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The aim of this study was to stimulate the oestrus cycle and shorten the time between calving and recurring pregnancy by using GnRH and PGF2α in cows which do not show oestrus cycle until the 55th day of the postpartum. The materials of the study were 2-10 years old. 40 Holstein breed cows. These cows did not have oestrus cycle until the 55th day of the postpartum period. These animals were divided into four groups. At day 0, the 250 mcq GnRH was injected into first group. 2 PGF2α (250 mcq) injections (apart 11 days) second group. 250 mcq GnRH and on the 10th day 250 mcq PGF2α to the third group, and fourth group was kept as control. Blood samples were taken from cattle in all groups. 12 hours before injections and 12 hours intervals for 5 days. Blood collection was continued once a day on the 6th and 8th days and on the 10th – 11th days and 12 hours intervals consecutive 5 days after the second enjektion. The progesteron and oestradiol levels were measured. The animals were artificially inseminated in their first detected oestrus cycle. In the first group animals (40%). In the second group I animal became pregnant (%10) after first PGF2α enjektion and 2 animals (%28.5) became pregnant after second PGF2, injection.
In the third group 7 animals (70%) became pregnant. Signs of oestrus were observed in the 4 cows (40%) on 97.5 days after birth and 3 of them became pregnant after artificial insemination (%30). As a result; GnRH+PGF2α (on I0th day) administration, after 55th day of postpartum to stimulate oestrus cycle and ovarian activity of the high quality dairy cows which show anoestrus until 55 days after postpartum period, was supposed to give better results.