ABSTRACT.- Pregnancy rates following embryo transfer (ET) in cattle may be influenced by transient inflammatory responses triggered during the procedure. The objective of this study was to evaluate the effect of tolfenamic acid (TA), a nonsteroidal anti-inflammatory drug (NSAID), on pregnancy rates in embryo-recipient females. A total of 1431 recipients (367 heifers and 1064 cows) were enrolled in 34 ET programs conducted on 24 commercial farms in Uruguay, using either in vivo-derived or in vitro-produced embryos, fresh or frozen. At the time of ET, recipients were randomly assigned to either a treatment group receiving a single dose of TA (2 mg/kg intramuscularly) or a control group receiving no treatment. Pregnancy diagnosis was performed between days 35 and 60 post-T via transrectal ultrasonography. No significant difference was attained in overall pregnancy rates between TAtreated (53.7 %, 389/725) and untreated (49.7 %, 351/706) recipients (P = 0.13). However, in specific subgroups TA treatment increased pregnancy rates, reaching statistical significance in heifers (P = 0.04) and a tendency in animals with a body condition score below 3.0 (1?5 scale; P = 0.07) and recipients with smaller corpus luteum size (P = 0.09). Additionally, NSAID treatment improved pregnancy rates in recipients receiving in vitro-produced embryos at the morula stage (P = 0.05) but not at the early to expanded blastocyst stages (P = NS). In conclusion, we suggest that TA may provide reproductive benefits under specific ET situations, particularly in heifers and recipients with physiological or embryonic conditions commonly associated with reduced
fertility. © 2025 The Authors. Published by Elsevier Inc.