Parameters of probability of gene origin of Gir herd

The objective of this study was to evaluate the genetic variability of Gir breed by the probability of gene origin parameters (PAR). The animals were belong from the beef herd of Instituto de Zootecnia localized in Sert?ozinho/SP. The herd was genetically improved using the weight after weaning as criteria for selection and the use of the breeding bulls born just within the herd. Records of 3,826 animals born between 1928 and 2012 were considered for total population (TPOP). A second population denominated recent population (RPOP) was defined with animals born between 2000 and 2012, comprising 586 animals allowed observing the last two most recent generations. The ENDOG program was used to calculate PAR: effective number of founders (f?) of ancestors (f?) and founder genomes (f_g). The f?, f? and f_g parameters refer, respectively, to the variability of the expected contributions of the founders, the bottleneck effect (fewer unrelated animals) of pedigree and the random additional loss of genes during Mendelian segregations. The bottleneck effect (BO) is calculated by the ratio between f_e and f_a (f_e/f_a) and indicates the reduction of population size and low genetic variability. The results obtained for f_e, f_a and f_g were respectively 23, 22 and 19 for the TPOP and 18, 14, 6 for the RPOP. The f_e values were low and may be attributed to the small number of founders in use in the two periods considered. The values of f_e/f_a were 1.05 for TPOP and 1.29 for RPOP. The values obtained for f_e/f_a were close to 1, considered as optimal value, but indicated that the BO is not present in general population, but starts in more recent population causing the loss of founders. Value of f_g was low for RPOP considering the number of animals presents in this population, suggesting decrease of the genetic variability. The results of PAR suggest low genetic variability in RPOP, with the possibility of loss of founder genotypes in next generations. However, it should be considered that the parameters were obtained in herd with small numbers of animals and formed by the use of sires from own herd. In the analyzed population structure it is recommended to control inbreeding and increase the number of breeding bulls in mating, for increase the genetic variability of next generations.