Object of work. 1. Investigation of prolactin gene polymorphism and distribution of different alleles at Lithuanian cattle breeds (Lithuanian Red, Lithuanian Light Grey, Lithuanian White Backed, Lithuanian Black and White). 2 Investigation of prolactin (PRL) gene influence to milk production. Tasks of work. 1. Introduce cattle prolactin gene research methodology at K. Janušauskas Laboratory of Animal Genetics, LVA. 2. Investigate prolactin gene polymorphism at LR, LBW, LWB, LLG cattle breeds by molecular PCR-RFLP method. 3. Determine frequency of prolactin gene alleles and genotypes at LR, LBW, LWB, LLG cattle breeds. 4. Compose data base for dairy production of investigative cattle population. 5. Investigate influence of prolactin gene to milk yield, fat and proteins. Research methodology. 1. DNA extraction from: blood and hair roots. 2. PCR to amplify PRL gene. 3. RFLP method-PRL – enzyme RsaI. 3. Electrophoresis in agarose gel. 4. Staining with Etidium bromide. 5. Genotyping. Results. The following DNA restriction fragments were obtained for the PRL-RsaI polymorphism: 82 and 74 bp for the BB genotype, 156, 82 and 74 bp for the AB and 156 bp for the AA genotype. The AA genotype was found most frequent in all breeds (0.06 – 0.94), followed by the AB (0.06 – 0.37). The least frequent was the BB genotype (0.00 – 0.08). Prolactin gene A allele was found most frequent (0.97) at Lithuanian Light Grey, the least frequent (0.77) - at Lithuanian red cattle breed. Conclusions... [to full text]