O.B. Kasali, E. Mukasa-Mugerwa, Tekelye Bekeleand
B.C. Njau
Animal Reproduction and Health Section
International Livestock Centre for Africa
P.O. Box 5689
Addis Ababa
Ethiopia
Summary
Resume
Introduction
Reproductive wastage
ILCA's proposed programme
References
Causes of reproductive wastage in small ruminants in tropical Africa are highlighted. Pre- and postnatal deaths account for most of the loss. The role of the International Livestock Centre for Africa in collaboration with the National Agricultural Research Systems in overcoming the multiple factors involved in reproductive wastage in small ruminants is outlined.
Les causes des pertes de la capacité reproductrice des petite ruminants en Afrique tropicale vent passées en revue. Les mortalités avant et après la naissance vent responsables pour la plupart des pertes. Le rôle du Centre International pour l'Elevage en Afrique en collaboration avec les Institutions nationales des recherches vétérinaires et de l'élevage pour surmonter le problème est esquissé.
About 25% of the world's 1.14 billion sheep reside between 15°N and 30°N, covering the northern half of Africa and southern Asia (FAO, 1986). Present sheep and goat production levels in this region are considered to be low. This is partly because of the harsh regional climate that forces animals to thrive at subsistence level.
The reproductive performance of sheep and goats in Africa has been reported in terms of fertility, prolificacy (litter size), fecundity (fertility x prolificacy), lambing and weaning rates (Wilson, 1982; Mukasa-Mugerwa and Tekelye, 1988). Post-natal lamb losses ranging from 12% to 68% have also been observed (Wilson, 1976; Otesile et al, 1982; Ndamukong, 1985; Wilson et al, 1985; Kasowanjete et al, 1987; Sow et al, 1987; Carles et al, 1988; Njau et al, 1988; Gautsch, 1988; Traore and Wilson, 1988). Since the biological and economic efficiency of sheep production is influenced by the number of lambs reared per ewe (Haresign, 1985), mortality-related production losses are very significant, particularly in view of the contribution of sheep and goats to the household economies of the agricultural populations of the tropics (Jones, 1972).
Reproductive wastage is normally considered to cover all losses from mating to the first breeding of the offspring. Reproductive wastage is caused by environmental, genetic, disease and management factors which operate with different severities and in different combinations. These factors interfere with ovulation, fertilization or implantation and during gestation and parturition.
Pre-natal losses
Pre-natal losses are more difficult to quantify and interpret than post-natal deaths. Losses due to fertilization failure and early embryonic mortality are costly and time-consuming to measure and, with few exceptions, have not been widely assessed under field conditions (Restall et al, 1978). The level of early embryonic death is estimated at 6% to 48% of all zygotes among temperate breeds (Edey, 1969). Many estimates, however, fail to distinguish between fertilization failure and actual embryonic death. It is important to separate the two, especially in twin ovulations, where only one zygote finally develops.
The extent of pre-natal wastage in African sheep is not extensively reported. In an abattoir study of 608 Ethiopian highland ewes, 71% were found to be pregnant, 24% of these with twins: this is in contrast to twinning rates of less than 10% under field conditions (Mukasa-Mugerwa and Tekelye, 1988). Such disparities could be partly attributed to pre-natal losses. Reducing prenatal losses could significantly increase current sheep and goat production levels.
Post-natal losses
Lamb mortality accounts for serious losses in sheep production and is thus a major factor reducing profitability of sheep farming. In the United Kingdom, neonatal mortality is responsible for approximately 35% of all sheep losses (Howe, 1976) equivalent to a loss before weaning of £26 million. Since deaths in the first week of life cause 75% of this loss (Whitelaw, 1976), the cost of neonatal mortality was approximately £20 million per year in the UK in the 1970s.
In tropical Africa, there are now some data on lamb mortality (Otesile et al, 1982; McKinnon and Rocha, 1985; Murayi et al, 1987; Njau et al, 1988; Traoré and Wilson, 1988; Wilson and Traoré, 1988). Neonatal mortality of lambs under traditional management has been estimated to range from 2% to 20% depending on nutritional status of the ewes and the time of lambing (Jones, 1972). In Cameroon, lamb mortality rates of 68.4% and 37.5% had been reported in local and exotic breeds of sheep (Ndamukong, 1985), with the majority of these deaths occurring on the first day of life. Studies in Ethiopia indicate perinatal lamb mortality of 18% (Njau et al, 1988).
