Description: The aim of the study was to analyze the overall genetic variance and effects for the prolificacy trait in North-East Bulgarian Merino sheep breed, with distinct participation of the Australian Merino and Booroola breeds in its genotype. The study included 584 pedigrees and 1123 prolificacy records. An animal model was used and the following factors were included in the statistical analysis: year of each lambing, consecutive lambing, year of birth of the animal, regression effect of age in days to the date of lambing. The average value for the prolificacy trait was 1.114 lambs per ewe with typical for the phenotypic variation trait ( 29.0 percent ). The genetic tendency for prolificacy was negative, depending on the year of birth, and positive on subsequent rearing. Analysis of the variance indicated that the major part of the genetic variance have been described, by the individual characteristics of the animals ( 0.034 at 0.001 caused by heterosis ). The proportion of genetic variance resulting from different breed combination in the genotype was extremely low relative to the individual genetic varians ( 0.257 ), which reflected the overall genetic variation. Estimates of additive and non-additive effects by genetic groups did not establish clear distinguishable differences