The objective of this study was to examine the population genetic structure of the Brazilian Gir dairy cattle in order to assist technicians and breeders to set up mating schemes for the animals in the Gir herds and to preserve genetic diversity. Pedigree data were obtained from the herds. The sample was subdivided in genetic groups or subpopulations based on the birth date of animals to study the genetic variability among them: I - unknown birth date or born before 1965; II - born from 1966-84; III - born from 1985-92; and IV - born from 1993-2005. A complete relationship matrix included 27 610 animals with 2.82% of average inbreeding coefficient and 2.10% of average relatedness coefficient. Inbreeding coefficients ranging from 1 to 41% with an average of 4.66% was found for 16 687 animals. The average inbreeding coefficient, relatedness coefficient and percentage of inbred individuals increased steadily as the generations elapsed. The effective population size (Ne) ranged from 16.1 to 125.3. The maximum number of generations between an individual and its more distant ancestor was 22. The effective number of founders was 146, and the expected increase of inbreeding was 0.34% due to unbalanced contribution of founders. The number of ancestors contributing to the reference population was 2872. From these, only 28 were responsible by 50% of the population genetic diversity or only one percent of the animals transmitted the half of the genes of the whole reference population. A small number of ancestors contributed to Gir dairy cattle foundation, originating a homogeneous population, as gene flow was regarded, with high percentage of inbred animals. Careful mating scheme must be set up within herds, avoiding the undesirable effects of inbreeding on production and reproductive traits.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 01.91, 2006
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