Influence of deslorelin (GnRH-agonist) implant on plasma progesterone, first wave dominant follicle and pregnancy in dairy cattle

摘要

In the first of 2 experiments, 15 non-lactating cyclic Holstein cows received buserelin (8μg intramuscularly) on day -9 (day 0 = day of treatment) and Lutalyse (25 mg intramuscularly) on day -2. The animals were then divided into 3 equal groups andreceived (on day 0) a deslorelin (a GnRH agonist) implant (700μg) or buserelin (8μg) intramuscularly; untreated animals served as controls. Blood samples were collected on days minus9, minus2, 0 and thereafter daily until the next ovulation. Ovaries were scanned by ultrasound on days minus9, minus2, 0 and 1 (day of ovulation) and 3 times a week thereafter until a subsequent ovulation. From day 0 to day 15, the rate of increase of plasma progesterone was greater (P<0.01) for the deslorelin than for the control and buserelin groups. Establishment of the first-wave dominant follicle (FWDF) as a class-3 (>9 mm) follicle occurred later (P <0.01) in the deslorelin (14.2±1.3 days) than in the control (4.6±1.3) and buserelin (5.0±1.5) groups. The FWDF resumed growth after day 13 in all deslorelin-treated cows, and 2 cows ovulated spontaneously. In 1 deslorelin-treated cow, the FWDF regressed and a second-wave dominant follicle ovulated, while 2 other deslorelin-treated cows failed to ovulate until after day 36. The deslorelin group had the highest number of class-I follicles (P<0.01) and the lowest number of class 2 + class-3 follicles (P<0.01). There was no difference between treatments in the duration to corpus luteum regression or days to subsequent oestrus. In the second experiment, 16 lactating, potentially subfertile (body condition score 2.25) cows received Cystorelin (100μg intramuscularly) on day minus9, Lutalyse (25 mg intramuscularly) on day minus2 and a Cystorelin injection (100μg) or deslorelin implant (700μg) on day 0. The animals were inseminated 16 h later. Deslorelin-treated cows had a higher plasma progesterone concentration between days 0 and 16 (P<0.05) than the other group, and 5 of the 8 cows in this group were pregnant on day 45 compared with 1 of 8 cows in the Cystorelin group (P<0.05). The results show that the pregnancy rate of cows in poor body condition can be increased by deslorelin implant treatment combined with a timed insemination protocol. The results also support the hypothesis that increased corpus luteum function and delayed establishment of the FWDF increases embryo survival.