Abstract. Title of the paper: Biotechnical control of reproduction in sows and the opportunity of a hidden change of gene frequency for estrous behaviour
Since more than three decades hormones have been used for the synchronisation of ovulation in sows often combined with timed artificial insemination. This will be done without considering the estrous behaviour. A selection with regard to symptoms of standing behaviour is not necessary. Regarding to that it is possible to breed pigs that are not suitable for that purpose.

The aim of this study was to examine the opportunity of hidden gene frequency changes in the genetics of pigs in two herds of German Landrace. This will be shown by the example of the standing behaviour and especially the time they need to come in heat after weaning of the piglets.

The basic datas was provided by two pig-breeding farms. The calculation is based only on the information to the 2nd and 3rd litter of these sows in order to reduce the influence of selection. It is assumed that the path of heredity is monofacturial. Only pigs with the genotype “aa” will be negatively affected. At the beginning the father of boars (SS) is the sole carrier of the defect gene. The gene frequency, frequency for homozygotes and the correct number of concerned pigs after 10 generations will be calculated for a more accurate description of the expansion of this gene.

The gene frequency results in the balance of 0.4 %. This figure has already been achieved after eight generations. According to this value the frequency of homozygotes is 0.0017 % on all paths of heredity. After ten generations the population will contain 0.0093 animals of the homozygot recessive genotype “aa”. There will be 0.0055 male and 0.0038 female pigs of the negative genotype.

Finally, no negative effect of the usage of hormones for the synchronisation of ovulation in pigs has been proved.