Early sheep losses have been attributed to infertility and embryonic mortality (Mishap et al, 1986) and to neonatal mortality including starvation/exposure, abortion/stillbirth, infectious diseases, accidental death or loss, predators and congenital defects (Eales et al, 1983). Among the infectious causes of abortion Chlamydia psittaci (enzootic abortion of ewes) and Toxoplasma gondii are of major importance in Britain and in Africa (Linklater, 1979; Okoh et al, 1981; Zain Eldin et al, 1985). Leptospiral organisms also cause abortions, stillbirths and death of weak newborn lambs (Ellis, 1983) but the main serotypes have not been identified.
Inadequate nutrition has been shown to exert adverse effects on both ewes and lambs (Edey, 1975; Meaker and Niekerk, 1977). These effects are particularly marked in ewes bearing twins (Alexander, 1968). Mismothering as a sequel to poor prenatal nutrition of the dam may be the main cause of many early lamb losses (Wilson, 1976; Otesile et al, 1982; Njau et al, 1988).
Brucella species have been cited as one of the principal causes of abortion in sheep and goats in Africa (Chukwu, 1985; 1987). Studies on Angora goats, however, eliminated infectious diseases and mineral and vitamin deficiencies as causes of abortion (van Heerden, 1963) but incriminated nutritional stress and endocrine failure (Wentzel and Botha, 1976). Despite frequent abortions and related causes of infertility, including stillbirths and early embryonic mortalities, exhaustive investigations of the causative agents have not been undertaken (Okoh, 1980).
The strategy of ILCA in identifying, and then reducing, causes of mortality and morbidity over the next 5 yr would be an interdisciplinary approach, focusing on the interactions of the multiple factors responsible for lamb mortalities, both on-farm and on-station. The Animal Reproduction and Health Section intends to:
identify and study the epidemiology of potential causes of mortality from conception to weaning;determine the temporal and spatial clustering of these mortalities;
use the data obtained to develop health, nutritional and management packages to reduce wastage; and
test the socio-economic acceptability of the packages.
Alexander G. 1968. The environment and neonatal survival of sheep in Australia. Proceedings of the Ecological Society of Australia 3: 125-128.
Carles A B. Gachiuri C K and Schwartz H J. 1988. A comparison of goat mortality in two pastoral herds in Kenya. Proceedings of the Third International Rangelands Congress 2: 440-442.
Chukwu C C. 1985. Brucellosis in Africa. 1. The prevalence. Bulletin of Animal Health and Production in Africa 33: 193-198.
Chukwu C C. 1987. Brucellosis in Africa. 2. The importance. Bulletin of Animal Health and Production in Africa 35: 92-98.
Earles F A, Small J and Gilmour J J. 1983. Neonatal mortality of lambs and its causes. In: W Haresign (ed.), Sheep production. Butterworths, London, UK.
Edey T N. 1975. Pre-natal mortality in sheep: A review. Animal Breeding Abstracts 37: 173-176.
Ellis W A. 1983. Possible involvement of leptospires in abortion, stillbirths and neonatal deaths in sheep. Veterinary Record 112: 291-293.
FAO 1986. Production year book (Volume 40). Food and Agriculture Organization, Rome, Italy.
Gautseh K D. 1988. Comparative productivity of indigenous sheep in the highland areas of Ethiopia and Rwanda. Group Document No. SRC 14. International Livestock Centre for Africa, Addis Ababa, Ethiopia.
Haresign W. 1985. The physiological basis for variation in ovulation rate and litter size in sheep. A review. Livestock Production Science 13: 3-20.
Howe K S. 1976. The cost of mortality in sheep production in the UK, 1971-1974. Report No. 198. Agricultural Economics Unit, University of Exeter, Exeter, UK.
Jones R G. 1972. Sheep production in the semiarid areas of Africa and South Asia. In: R E McDowell (ed.), Improvement of livestock production in warm countries. W H Freeman and Co, San Francisco, USA.
Kasowanjete M, Stotz D and Zerfas H P. 1987. Goat development programme in Malawi. Small Ruminant and Camel Group Newsletter 8: 15-21.
Linklater K A. 1979. Abortion in sheep. In Practice 1: 30-33.
