The aim of the present study was to evaluate the stimulating effect of synthetic GnRH analogues without the use of prostaglandins on ovarian follicular growth dynamic and oestrus. The study was made on 30, 3 to 9-year-old Lithuanian Black and White (LBW) and German Black and White (GBW) breed cows. The study was conducted in the Lithuanian Veterinary Academy practical training and research farm. Oestrus in 23 cows was stimulated using synthetic GnRH analogues Dalmarelin (Lecirelin) (Fatro S. p. A., Italy) and in 14 cows with the use of Depherelin® (Gonavet® 50, Veyx-Pharma GmbH, Germany). Dalmarelin (Lecirelin) induced oestrus in 100% of the stimulated cows, and Depherelin® (Gonavet® 50) induced oestrus in 92.9 % of stimulated cows. Following an injection of synthetic GnRH analogues, preparations Depherelin® and Dalmarelin, plasma progesterone concentration decreased, due to the ovulation of dominant follicle or onset of the new follicular wave. Cows stimulated with Dalmarelin had a faster follicular growth rate and bigger size of follicles at ovulation compared to Depherelin® and control group cows (p = 0.05). In the pregnancy trial that followed 45 days after artificial insemination, the highest percentage (43.5 %) of pregnant cows was determined in the group of cows stimulated with Dalmarelin.
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