in the Coast Province of Kenya. This 708 million ha ranch borders the grazing lands of the Orma to the east and north and Tsavo National Park to the west. The main constraints to cattle production on the ranch are predators, trypanosomiasis and lack of water. The ranch supports a large population of wild mammals and more than 30 percent of the area is heavily infested with tsetse fly. It has been the practice for many years on Galana Ranch to purchase steers for fattening from the Orma tribe. The home-bred cattle on the ranch are also Borans but these originated from the Laikipia district in the Kenyan highlands. There, in the absence of trypanosomiasis, they had undergone 70 years of selection for beef production and are known as the improved Kenya Boran.
The differences between these two types of Boran cattle under tsetse challenge were first recognized on Galana Ranch in the earlier 1980s. Studies have been conducted comparing both steers and breeding animals. In all cases it has been found that the Orma Borans do better than the improved Kenya Borans under tsetse challenge. They become infected less often, particularly with Trypanosoma vivax. Once detected as being parasitaemic, they are less likely to suffer from severe anaemia and in some cases they recover without treatment. Infection and mortality rates in the Orma are approximately half those observed in the Kenya Borans. Under both prophylactic and treatment regimes the Orma cattle require fewer drugs. However, the Kenya Borans are a better beef animal; they generally grow faster and reach a heavier mature body size than the Orma Borans. However, this trend is reversed under very high tsetse challenge.
Map of Kenya, showing Galana Ranch and tsetse-infested areas
Carte du Kenya - Situation du ranch Galana et régions où l'on rencontre la mouche tsé-tsé
Mapa de Kenya, en el que se indica la ubicación de la explotación ganadera Galana y las zonas donde está presente la mosca tsetsté
Orma Boran cattle
Bovins de race Orma Boran
Bovinos Orma Boran
Photo/Foto: D. Elsworth, ILRI
In 1983, KETRI embarked on an ambitious breeding and selection programme
aimed at improving the beef production characteristics of the Orma Boran while at the same
time maintaining their level of trypanotolerance. A breeding herd of 100 Orma cows was
established and, to date, more than 900 calves have been born. Bulls are selected for
breeding on the basis of their post-weaning growth rates. The entire herd is maintained
under constant tsetse challenge. Packed cell volume (PCV) is measured every two weeks and
blood examined for parasites. Animals infected with trypanosomes are treated when there is
a significant drop in PCV. The management regime is such that mortality due to
trypanosomiasis still occurs. This ensures that an element of natural selection for
trypanotolerance is combined with artificial selection for beef production traits.
Young Orma calves have been shown to be more resistant to trypanosomiasis than older animals. The majority of calves remain aparasitaemic between birth and weaning and mortality in calves owing to trypanosomiasis is extremely rare. Female calves are more resistant than their male counterparts. There is evidence of an ability to acquire immunity to Trypanosoma vivax infection; T. vivax incidence decreases with age while T. congolense incidence increases with age. Data have been collected to provide estimates of various genetic parameters, thereby increasing our understanding of the disease and its impact on production and also providing guidelines for improved selection programmes.
The growing human population in Kenya has given rise to an increased demand for livestock products. However, the climatic conditions and the disease constraints are such that improved exotic breeds cannot be maintained in many areas. Increasing livestock production through the use of improved indigenous breeds is an important option. The Orma breeding programme has produced calves with improved birth and weaning weights and bulls which reach 400 kg by four years of age. These bulls are now being sold to farmers in other tsetse-infested areas of Kenya, and KETRI is planning a multiplication programme to ensure the successful commercialization and utilization of Orma cattle.
Balfour, A. 1913. Animal trypanosomiasis in the Lado (Western
Mongalla) and notes on tsetse flytraps and on an alleged immune breed of cattle in
southern Kori-ofan. Ann. Trop. Med. Parasitol., 7: 113-120.
Dolan, R.B, Alushula, H., Munga, L., Mutugi, M., Mwendia, C., Okech, G., Sayer, P.D., Stevenson, P.G.W., Baker, R.L. & Magadi, M. 1994. The Orma Boran - ten years of field observations. In G.J. Rowlands & A.J.Teale, eds. Towards increased use of trypanotolerance: current research and future directions, p. 71-79. Nairobi, ILRAD/ILCA.
Epstein, H. & Mason, I.L. 1983. Cattle. In I.L. Mason, ed. Evolution of domesticated animals, p. 6-27. London and New York, Longman.
Njogu, A.R., Dolan, R.B., Wilson, A.J. & Sayer, P.D. 1985. Trypanotolerance in East African Orma Boran cattle. Vet. Rec., 117: 632-636.