Gonadorelin diacetate

The objective was to determine luteinizing hormone (LH) secretion and follicular dynamics in cattle following administration of 3 gonadorelin formulations that are commercially available in Canada. In experiment 1, nonlactating Holstein cows (n = 4 per group) were randomly assigned to receive 100 micrograms gonadorelin diacetate tetrahydrate, intramuscularly (C; Cystorelin, or FE; Fertagyl). Blood samples (for LH analysis) were collected 0, 1, 2, and 4 hours after treatment. In experiment 2, nonlactating Holstein cows (n = 10 per group) were randomly allocated to receive 100 micrograms gonadorelin, intramuscularly as follows: 2 mL of C; 1 mL of FE; or 2 mL of Factrel (FA, gonadorelin hydrochloride). Gonadorelin treatment was done on days 6 or 7 after ovulation and blood samples for LH analysis were collected at 0, 1, 2, 4, and 6 hours after treatment. Ovaries were examined by ultrasonography, twice daily, to detect ovulation. A replicate was conducted using only C (n = 10) or FE (n = 10); blood samples were collected at 0, 1, 2, 3, and 4 hours. In experiment 3, beef heifers (n = 10 per group) were randomly assigned to receive 1 of 3 GnRH gonadorelin treatments (as in the first phase of experiment 2) on days 6 or 7 after ovulation and blood samples were collected at 0, 0.5, 1, 1.5, 2, and 4 hours. In experiments 2 and 3, both mean and mean peak plasma LH concentrations were higher (P < 0.05) in cattle treated with C. The proportion of dominant follicles that ovulated was higher (P < 0.02) in Holstein cows treated with C than in those treated with FE or FA (18/19, 11/19, and 4/7, respectively), but there was no significant difference among the products in beef heifers (6/10, 6/10, and 4/10, respectively). No significant differences were found in the interval from treatment to the emergence of the next follicular wave. In summary, C induced a greater LH release and this resulted in a higher ovulatory rate in Holstein cows but not in beef heifers.

Different GnRH products are used for timed artificial insemination (AI) in postpartum dairy cows. Previous studies reported greater LH release and increased ovulation percentage for gonadorelin diacetate tetrahydrate compared with gonadorelin hydrochloride but pregnancies per AI (P/AI) were not evaluated. The objective, therefore, was to compare P/AI for cows treated with either gonadorelin hydrochloride or gonadorelin diacetate tetrahydrate before the first timed AI or resynchronized timed AI. Holstein cows (n = 3938) in a confinement dairy in northeast Missouri were assigned to weekly cohorts (n = 22) on the basis of calving date. Cows were treated with "Presynch Ovsynch" (PGF2α, 14 days; PGF2α, 14 days; GnRH, 7 days; PGF2α, 56 hours; GnRH, 16 hours; timed AI) so that the first timed AI was 70 to 76 days postpartum. The PGF2α was Lutalyse (5 mL; 25 mg; Zoetis). The GnRH product was either gonadorelin hydrochloride (2 mL; 100 μg; n = 1945) or gonadorelin diacetate tetrahydrate (2 mL; 100 μg; n = 1993) and alternated weekly for cows assigned to cohorts. There were first timed AI (n = 1790) and resynchronized timed AI (n = 2148) cows within each cohort. The resynchronization began 32 days after timed AI (GnRH, 6 days; ultrasound pregnancy diagnosis, 1 day; and then for nonpregnant cows: PGF2α, 56 hours; GnRH, 16 hours; timed AI). The trial was conducted from January to February 2012 (n = 1203) and July to October 2012 (n = 2735). Cows were fed a total mixed ration, milked thrice daily, and milk tested monthly for volume, somatic cell count (SCC), fat percentage, protein percentage, and milk urea nitrogen. Data were analyzed by fitting the binary response data to a generalized linear mixed model for repeated measures. There was no effect of the GnRH product (treatment) on P/AI (38.4 ± 1.2 vs. 35.7 ± 1.3; gonadorelin diacetate tetrahydrate vs. gonadorelin hydrochloride). Treatment interactions with parity, month of breeding, or insemination number were not significant. The first-service P/AI (38.8 ± 1.4%) was greater (P < 0.05) than the resynchronized P/AI (35.3 ± 1.3%). Cows inseminated in the summer had lesser P/AI (effect of month; P < 0.001) compared with cows inseminated in the winter. There was a decrease (P < 0.002) in timed AI conception for cows with a greater milk SCC and an increase (P < 0.003) in P/AI for cows with a greater milk protein percentage. In conclusion, the GnRH product did not affect P/AI for the first or resynchronized timed AI in an Ovsynch-based program. Other factors affected P/AI including service number (lesser for the second service or greater), month (lesser in summer months), SCC (lesser for cows with greater SCC), and milk protein percentage (greater for cows with greater protein percentage).

Our aim was to assess the GnRH-induced LH surge profile in dairy cows receiving two GnRH products (gonadorelin vs buserelin) given at proestrus or diestrus phase and to investigate whether season could alter LH surge profile in dairy cows. In Experiment 1, dairy cows at 108.2 ± 2.3 DIM, producing 41.5 ± 0.3 kg/day were randomized to receive, during proestrus and diestrus: Ovarelin® i.m. (OVA; n = 56; 100 mg of gonadorelin diacetate tetrahydrate; Ceva Animal Health, France) or Receptal® i.m. (REC; n = 52; 10 mcg of buserelin diacetate; MSD, Germany). In Experiment 1, blood samples were collected at hour 0 (just before GnRH treatment) at 30min, 1 h and then hourly until 5 h post-GnRH. In Experiment 2, cows were synchronized with a modified G-6-G protocol and randomized to receive either OVA or REC throughout the synchronization program. In Experiment 1, peak LH concentrations (ng/mL) were not affected by type of GnRH (OVA = 6.2 ± 0.4 vs REC = 6.7 ± 0.4; P = 0.37) or season (Cool = 6.8 ± 0.4 vs Warm = 6.1 ± 0.4; P = 0.22), and there were no interactions between GnRH type and phase of the estrous cycle or season. Interestingly, the area under the curve (AUC) of LH release (ng/ml*time) was significantly lower during warmer months (Cool = 20.3 ± 1.2 vs Warm = 16.9 ± 1.1; P = 0.04). As expected, LH peak was affected by phase of the cycle (proestrus = 8.2 ± 0.4 vs diestrus = 4.7 ± 0.4; P < 0.01). Ovarelin caused LH concentrations to increase faster, reaching highest concentration sooner (h) than REC (1.5 ± 0.1 vs 2.3 ± 0.1; P < 0.01). As a result, cows receiving OVA had greater circulating LH concentrations (ng/mL) at 1 h after GnRH treatment than cows receiving REC (P < 0.01). In contrast, cows treated with REC had longer (P = 0.01) intervals from peak until return to nadir. In Experiment 2, pregnancy per AI (P/AI) was similar for cows receiving either GnRH product during the synchronization protocol, with no detectable interactions between GnRH type and season. In conclusion, phase of the estrous cycle had a great impact on the GnRH-induced LH surge profile and cows during warm season had reduced AUC. Additionally, type of GnRH did not influence LH surge profile and P/AI in synchronized cows. Regardless of GnRH type, strategies to avoid heat stress and excessively high levels of circulating P4 near the time of GnRH treatment might help improve LH release profile in dairy cows, and ultimately increase P/AI.