Study summary · research use only
The effects of 3 gonadorelin products on luteinizing hormone release, ovulation, and follicular wave emergence in cattle
Plain-language summary
Paraphrased from the published abstract below — not a verdict on whether anything works.
This study in nonlactating Holstein cows and beef heifers in Canada compared three commercially available gonadorelin formulations (Cystorelin, Fertagyl, and Factrel) at 100 micrograms intramuscularly, measuring luteinizing hormone via blood samples collected at multiple timepoints from 0 to 6 hours and monitoring ovulation by ultrasonography. The authors reported that mean and peak plasma LH concentrations were higher in cows treated with Cystorelin, and that the proportion of dominant follicles that ovulated was higher with Cystorelin than with Fertagyl or Factrel in Holstein cows (18/19, 11/19, and 4/7 respectively), though not significantly different among products in beef heifers (6/10, 6/10, and 4/10). No significant differences were found in the interval to next follicular wave emergence.
Abstract
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.
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