Systematic review and meta-analysis of fertility outcome following in vivo insemination with sex-sorted semen in sheep

Abstract

Background: Sex-sorted semen (SS) offers economic benefits to sheep producers, but lower fertility outcome (FO), defined as probability of pregnancy, pregnancy rate or lambing rate, than that following conventional semen (CS) artificial insemination (AI) may limit its use.

Objectives: To systematically review the literature, and analyse factors associated with FO following AI in sheep using SS vs CS.

Methods: Available literature was searched using the PRISMA guidelines, resulting in 11 studies with 14 experiments that were reviewed. From these, information from 70 study cohorts representing 13 experiments was used to conduct a meta-analysis which confirmed that FOs for SS and CS AI were 37% (95% CI = 31–43%) and 52% (95% CI = 45–59%), respectively (p < 0.01).

Results: FO improved over time, with FO following SS and CS AI improving at the same rate over the period investigated (1997-2022). In a subgroup analysis, five factors were identified that potentially decrease the FO after SS AI disproportionately. These were sperm dose ≤ 4 × 106 spermatozoa, semen preservation (fresh vs frozen-thawed), oestrus synchronisation using an intravaginal sponge (vs a controlled internal drug release device), presence of gonadotropin-releasing hormone in the synchronisation protocol, and absence of biostimulation using a teaser ram. In a random-effects model analysis, an interaction between sperm dose and SS vs CS, and semen preservation were independent predictors of FO after adjusting for the effect of timing of insemination.

Conclusion: FO following insemination with SS is 15% lower than that of CS, which can be narrowed by increasing the semen dose for SS inseminations and improving the synchronisation of ovulation with the timing of insemination.