McKinnon D and Rocha A. 1985. Reproduction, mortality and growth of indigenous sheep and goats in Mozambique. In: R T Wilson and D Bourzat (eds.), Small ruminants in African agriculture. International Livestock Centre for Africa, Addis Ababa, Ethiopia.
Meaker H J and Niekerk C H. 1977. Birth mass and neonatal mortality of lambs as affected by level of nutrition of the ewe. South African Journal of Animal Science 7: 25-26.
Mishan M, Ulagnathan V, Rodricks I M, Bhutanakumar C K and Iyne M. 1986. Reproduction rate and viability of Merino, Nilgiri and half-bred Merino. 1. Fertility, prolificacy and viability. Tropical Animal Health and Production 18: 171-176.
Mukasa-Mugerwa E and Tekelye Bekele. 1988. The reproductive performance of Ethiopian highland sheep. Animal Reproduction Science 17: 95-102.
Murayi T. Sayers A R and Wilson R T. 1987. La productivité des petite ruminants dans les stations de recherche de l'Institut des Sciences Agronomiques du Rwanda. Rapport de recherche No. 15. Centre International pour l'Elevage en Afrique, Addis Abéba, Ethiopie.
Ndamukong K J N. 1985. Effects of management system on mortality of small ruminants in Bamenda, Cameroon. In: R T Wilson and D Bourzat (eds.), Small ruminants in African agriculture. International Livestock Centre for Africa, Addis Ababa, Ethiopia.
Njau B C, Kasali O B. Scholtens R G and Mesfin Degefa. 1988. Review of sheep mortality in the Ethiopian highlands, 1982-86. ILCA Bulletin 31: 19-22.
Okoh A E J. 1980. Abortion in sheep near Kano, Nigeria. Tropical Animal Health and Production 12: 11-14.
Okoh A E J. Agbonlahor D E and Momoh M. 1981. Toxoplasmosis in Nigeria: A serological survey. Tropical Animal Health and Production 132: 137-143.
Otesile E B. Kasali O B and Babalola M L. 1982. Mortality in sheep on the University of Ibadan teaching and research farm, Ibadan, Nigeria. Bulletin of Animal Health and Production in Africa 30: 235-239.
Restall B J. Brown G H. Blockey M B. Kahill L and Kearns R. 1978. Fertilization failure and early embryonic survival. Australian Journal of Experimental Agriculture and Animal Husbandry 16: 329-335.
Sow R. Thiongane P I and Tchamitchian L. 1987. Results of five years of research on Peul and Touabire sheep at Dakar (Senegal). Small Ruminant and Camel Group Newsletter 9: 11-17.
Traoré A and Wilson R T. 1988. Livestock production in central Mali: Environmental and pathological factors affecting morbidity and mortality of ruminants in the agropastoral system. Preventive Veterinary Medicine 6: 63-75.
van Heerden K N. 1963. Investigation into the causes of abortions in Angora goats in South Africa. Onderstepoort Journal of Veterinary Research 30: 23-25.
Wentzel D and Botha L J J. 1976. Steroid function in nutritionally stressed pregnant Angora goat does. Agroanimalia 8: 163-165.
Whitelaw A. 1976. Survey of perinatal losses associated with intensive hill sheep farming. Veterinary Annual 16: 60-65.
Wilson R T. 1976. Studies on the livestock of Southern Darfur, Sudan. III. Production traits in sheep. Tropical Animal Health and Production 8: 103-114.
Wilson R T. 1982. Husbandry, nutrition and productivity of goats and sheep in tropical Africa. In: R M Gatenby and J C M Trail (eds.), Small ruminant breed productivity in Africa. International Livestock Centre for Africa, Addis Ababa, Ethiopia.
Wilson R T and Traoré A. 1988. Livestock production in central Mali: Reproductive wastage in ruminants in the agropastoral system. Theriogenology 29: 931-944.
Wilson R T. Peacock C P and Sayers A R. 1985. Pre-weaning mortality and productivity indices for goats and sheep on a Masai group ranch in south-central Kenya. Animal Production 41: 201-206.
Zain Eldin E A, Elkhawea S E and Kheir H S M. 1985. A serological survey for Toxoplasma antibodies in cattle, sheep, goats and camels (Camelus dromedarius) in the Sudan. Revue d'Elevage et de Médicine Vétérinaire des Pays Tropicaux 38: 247-249.
