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

Objective: Production of embryos via intracytoplasmic sperm injection (ICSI) is a common clinical procedure in equine practice. A recent study indicates that treatment of mares with phenylbutazone paste significantly lowers blastocyst production after ICSI of recovered oocytes. The current study was conducted to determine the effect of different methods of phenylbutazone administration on in vitro embryo production of recovered oocytes in mares.

Methods: In study 1 (July 29 through September 18, 2024), 14 mares received either oral liquid phenylbutazone once daily for 10 days or no treatment. On the last day of treatment, all mares underwent transvaginal follicle aspiration (TVA) and recovered oocytes were matured and subjected to ICSI. The mares were then crossed over into the alternate treatment, and TVA and ICSI were repeated. In study 2 (October 29 through December 25, 2024), 15 mares received liquid phenylbutazone IV, phenylbutazone paste orally, or no treatment in a 3-way crossover design. After each session, the groups were rotated so that each mare received each of the 3 treatments.

Results: In study 1, oocyte recovery rates, maturation rates, cleavage rates, and blastocyst rates per injected oocyte (oral liquid phenylbutazone group, 49%; control group, 46%) did not differ significantly between the 2 treatments. In study 2, oocyte recovery rates, maturation rates, cleavage rates, and blastocyst rates (IV phenylbutazone group, 42%; oral phenylbutazone paste group, 30%; control group, 42%) did not differ significantly between treatments.

Conclusions: Administration of phenylbutazone to mares, as performed in this study, did not have an effect on in vitro embryo production.

Clinical relevance: Mares that are undergoing TVA and ICSI can remain on phenylbutazone for comfort and quality of life.