Sustainable animal production: exploring the benefits of sperm sexing technologies in addressing critical industry challenges

The sex of the animals is of paramount importance in many animal production systems. This is particularly evident in the production of milk or in breeding programs focused on the production of female animals. In some cases, slaughter or euthanasia of animals of the unwanted sex becomes the only solution, highlighting ethical and economic concerns. As global demand for food continues to rise, the importance of addressing these issues becomes more evident. Reproductive technologies, such as sperm sexing techniques, may hold the key to addressing both animal welfare and the sustainability of animal production. The use of semen enriched with sperm capable of producing offspring of the desired sex can serve as a valuable tool for producers to exert greater control over production outcomes, not only helping to mitigate welfare issues related to the unnecessary premature death of unwanted offspring but also providing a possible ally in the face of stricter animal welfare guidelines. In addition, sexed semen can also contribute to financial gains and reduce greenhouse gas emissions and food waste associated with the less profitable part of the herd. This paper explores the positive impacts that sperm sexing can have on animal welfare, economy, and environment. It also discusses currently available options and strategies for more successful implementation of sexed semen. Partnerships between companies and scientists will be essential to find innovative ways to adapt current production systems and develop sperm sexing technologies that apply to most livestock industries.

Pregnancy and offspring sex ratio following insemination with SexedULTRA and conventional semen in cows in a commercial beef operation

Pregnancy rate per AI (PR/AI) and breeding season pregnancy rates between insemination with sexed semen (SS; at 18 hr after the onset of oestrus) and conventional semen (CS; at 12 hr after the onset of oestrus,) and offspring gender ratio between two groups were compared. Angus cross cows (n = 686, during 2019 and 2020 breeding seasons) were oestrus-synchronized using Select-Synch + CIDR protocol and were observed thrice daily for oestrus until 72 hr after PGF2α administration. Cows expressed oestrus (n = 513) were inseminated with either SS (n = 246; SexedULTRA 4M™; y chromosome-bearing sperm) or CS (n = 267). Cows (n = 173) that failed to express oestrus at 72 hr after PGF2α received 100 μg of GnRH and CS insemination concomitantly. Two weeks later, cows were penned with natural service sires (bull:cow ratio 1:25) for 45 days. Pregnancy was diagnosed 30 days after bull removal. Calves' gender was determined at birth. For cows that expressed oestrus, PR/AI did not differ (p > .1) between SS (65.0%) and CS (66.7%) groups. The overall PR/AI differed (p < .05) between SS (65.0%) and CS (56.4%) groups. The natural service PR differed (p < .001) but breeding season PR (p > .05) did not differ between SS vs. CS groups. Bull:heifer gender ratio following AI was 88:12 and 52:48 for SS and CS groups, respectively, with an overall 66:34 ratio. Bull:heifer gender ratio for the two breeding seasons was 79:21 and 52:48 for SS and CS groups, respectively, with an overall 62:38 ratio. In conclusion, the fertility of SS insemination at 18 hr after onset of oestrus was 97% of CS insemination at 12 hr after onset of oestrus. Though breeding season pregnancy did not differ between SS and groups, preferred calf gender was 25 percentage points greater for SS over CS application. The gender accuracy was 88%.

Small ruminant SexedULTRA™ sperm sex-sorting: Status report and recent developments

Flow cytometry sperm sex-sorting based on the relative DNA difference between X- and Y-chromosome bearing populations is an established method that has allowed the production of pre-sexed offspring in a multitude of species and has been a commercial success in cattle production for the past twenty years. Several improvements to the technology and the processing methods have increased the sorting efficiency of ejaculates and the post-thaw quality of sex-sorted sperm, allowing for the fertility gap between conventional (non-sorted) and SexedULTRA™ sex-sorted sperm to be bridged. Small ruminant industries are now progressively testing sex-sorted sperm for application in their specific niches and environments. A review of the key advances and the recent developments in caprine, ovine and cervine sperm sex-sorting technology are described in this publication.

Effect of sex-sorting and cryopreservation on the post-thaw sperm quality of Iberian red deer spermatozoa

This study investigated the effect of sex-sorting and cryopreservation on post-thaw characteristics and fertility of red deer (Cervus elaphus) sperm for the first time. Semen was collected by electroejaculation from 10 mature stags during the breeding season, and each ejaculate split into four experimental groups: Bulk sorted spermatozoa, sorted but not sexed (BSS); sorted high purity X-spermatozoa (XSS); sorted high purity Y-spermatozoa (YSS); and, control non-sorted spermatozoa (NS). Following, all samples were frozen over liquid nitrogen. Two straws per stag and sample type were analyzed immediately post-thaw and following a 2-h incubation period at 37 °C. Post-thaw total motility (TM) as assessed by CASA was not different (P < 0.05) among NS, BSS and YSS sperm. For XSS, post-thaw TM was lower (39%, P < 0.05) than that for NS (54%) or BSS (50%), but similar (P > 0.05) to that of YSS (47%) sperm. The percentage of apoptotic spermatozoa as assessed by PI/YO-PRO-1 and flow cytometry analysis, was higher (17%, P ≤ 0.05) for XSS sperm than NS (12%), BSS (13%) and YSS (14%) sperm. Following incubation there were no differences (P > 0.05) in TM or percent apoptosis among treatments. Post-thaw chromatin stability calculated as the DNA fragmentation index (%DFI) was similar among treatments; following incubation %DFI increased in all except YSS, which displayed the lowest value (P < 0.05). Artificial insemination of synchronized hinds yielded 44, 52 and 62% delivery rates for YSS, NS and standard frozen-thawed sperm, respectively (P < 0.05). Notably, 93 and 55% of fawns born were males for the YSS and NS spermatozoa, respectively (P < 0.05). In summary, Y-sorted sperm displayed acceptable post-thaw sperm evaluation parameters and the expected offspring sex ratio. More studies are needed to understand the source of sperm damage that may compromise the fertility of Y-sorted red deer sperm.

