Lecirelin-cloprostenol: A single-dose compounding formulation for ovulation induction in beef cows.
GPG may improve ovulatory synchrony in cattle, but its impact on pregnancy rates is marginal and not statistically significant in larger studies.
Where it sits
this study against the rest of the gonadorelin (gnrh) corpusSummary and findings
The study evaluated the effects of a Lecirelin-Cloprostenol combination on ovulation induction in Nelore cattle subjected to timed artificial insemination (TAI). Eight experiments were conducted with varying sample sizes, and the results indicated that GPG induced earlier ovulation and reduced the dispersion of ovulation timing compared to GnRH alone. However, the effects on pregnancy per artificial insemination (P/AI) were marginal.
Abstract
While GnRH induces the preovulatory LH surge, PGF2α triggers luteolysis and uterine contraction. Therefore, Lecirelin-Cloprostenol combination given at the end of the TAI protocol may improve fertility in cows. Eight studies evaluated a novel Lecirelin-Cloprostenol (GPG) fixed-dose combination for ovulation and fertility in Nelore cattle subjected to timed artificial insemination (TAI) protocols. Initial experiments (Exp. 1, n = 28) showed GPG and GnRH induced earlier ovulation than PGF. In Exp. 2 (n = 25) and Exp. 4 (n = 17), the GPG protocol reduced the dispersion of ovulation timing compared to GnRH alone (Bartlett's test, P < 0.05). In Exp. 3, the GPG group had lower intrafollicular estradiol (P = 0.04) and higher PTGS2 gene expression (P = 0.05) compared to the GnRH group. Fertility outcomes varied: GPG tended (P = 0.1) to increase pregnancy per artificial insemination (P/AI) in postpartum cows (Exp. 5, n = 326) and improved ovulation rates when estradiol cypionate (EC) was used (Exp. 6, n = 17). While a large field study (Exp. 7, n = 948) showed no overall P/AI difference when the GPG treatment was given following estradiol cypionate. Finally, GPG and GnRH had similar P/AI (P = 0.3) in non-estrus cows (Exp. 8, n = 1692) compared to GnRH. In conclusion, GPG upregulated PTGS2 expression and decreased intrafollicular E2 concentrations in the ovulatory follicle relative to GnRH, providing a mechanistic basis for the improved ovulatory synchrony observed in GPG-treated cows. While the GPG formulation consistently reduced the dispersion of ovulation timing across experiments, effects on P/AI were marginal in the present study.
Background
This paper addresses the role of GnRH and PGF2α in ovulation and fertility in cattle, specifically examining a novel Lecirelin-Cloprostenol combination. Prior research established that GnRH induces the preovulatory LH surge, while PGF2α triggers luteolysis. This study is significant as it explores a new fixed-dose combination that may enhance fertility outcomes in cattle subjected to timed artificial insemination protocols.
Methods
The study comprised eight experiments with varying populations of Nelore cattle subjected to timed artificial insemination protocols. Sample sizes ranged from 17 to 1692 across different experiments, with doses of Lecirelin-Cloprostenol evaluated. The primary outcome measures included ovulation timing and pregnancy per artificial insemination.
Results
The primary endpoint indicated that GPG reduced the dispersion of ovulation timing compared to GnRH alone (Bartlett's test, P<0.05), n=25. Additionally, the GPG group exhibited lower intrafollicular estradiol (P=0.04) and higher PTGS2 gene expression (P=0.05) compared to the GnRH group. However, the overall effects on pregnancy per artificial insemination were marginal, with no significant differences observed in larger studies.
Interpretation
The findings suggest that while GPG may improve ovulatory synchrony, the clinical significance of the effects on pregnancy rates is limited. Previous literature supports the role of GnRH in ovulation induction, but the marginal improvements observed with GPG raise questions about its practical application. Confounding factors such as varying sample sizes and the lack of significant P/AI differences in larger studies may limit the conclusions drawn from this research.
Key findings
- GPG and GnRH induced earlier ovulation than PGF, n=28.
- GPG reduced the dispersion of ovulation timing compared to GnRH alone (Bartlett's test, P<0.05), n=25.
- GPG group had lower intrafollicular estradiol compared to GnRH group (P=0.04).
- GPG tended to increase pregnancy per artificial insemination (P/AI) in postpartum cows (P=0.1), n=326.
- No overall P/AI difference when GPG treatment was given following estradiol cypionate in a large field study (n=948).
- GPG and GnRH had similar P/AI in non-estrus cows (P=0.3), n=1692.
Limitations
- small n in some experiments
- effects on P/AI were marginal
- varying sample sizes across experiments
- no significant P/AI difference in large field study, n=948
- single-site study may limit generalizability