Breeding objectives and breeding strategies for small ruminants in the tropics.

Summary

Africa is endowed with a large and diverse range of indigenous breeds of sheep and goats. In terms of their numbers and importance in Africa and other developing countries, these small ruminants contribute immensely to the subsistence, economic and social livelihood of a large human population, especially women and children, in terms of meat, milk, hides, fibre and cashflow. This is particularly so in the rural areas of sub-Saharan Africa. Despite their physiological adaptation and ability to thrive under the prevailing harsh environmental conditions in this region, diseases and parasites are a substantial constraint to the productivity of these small ruminants. Of these, GI (gastro-intestinal) helminth parasites are the most important animal health constraint. Losses occur through mortalities, reduced production and direct costs associated with preventive and curative measures. Current control strategies for helminthosis include medication with drugs (anthelminthics), isolation of animals from parasites through grazing management and improved sanitation in management systems. In Africa, many control strategies are limited by lack of funds to purchase drugs, inefficiency of veterinary services, substandard drugs and poor management. Moreover, widespread and indiscriminate use of drugs has resulted in increasing emergence of drug resistant parasites. Fortunately, some of the small ruminants in the continent appear to be genetically resistant or tolerant to GI parasites. Therefore, an attractive and sustainable control option involves the development and farming of disease resistant livestock. A problem which has received very little attention so far, is how to deliver genetic improvement under African farming circumstances.

Among the sheep breeds with superior natural helminth resistance world-wide are the Red Maasai of East Africa, Djallonke of West Africa, the Louisiana Native, Florida Native, Navajo, Barbados Blackbelly and St. Croix. However, these breeds do not always have the most desirable production traits. In selecting the most desirable breed or breed combination and selecting within a breed, one needs to start with specifying the breeding objective. The breeding objective includes all relevant characteristics of an animal (e.g. production, reproduction, fitness and health characteristics) and assigns an economic value to each trait. The economic importance of each trait depends largely on the production circumstances. For instance, in many subsistence tropical farming systems survival in the face of multiple stresses (heat, disease, poor nutrition, etc.) is one of the most important economic traits, while increasing growth rate is of less economic value. In more intense production systems, productivity may take a higher priority. However, little information is available on breeding objective for the range of production systems and agro ecological zones in Africa. Developing breeding objectives is the first objective of this study, which is expected to provide guidance for people involved in genetic improvement programs.

Genetic progress depends on selection intensity and accuracy of breeding values. Both factors are related to female reproductive capacity. Modem reproductive techniques such as MOET (multiple ovulation and embryo transfer) and other related techniques can be used to increase reproductive rates in females. This leads to higher selection intensity and accuracy of selection and subsequently increased rates of genetic gain. These techniques also increase the rate of dissemination of tested superior genotypes in commercial populations. The latter application requires a well structured breeding population and might, therefore, have only very limited application. Alternative schemes for delivery of genetically improved stock to the farmers will be described and evaluated.

Emphasis will be placed on disease resistance and its place in the breeding objective and breeding strategy. Selection for improved disease resistance is partly hindered by the lack of good indicators/measurements to identify resistant animals. Use of information from investigation on genetic resistance to GI nematodes might provide alternative ways to genetically improve disease resistant animals (particularly to Haemonchus contortus). Identification of genetic markers linked to parasite resistance genes opens the way for marker-assisted selection (MAS), and introgression (MAI) to incorporate resistance in other susceptible breeds of sheep. This study will specify breeding objectives for sheep in the tropics, look at schemes for genetic improvement including opportunity for crossbreeding and the integration of new technologies (MAS, MAI and MOET) in breeding schemes to improve disease resistance in the indigenous and other susceptible sheep. Such breeding schemes might have consequences for genetic diversity within-and between breeds. The project will therefore focus on these issues and aims at the development of guidelines to prevent loss of genetic diversity.

The aim of this project is to identify breeding objectives for tropical small ruminants and develop sheep breeding schemes with specific attention to disease resistance. Subsequently the project aims to optimise these schemes using information from investigation on genetic resistance to GI nematodes (i.e. MAS and MAI) in conjunction with current and modem reproductive techniques to improve disease resistance in indigenous sheep breeds. Ultimately, the delivery of improved germplasm from the breeding herds to the general population and economic returns from the designed breeding schemes will be evaluated.

The project has the following objectives:
1)Identify breeding objectives for tropical small ruminant livestock.
2)Examine current breeding schemes and subsequently design scheme(s) for genetic improvement, including opportunity for crossbreeding.
3)Optimize breeding scheme(s) using information on genetic markers for parasite resistance in conjunction with current and modem reproductive techniques.
4)Develop and evaluate different strategies to deliver improved genetic material to local small-holder farmers.

Output

Thesis

  • (2004): Breeding objectives and breeding strategies for small ruminants in the tropics , Wageningen  March 1, 2004

Scientific article

  • (2002): Alternative breeding schemes for meat sheep in the tropics Proceedings of the 7th World Congress on Genetics Applied to Livestock Production pp. 215 - 218
  • I.S. Kosgey, J.A.M. van Arendonk, R.L. Bakker(2003): Economic values for traits of meat sheep in medium to high production potential areas of the tropics Small Ruminant Research pp. 187 - 202 ISSN: 0921-4488.
  • I.S. Kosgey, J.A.M. van Arendonk, R.L. Baker(2004): Economic values for traits in breeding obejectives for sheep in the tropics: impact of tangible and intangible benefits Livestock Production Science pp. 143 - 160 ISSN: 0301-6226.
  • I.S. Kosgey, A.K. Kahi, J.A.M. van Arendonk(2005): Evaluation of Closed Adult Nucleus Multiple Ovulation and Embryo Transfer and Conventional Progeny Testing Breeding Schemes for Milk Production from Crossbred Cattle in the Tropics Journal of Dairy Science pp. 1582 - 1594
  • I.S. Kosgey, R.L. Baker, H.M.J. Udo, J.A.M. van Arendonk(2006): Successes and failures of small ruminant breeding programmes in the tropics: a review Small Ruminant Research pp. 13 - 28

Publications for the general public

  • I.S. Kosgey, J.A.M. van Arendonk, R.L. Bakker(2001): Breeding objectives for meat sheep in smallholder production systems in the tropics
  • I.S. Kosgey, J.A.M. van Arendonk, R.L. Bakker(2002): Importance of intangible benefits in the breeding objective of sheep in the tropics

Details

Project number

WB 82-257

Main applicant

Prof. dr. ir. J.A.M. van Arendonk

Affiliated with

Wageningen University and Research Centre, Wageningen Institute of Animal Sciences

Team members

Dr. I.S. Kosgey

Duration

01/03/2000 to 01/03/2004