Fertility of conventional and of sex-sorted stallion sperm using SexedULTRA™ Genesis III technology

Abstract

Sex-sorted (SS) bull sperm has been adopted worldwide due to the economic benefits and acceptable fertility (Crites BR et. al Theriogenology 118:126-129, 2018). Previous (15-20 years ago) studies using SS stallion sperm resulted in lower fertility when mares were bred with SS compared to non-sorted (NS) stallion sperm whether fresh (Buchanan BR Theriogenology 53:1309-1321, 2000); cool-stored (Lindsey et al. An. Reprod. Sc.85:125-130 2005), or frozen/thawed SS semen (Clulow et al. An. Reprod. Sc. 108:287-297, 2008). Recently, STgenetics, Navasota, TX, USA, a company dedicated to commercial SS semen, has developed a sperm sorter technology (SexedULTRA™ Genesis III) that reduces sorting time, increases the speed and efficiency of SS and reduces the amount of sperm damage (Gonzalez-Marin C. et al Theriogenology 114:40-45, 2018). In the present study, sperm quality (total motility, viability, and DNA damage) and fertility of mares bred with 40 million non-sorted (NS) or sex-sorted (SS) sperm were compared. Semen from 3 sexually active fertile stallions was diluted 1:3-1:4 in BotuSemen Gold supplemented with 0.06 mg/ml of Hoechst 33342 stain and cooled to 8°C for 18 h. Semen was then warmed to room temperature and centrifuged through a colloid suspension (EquiPure). The sperm pellet was resuspended to 250-300 million/ml using a proprietary chemically defined medium (ST Equiship,STgenetics, Navasota, TX) and transported at ∼20°C for approximately 45 min to the sorting facility. When 40 million SS were harvested (approx 2-3h) SS or NS semen [LCC1] [LCC2] were loaded in 4-5 0.5 mL straws and inseminated (1x/cycle) using a deep-horn artificial insemination technique. A total of 17, 8-21 year old mares were bred on 65 cycles. When mares had uterine edema of 3/5 and a dominant follicle of > 35 mm, 1 mg of deslorelin acetate (Sucromate®) was administered IM. Mares were inseminated ∼24h after deslorelin administration and examined for ovulation 12-18h post AI. Seven to 8d post-ovulation non-surgical embryo recovery was performed. Total sperm motility (86%) and viability (84%) were higher and DNA damage was lower (4%) in SS compared to NS sperm (78, 82,12%) (p<0.05). Embryo recovery rates were similar for NS (46.6%) compared to SS sperm (40%) (p>0.05). The expected sex of all embryos was correctly identified by PCR using the presence or absence of the SRY gene (Choi YH et al, Reproduction 140: 893 – 902, 2010). Overall, sperm quality of SS sperm was similar or higher to that of NS stallion sperm while embryo recovery rates were similar. Further studies are underway to validate this technology on a commercial scale.