The diploma paper was focused on evaluation of chosen factors that influences loss of piglets since birth to weaning. Experiment was run in pre-chosen breeding herd on 80 sows of two genotypes A and B. The influence of genotype was evaluated for loss of piglet, then it´s influence on birth weight and sex, and for genotype A lose based on order of litter. There was statistically proven difference between genotypes in loss of piglets for litter. For genotype A the loss for litters was 1, 49 piglets and for genotype B it was 0,84 piglets for litter. There was also valid statistics prove of positive correlation between number of piglets that were born alive and number of reared piglets, however highly provable positive correlation between number of piglets born in litter and lose of piglets before weaning was established only for genotype A. When gender taken into account higher mortality of female piglet for genotype A 9,22 % than for genotype B 3,76 %. In case of male piglet the difference was not so striking 10,92 % for genotype A and 7,37 % for genotype B. The overall loss of male piglets was 5,31 % higher than for females piglets. Average postnatal weight of dead piglets did not differ for both genotypes too much (1,06 kg A, 1,02 kg B). Statistically unprovable difference was established for evaluation of postnatal weigh of dead piglets with opposite sex. During evaluation of number of piglets born alive in litter based on order of litter was established statistically provable difference between the first and the third litter and highly statistically provable difference between the second litter and the third litter. There was highly provable statistic difference in number of reared piglets between the third and the fourth litter. Highly provable statistic difference in number of dead piglets on litter between the first and the fourth litter and also between the second and the fourth litter was established. In a lose percentage was established statistically provable difference only between the second and the fourth litter.