The effect of sperm and cryoprotectant concentration on the freezing success of sex sorted ram sperm for in vitro fertilization

Cysteine supplementation pre-freeze and post-thaw improves integrity and reduces oxidative stress in cryopreserved ram spermatozoa

Cryopreserved ram sperm is highly sensitive to oxidative stress by reactive oxygen species (ROS) which impair sperm function and integrity. Antioxidants such as cysteine can mitigate the effect of ROS, although the optimal concentration or timing of supplementation is unknown. This study aimed to determine the effect of concentration and timing of cysteine supplementation on the integrity and function of cryopreserved ram spermatozoa. Nine ejaculates were collected from three Texel rams then cryopreserved and supplemented with cysteine (0, 0.5, or 1.0 mg/mL) added pre-freeze (PF), post-thaw (PT) or pre-freeze and post-thaw (PF + PT) generating seven treatments: 1) control 0 mg/mL, 2) PF 0.5 mg/mL, 3) PF 1 mg/mL, 4) PT 0.5 mg/mL, 5), PT 1.0 mg/mL, 6) PF + PT 0.5 mg/mL and 7) PF + PT 1.0 mg/mL. Sperm motility, viability, acrosome integrity, ROS production and penetrability through artificial cervical mucus were assessed post-thaw. Cysteine supplementation reduced ROS production which thereby improved spermatozoa motility, viability, acrosome integrity and penetrability (p < 0.001) Sperm integrity for all parameters was greatest in spermatozoa treated PF + PT with 1.0 mg/mL cysteine, although treatment pre-freeze or post-thaw also improved integrity beyond the control. This study has identified that 1.0 mg/mL cysteine is most beneficial and has highlighted the importance of preventing oxidative stress in spermatozoa post-thaw. These finding can help to mitigate the detrimental effect of cryopreservation on spermatozoa and aid the development of cryopreservation protocols in sheep.

Sex selection of sperm in farm animals: status report and developmental prospects

Pre-selection of spermatozoa based on the relative DNA difference between X- and Y-chromosome bearing populations by flow cytometry is an established method that has been introduced into commercial cattle production. Although several important improvements have increased the sort efficiency, the fertilising ability of sexed spermatozoa based on offspring per insemination is still behind farmers' expectations. The main stress factors, especially on mitochondria, that reduce the lifespan of spermatozoa are described, and new technical as well as biological solutions to maintain the natural sperm integrity and to increase the sorting efficiency are discussed. Among these methods are the identification of Y-chromosome bearing spermatozoa by bi-functionalised gold nanoparticles and triplex hybridisationin vivoas well as new laser-controlled deflection system that replaces the deflection of spermatozoa in the electrostatic field. Additionally, as well as a new nonsurgical transfer system of spermatozoa into the oviduct of cows has been developed and allows a significant reduction of spermatozoa per transfer. Altogether, the improvements made in the recent years will allow a broader use of sex-sorted spermatozoa even in those species that require more cells than cows and sheep.

Quantitative mRNA expression in ovine blastocysts produced from X- and Y-chromosome bearing sperm, both in vitro and in vivo

Artificial insemination (AI) of sex-sorted sperm results in decreased fertility, compared with non-sorted sperm, in most species. However, this has not been the case in sheep, where the low-dose AI of sex-sorted ram sperm produced similar, if not superior, fertility to non-sorted controls. The aim of the present study was to determine the impact of sex-sorting technology on ovine embryo gene expression following embryo production in vivo and in vitro. After semen collection, ejaculates were split and either sex-sorted by flow cytometry and frozen, or diluted and frozen. Embryos were produced in vivo by inseminating superovulated ewes with either X- or Y-chromosome enriched sperm, or non-sorted control sperm, and collected by uterine flushing on Day 6 after AI. Embryos were produced in vitro using the same sperm treatments and cultured in vitro for 6 d. The relative abundance of selected gene transcripts was measured in high-grade blastocysts, defined by morphological assessment, using RT-qPCR. The mRNA expression of DNMT3A and SUV39H1 was upregulated in embryos cultured in vitro, compared to those cultured in vivo (DNMT3A: 3.61 ± 1.08 vs 1.99 ± 0.15; SUV39H1: 1.88 ± 0.11 vs 0.88 ± 0.07; mean ± SEM; P < 0.05). Both G6PD and SLC2A3 transcripts were reduced in embryos produced from sex-sorted sperm, in vivo (SLC2A3: 0.23 ± 0.03 vs 0.64 ± 0.10; G6PD: 0.32 ± 0.04 vs 1.01 ± 0.16; P < 0.05). The expression of DNMT3A was up-regulated in male (3.85 ± 0.31), compared to female embryos (2.34 ± 0.15; P < 0.05). This study contributes to the growing body of evidence citing aberrant patterns of gene expression resulting from in vitro culture. Whereas the process of sex-sorting altered the expression of several of the genes examined, no effect on embryo development was detected.