The effects of 3 gonadorelin products on luteinizing hormone release, ovulation, and follicular wave emergence in cattle.
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.
Martínez
Marcelo
M
Department of Large Animal Clinical Sciences, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B4.
Mapletoft
Reuben J
RJ
Kastelic
John P
JP
Carruthers
Terry
T
D000818:Animals; D002417:Cattle / Q000502:physiology*; D005260:Female; D005300:Fertility Agents, Female / Q000494:pharmacology*; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives / Q000494:pharmacology*; D007273:Injections, Intramuscular / Q000662:veterinary; D007986:Luteinizing Hormone / Q000378:metabolism*; D006080:Ovarian Follicle / Q000187:drug effects* / Q000502:physiology; D010053:Ovary / Q000000981:diagnostic imaging; D010060:Ovulation / Q000187:drug effects* / Q000502:physiology; D010062:Ovulation Induction / Q000379:methods / Q000662:veterinary; D011897:Random Allocation; D014463:Ultrasonography
D005300:Fertility Agents, Female; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone