Phenylbutazone treatment of mares does not reduce embryo production via intracytoplasmic sperm injection.

Overview

• This study investigates whether treating mares with phenylbutazone, a non-steroidal anti-inflammatory drug, affects the success of embryo production using intracytoplasmic sperm injection (ICSI).
• The research found that different methods of administering phenylbutazone do not reduce the rates of oocyte recovery, maturation, cleavage, or blastocyst formation during the in vitro embryo production process.

Background and Purpose

• Intracytoplasmic sperm injection (ICSI) is commonly used to produce equine embryos in clinical practice.
• A prior study suggested that treating mares with phenylbutazone paste might significantly reduce the production of blastocysts after ICSI.
• This study aimed to evaluate the impact of different phenylbutazone administration methods (oral liquid, oral paste, intravenous) on embryo production outcomes from recovered oocytes in mares.

Study Design and Methods

• Study 1: Conducted between July 29 and September 18, 2024.
• 14 mares were used.
• Mares received oral liquid phenylbutazone once daily for 10 days or no treatment (control).
• On the last treatment day, all mares underwent transvaginal follicle aspiration (TVA) to recover oocytes.
• Recovered oocytes were matured in vitro and used in ICSI to produce embryos.
• Mares were then switched to the alternate treatment and TVA and ICSI were repeated to serve as their own controls.
• Study 2: Conducted from October 29 to December 25, 2024.
• 15 mares participated.
• Mares received intravenous (IV) liquid phenylbutazone, oral phenylbutazone paste, or no treatment in a 3-way crossover design.
• After each treatment session, mares rotated through the other treatments so each mare experienced all three regimens.
• Oocytes were again collected by TVA, matured, and subjected to ICSI to assess embryo production.

Results

• Study 1 Findings:
• Oocyte recovery rates were similar between the oral liquid phenylbutazone group and the control group.
• Maturation rates of recovered oocytes did not differ significantly between treated and untreated mares.
• Cleavage rates after ICSI and blastocyst formation per injected oocyte were comparable (49% in treated mares vs. 46% in controls).
• Study 2 Findings:
• No significant difference in oocyte recovery, maturation, cleavage, or blastocyst rates was observed among the IV phenylbutazone group, oral paste group, and control group.
• Blastocyst rates were 42% for IV phenylbutazone, 30% for oral paste, and 42% for control, with no statistical difference.

Conclusions

• Administration of phenylbutazone to mares, regardless of method (oral liquid, oral paste, intravenous), does not negatively impact in vitro embryo production via ICSI.
• Mares can safely remain on phenylbutazone treatment for pain relief or comfort during the processes of transvaginal follicle aspiration and ICSI without compromising embryo production outcomes.
• This suggests that concerns arising from previous studies about phenylbutazone reducing blastocyst rates may depend on factors not confirmed here, such as dosage, formulation, or other variables.

Implications for Equine Reproductive Medicine

• Phenylbutazone remains a useful pharmacological option to manage discomfort or inflammation in mares undergoing reproductive procedures.
• The safety of phenylbutazone during critical reproductive procedures supports its continued clinical use without fear of reducing embryo production efficiency via ICSI.
• Further studies could explore any long-term effects or evaluate other NSAIDs, but current data provide reassurance for veterinarians and breeders using phenylbutazone in equine ICSI protocols.