Dominant follicle removal prior to superovulation

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Published on: April 6, 2020

Taylor Mittleider, a Brianna Price, a John Gibbons, a Jason Anton b
a College of Veterinary Medicine, Lincoln Memorial University, Harrogate, TN, b Ovaflo Genetics, Tahlequah, OK

Introduction: Superovulation and embryo collection and transfer enables cattle producers to reach reproductive, financial, and genetic goals. Although knowledge of follicular development has improved, the number of transferable embryos per collection has not, leading to a high degree of unpredictability. Follicular stimulating hormone (FSH) is a major cost of embryo transfer, and administration must occur coincidentally with an endogenous FSH surge for effective superovulation and embryo recovery, which has not improved substantially in many years, possibly due to suboptimal timing of FSH delivery (Adams, 1992). A major source of variability in the superovulatory response in cattle is the status of ovarian follicles at the time of initiation of FSH treatments (Mapletoft, Steward, & Adams, 2002). Following dominant follicle ablation, an FSH surge and associated follicular wave can be predicted and managed, which may lead to more consistent embryo collections and more transferable embryos (Crowe, 2013). The purpose of this field trial was to evaluate dominant follicle ablation prior to superovulation with a minimal dose of FSH.

Methods: Cycling beef cattle, at random stages of the estrous cycle , were subjected to transvaginal ultrasound-guided aspiration of all follicles (> 5 mm). Following aspiration, PGF2a (25 mg) was administered and a CIDR was placed. Approximately 48 hours later, Folltropin-V administration began and was given twice daily (am and pm) for 4 days. On the third day of FSH administration, PGF2a was given again and the CIDRs were removed that evening. Cattle were inseminated at estrus. One week later, embryos were collected and corpora lutea (CL) were counted using transrectal ultrasonography. All data, both pre-recovery and day of recovery, were analyzed statistically using ANOVA.

Results: Neither the number of follicles ablated, nor the diameter of the ablated follicles had any statistical effect on embryo recovery; however, as indicated in Table 1, cattle (n = 24) with a CL < 22 mm at ablation, tended (P = 0.086) to produce fewer transferable quality embryos (mean ± SEM; 5.8 ± 0.7) than cattle (n = 26) with a CL ≥ 22 mm (8.1 ± 1.1) at ablation.

Cattle (n = 35) given ≥ 10 mls of FSH had a similar number of; total ova (11.3 ± 1.3), transferable embryos (6.2 ± 0.9), and CL (14.2 ± 0.9) compared to cattle (n = 28) given < 10 mls of FSH (12.3 ± 1.1, 6.3 ± 0.6, 15.1 ± 1.0, respectively). This approach also facilitated acceptable results from consecutive embryo recoveries (Figure 1).


Conclusion: Dominant follicle removal prior to superovulation, required less exogenous FSH to achieve acceptable embryo recovery results. These results indicated that ablation of follicles (> 5mm) in cycling mid-diestrus beef cattle, prior to initiation of superovulation may yield more consistent embryo production perhaps due to a more tightly synchronized engineered follicular wave. Further characterization of the dynamics of this follicular wave may facilitate more consistent superovulation results and reduce costs.

References:
Adams GP, Matteri RL, Kastelic JP, Ko JC, Ginther OJ. Association between surges of follicle-stimulating hormone and the emergence of follicular waves in heifers. Journal of Reproduction Fertility, 1992; 94(1):177-188.

Crowe MA, Mullen MP. Relative roles of FSH and LH in stimulation of effective follicular response in cattle. Intech Open Access, 2013; http://dx.doi.org/10.5772/50272.

Mapletoft, R. J., Steward, K. B., & Adams, G. P. (2002). Recent advances in the superovulation in cattle. Reproduction, nutrition, development, 42(6), 601–611. https://doi.org/10.1051/rnd:2002046

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