Use of Lecirelin to improve insemination efficiency of dairy cattle

The GnRH-analogue Lecirelin is a nonapeptide whose molecular structure differs from the natural decapeptide GnRH by replacement of glycine in position 10 with an ethylamide-group and in position 6 with D-tert.-leucine. These structural changes result in a longer binding-time at the specific hypophyseal receptors and thereby a prolonged duration of action. In a field trial, the effects of administration of 50 mu g Lecirelin at time of insemination on the first service conception rate (FSCR) considering parity prior hormonal induction of estrus (EI) and calving to first service interval (CSI) were studied on 203 cows (101 animals in experimental group [EG] and 102 in control group [CG] resp.) in 18 dairy herds. Animals of the CG received no injection and the allocation was done alternately. No difference between groups was noticed inheifers. Incows, FSCR of the EG was 50% (n = 69) in comparison to 44% (n = 65) in the CG. Animals that came into estrus spontaneously showed a tendency to higher FSCR in the EG (EG 67 % [n = 63], CG 55 % [n = 73]). This was most obvious in cows that came into estrus spontaneously (EG 67% [n = 36], CG 49 % [n = 41]). Subject to days to first service, cows that were inseminated before day 60 postpartum (p.p.) as well as those inseminated after day 80 p.p. had a higher FSCR (CSI < 60: EG 67 % [n = 18], CG 56 % [n = 27]; CSI 80: EG 39 % [n = 31], CG 26 % [n = 23]). Cows that were inseminated between day 60 and day 80 p.p. had a FSCR of 52% (EG) and 50% (CG) resp..