The aim of the study was to evaluate the pregnancy rate after application of the OvSynch (OVS) programme depending on the reliability of the programme implementation and the number of cows treated at the same time. Taking into account the reliability of the programme, cows were divided into five groups. Females in group I were inseminated after the initial dose of GnRH, i.e. 1-6 days after the start of the programme, in group II – on days 7-9 of the OVS protocol, after administration of prostaglandin, in group III – on day 10, after completion of the full OVS protocol and timely insemination, and in group IV – on days 11-12, after completion of the full protocol and insemination according to estrous symptoms. Cows in group V were inseminated at a later period. Additionally, cows were divided into VI groups depending on the number of animals treated simultaneously during the periodic veterinary visit. Groups A, B, C, D, E and F consisted respectively of 1, 2, 3, 4, 5 and 6 cows treated on the same day. Examination for pregnancy was performed twice – on the 28th and 56th day after insemination using an iSkan ultrasound device (Draminski) equipped with a 7.5 MHz linear probe. Large differences in mating rates were shown between farms. Taking into account the timely execution of the OvSynch programme, the highest – 42.3% – mating rate was recorded in cows in which the OVS programme was executed correctly. In the other groups it was significantly (P<0.05) lower. In the case of simultaneous OvSynch in 6 cows, the percentage of correctly executed programs amounted to 83.3% and was significantly higher than in the case of treatment at smaller groups. Using the OvSynch program, the highest pregnancy rates are guaranteed by timely administration of the prescribed injections and insemination at the appointed time. Deviation from the protocol results in a worsening of the pregnancy rate. A higher number of treated cows guaranteed a higher percentage of correctly executed OvSynch programmes. Reasons for this situation were discussed.