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Assessment of the genetic variability using pedigree analysis of the Sahiwal breed in Kenya

Published online by Cambridge University Press:  03 January 2017

S. Mwangi ,
T.K. Muasya ,
E.D. Ilatsia  and
A.K. Kahi
S. Mwangi
Affiliation:
Animal Breeding and Genomics Group, Department of Animal Sciences, Egerton University, P.O. Box 536, 20115 Egerton, Kenya
T.K. Muasya*
Affiliation:
Animal Breeding and Genomics Group, Department of Animal Sciences, Egerton University, P.O. Box 536, 20115 Egerton, Kenya
E.D. Ilatsia
Affiliation:
Kenya Agricultural and Livestock Research Organisation, Dairy Research Institute P.O. Box 25, 20117 Naivasha, Kenya
A.K. Kahi
Affiliation:
Animal Breeding and Genomics Group, Department of Animal Sciences, Egerton University, P.O. Box 536, 20115 Egerton, Kenya
*
Correspondence to: T.K. Muasya, Animal Breeding and Genomics Group, Department of Animal Sciences, Egerton University, P.O. Box 536, 20115 Egerton, Kenya. email: [email protected]
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Summary

Pedigree analysis using genealogical information of 18 315 animals born between 1949 and 2008 was done to quantify genetic variability of the Sahiwal population in Kenya. Generation intervals for sire pathways were longer than dam pathways and increased over year periods, from about 4–16 years. The later was due to use of old bulls for breeding in the last 2 year groups and cessation of progeny testing in the year 2000. Average inbreeding level in last year period studied was 1.2 percent. Genetic variability of the population as assessed based on gene origin statistics decreased over the years. The ratio of effective number of founders to founders of 0.06 showed unequal contribution of founders to the reference population. However, since the founding population, ancestors contributed equally as shown by the ratio of f e/f a of 0.94, which could also be due to lack of effective selection in this population. The ratio of f g/f a of 0.63 indicated genetic loss of genetic variability occurred through genetic drift in the Kenyan Sahiwal population. The small number of ancestors (16) that accounted for 50 percent of the total variation in the reference population suggested overuse of a small number of some animals as parents over generations. The smaller ratio of f g/f e compared with f a/f e also confirms loss of genetic variability in the population by genetic drift than bottlenecks. Therefore the breeding strategy for the Sahiwal population in Kenya should incorporate tools that balance rate of genetic gain and the future rate of inbreeding.

Résumé

Une analyse généalogique a été réalisée avec les données de 18 315 animaux nés entre 1949 et 2008 dans le but de quantifier la variabilité génétique de la population Sahiwal au Kenya. Les intervalles générationnels ont été plus longs sur la voie paternelle que sur la voie maternelle et se sont allongés au cours des années, d'environ 4 ans à 16 ans. Ceci a été dû à l'utilisation de vieux mâles pour la reproduction dans les deux dernières périodes d'années et à l'arrêt du contrôle de la descendance en l'an 2000. Le niveau moyen de consanguinité dans la dernière période étudiée a été de 1.2 pour cent. La variabilité génétique de la population, évaluée au moyen de statistiques sur l'origine des gènes, a diminué au fil des années. Le rapport entre le nombre effectif de fondateurs et les fondateurs a été de 0.06, ce qui met en évidence une contribution inégale des fondateurs à la population de référence. Cependant, depuis la population fondatrice, les ancêtres ont contribué équitablement, comme reflété par le rapport f e/f a de 0.94, qui pourrait aussi être dû à un manque de sélection efficace dans cette population. Le rapport f g/f a de 0.63 indique une perte de variabilité génétique causée par dérive génétique dans la population Sahiwal du Kenya. Le faible nombre d'ancêtres (16) expliquant 50 pour cent de la variation totale dans la population de référence suggère l'utilisation excessive en tant que parents d'un petit nombre d'animaux au cours de plusieurs générations. De même, le fait que le rapport f g/f e soit inférieur au rapport f a/f e confirme la perte de variabilité génétique dans la population par dérive génétique plutôt que par goulots d'étranglement génétique. Par conséquent, la stratégie de sélection pour la population Sahiwal au Kenya devrait intégrer des outils permettant d'équilibrer le taux de gain génétique et le taux futur de consanguinité.

Resumen

Se llevó a cabo un análisis genealógico con datos de 18 315 animales nacidos entre 1949 y 2008 con el fin de cuantificar la variabilidad genética de la población Sahiwal en Kenya. Los intervalos generacionales por la vía paterna fueron mayores que por la vía materna y aumentaron con el paso del tiempo, desde aproximadamente 4 a 16 años. Esto último se debió al uso de machos viejos para la cría en las dos últimas franjas de años y al cese del testaje de la progenie en el año 2000. El nivel medio de endogamia en el último periodo de tiempo estudiado fue del 1.2 por ciento. La variabilidad genética de la población, determinada en base a estadísticas del origen de los genes, disminuyó a lo largo de los años. El ratio entre el número efectivo de fundadores y los fundadores fue de 0.06, lo cual muestra una contribución desigual de los fundadores a la población de referencia. Sin embargo, desde la población fundadora, los ancestros contribuyeron equitativamente, tal como refleja el ratio f e/f a de 0.94, que también podría deberse a una falta de selección eficaz en esta población. El ratio f g/f a de 0.63 indicó una pérdida de variabilidad genética ocurrida por deriva genética en la población Sahiwal keniana. El pequeño número de ancestros (16) responsable del 50 por ciento de la variación total en la población de referencia hace pensar en un uso excesivo de un reducido número de animales como progenitores a lo largo de varias generaciones. También el hecho de que el ratio f g/f e sea menor que el ratio f a/f e confirma la pérdida de variabilidad genética en la población por deriva genética más que por cuellos de botella. En consecuencia, la estrategia reproductiva para la población Sahiwal en Kenya debería incorporar herramientas que equilibren la tasa de ganancia genética y la tasa futura de endogamia.

Keywords

effective population sizegenealogygenetic diversityinbreedingoptimum contributiontaille effective de la populationgénéalogiediversité génétiqueconsanguinitécontribution optimaletamaño efectivo de poblacióngenealogíadiversidad genéticaendogamiacontribución óptima
Type
Research Article
Information
Animal Genetic Resources/Resources génétiques animales/Recursos genéticos animales , Volume 59 , December 2016 , pp. 7 - 14
Copyright
Copyright © Food and Agriculture Organization of the United Nations 2016 

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