145 Comparison of single to multiple injections of follicle-stimulating hormone before ovum pickup in Holstein heifers: Oocyte recovery and embryo production

Abstract

The demand for invitro-produced embryos from heifers with high genetic merit has increased over time. Synchronization and stimulation of follicular growth before ovum pickup (OPU) has been used to improve oocyte quality and, consequently, embryo production. Multiple injections involve extra labour and stress for both personnel and cattle. The release of FSH can be prolonged by using 0.5% hyaluronan (HA) as a diluent, allowing a decrease in the number of injections. The objective of this study was to compare oocyte recovery and embryo production between single or multiple injections of FSH before OPU of Holstein heifers. During April and May 2020, 20 Holstein heifers (8 to 15 mo old) from Ruann Dairy (Riverdale, CA) were randomly divided and submitted to two different treatments (crossover design). Gonadotrophin-releasing hormone (GnRH; Fertagyl®, Merck, 129µg, IM) was given to synchronize the follicular wave emergence. Treatment 1×FSH consisted of a single intramuscular (IM) injection of 100mg of FSH (Folltropin®, Vetoquinol) 36h after GnRH. The FSH consisted of a 2.5-mL injection of 400mg of FSH diluted in 10mL of 0.5% HA. OPU was performed 48 to 50h after FSH. Treatment 5×FSH consisted of 100mg of FSH divided into 5 equal IM injections (10-14h intervals) 36h after GnRH. The FSH consisted of 5×1-mL injections of 400mg of FSH in 20mL of saline. OPU was performed 18 to 20h after the last FSH injection. All donors received both treatments at a 14-day interval and the recovered oocytes were fertilized with the same sexed female-sorted semen in both rounds. OPU, oocyte classification, IVM, IVF, and culture (IVC) were performed as described by Demetrio et al. (2020 Anim. Reprod. 17, e20200053). All oocytes went into IVM, except for degenerated oocytes. The number of 4-cell (or more) embryos on Day 3 of IVC divided by the number of oocytes in IVC after IVF is defined as the cleavage rate. The number of blastocysts (early to hatched) on Day 7 of IVP divided by the number of oocytes in IVC after IVF is defined as the blastocyst rate. Poisson-normal (count data) and Logistic-normal (proportion data) models were used to analyse the data. Treatment, donor (random effect), and sire were included in the models. The results are summarized in Table 1. There were no differences between the two treatments on the number of oocytes recovered per OPU (total and grade 1 and 2), percentage of grade 1 and 2 oocytes, cleavage rate, blastocyst rate and number of embryos (total and grade 1). Oocyte recovery and embryo production are highly donor dependent. Stimulation of the follicular growth before OPU with one single injection of FSH diluted in 0.5% HA 36h after GnRH can be efficiently used for IVP in Holstein heifers, without decreasing the number of oocytes recovered and/or embryos produced with the advantage of reducing labour and stress of handling cattle. Table 1. Number and quality of oocytes and cleavage and blastocyst rates Treatment OPU Oocytes per donor Grade 1 and 2 oocytes (%) Cleavage rate (%) Blastocyst rate (%) Total embryos per OPU Grade 1 embryos per OPU 1×FSH 20 17.0 45.7 84 39.8 6.2 3.8 5×FSH 20 19.9 46.5 82 35.6 6.3 4.0