Single-dose FSH protocol with 48- or 72-h coasting periods as simplified alternatives for in vitro embryo production in Angus oocyte donor cows.

The aim of the present study was to evaluate different superstimulation protocols prior to follicular aspiration and to compare coasting periods on superstimulatory response and in vitro embryo production (IVP) in Bos taurus cows. Donor cows were randomly assigned to one of four treatment groups in a crossover design repeated across four replicates: (1) a negative control (no FSH), (2) a multiple-injection FSH protocol, (3) a single-dose FSH diluted in hyaluronic acid with a 48 h coasting period (MAP48), and (4) a single-dose FSH diluted in hyaluronic acid with a 72 h coasting period (MAP72). In all FSH-treated groups, cows received a total dose of 160 mg of FSH. To ensure that ovum pick-up (OPU) was performed on the same chronological day in all four groups, the initiation of progesterone, GnRH, and FSH treatment in the MAP48 group was delayed by one day, thereby achieving a shorter coasting period without altering the timing of OPU. Ovum pick-up was performed simultaneously in all groups, and recovered cumulus-oocyte complexes (COCs) were evaluated and cultured, followed by in vitro fertilization and culture of presumptive zygotes. Superstimulation with FSH increased the number of viable COC and tended to increase blastocyst production compared with untreated controls. No differences were observed in COC recovery, embryo production, or blastocyst production rates between the multiple FSH protocol and the single-dose (MAP48 or MAP72) protocols, nor between the two coasting periods. Day 7 blastocysts were further analyzed to evaluate embryo quality, including relative gene expression of inner cell mass and trophectoderm markers and total and CDX2-positive cell number. No differences were detected among treatments for any of these variables, suggesting that the day of oocyte collection per se does not affect embryo quality when coasting periods are within the studied range. In conclusion, single-dose protocols of FSH diluted in hyaluronic acid were as effective as multiple FSH injections for IVP in beef cows, and shortening the coasting period from 72 to 48 h did not compromise embryo yield or quality.