Assisted reproduction with gametes and embryos: what research is needed and fundable?

Principles for selecting future research projects include interests of investigators, fundability, potential applications, ethical considerations, being able to formulate testable hypotheses and choosing the best models, including selection of the most appropriate species. The following 10 areas of assisted reproduction seem especially appropriate for further research: efficacious capacitation of bovine spermatozoa in vitro; improved in vitro bovine oocyte maturation; decreasing variability and increasing efficacy of bovine superovulation; improved fertility of sexed semen; improving equine IVF; improving cryopreservation of rooster spermatozoa; understanding differences between males in success of sperm cryopreservation and reasons for success in competitive fertilisation; mechanisms of reprogramming somatic cell nuclei after nuclear transfer; regulation of differentiation of ovarian primordial follicles; and means by which spermatozoa maintain fertility during storage in the epididymis. Issues are species specific for several of these topics, in most cases because the biology is species specific.

Birth of kids after artificial insemination with sex-sorted, frozen-thawed goat spermatozoa

Successful sex-sorting of goat spermatozoa and subsequent birth of pre-sexed kids have yet to be reported. As such, a series of experiments were conducted to develop protocols for sperm-sorting (using a modified flow cytometer, MoFlo SX(®) ) and cryopreservation of goat spermatozoa. Saanen goat spermatozoa (n = 2 males) were (i) collected into Salamon's or Tris catch media post-sorting and (ii) frozen in Tris-citrate-glucose media supplemented with 5, 10 or 20% egg yolk in (iii) 0.25 ml pellets on dry ice or 0.25 ml straws in a controlled-rate freezer. Post-sort and post-thaw sperm quality were assessed by motility (CASA), viability and acrosome integrity (PI/FITC-PNA). Sex-sorted goat spermatozoa frozen in pellets displayed significantly higher post-thaw motility and viability than spermatozoa frozen in straws. Catch media and differing egg yolk concentration had no effect on the sperm parameters tested. The in vitro and in vivo fertility of sex-sorted goat spermatozoa produced with this optimum protocol were then tested by means of a heterologous ova binding assay and intrauterine artificial insemination of Saanen goat does, respectively. Sex-sorted goat spermatozoa bound to sheep ova zona pellucidae in similar numbers (p > 0.05) to non-sorted goat spermatozoa, non-sorted ram spermatozoa and sex-sorted ram spermatozoa. Following intrauterine artificial insemination with sex-sorted spermatozoa, 38% (5/13) of does kidded with 83% (3/5) of kids being of the expected sex. Does inseminated with non-sorted spermatozoa achieved a 50% (3/6) kidding rate and a sex ratio of 3 : 1 (F : M). This study demonstrates for the first time that goat spermatozoa can be sex-sorted by flow cytometry, successfully frozen and used to produce pre-sexed kids.

Reducing sperm concentration is critical to limiting the oxidative stress challenge in liquid bull semen

Because of the short breeding season, the use of liquid bull semen is a viable option in seasonal grass-based dairy systems such as Ireland. Currently in Ireland, liquid bull semen contains approximately 5 million sperm per insemination dose and is used within 2.5d of collection. The hypothesis of this study was that reducing the sperm number per insemination dose would enable bull sperm to be stored for longer. Semen was collected at a commercial AI center and diluted to 1 (T1), 2 (T2), 3 (T3), 4 (T4), and 5 (T5) million sperm per 0.25-mL dose in caprogen diluent. On d 0.25 (6 h postcollection), 1, 2, 3, 4, and 5 postcollection, viability, oxidative stress, and mitochondrial activity were assessed using flow cytometry and the fluorescent probes propidium iodide, CM-H2DCFDA, and rhodamine 123, respectively. On the same days, glucose consumption, total antioxidant capacity, and progressive linear motility were assessed. We observed an effect of day and treatment on sperm cell viability, with the highest percentage live found in T 0005 and the lowest in T 0025 on all days. Oxidative stress in live sperm increased with duration of storage and was affected by treatment, being highest in T 0025 and lowest in T 0005 on all days (d 5: 56.4±2.76% and 28.8±1.22%, respectively; mean ± SEM). Both the total antioxidant capacity and percentage of live sperm positive for rhodamine 123 were unaffected by treatment. The concentration of glucose in caprogen declined with time and was lowest in T 0025 and highest in T 0005 on d 5. In conclusion, higher concentrations of sperm have detrimental effects on sperm cell viability and increase oxidative stress but have no effect on the mitochondrial activity of sperm.

Development and evaluation of deep intra-uterine artificial insemination using cryopreserved sexed spermatozoa in bottlenose dolphins (Tursiops truncatus)

Since its development in bottlenose dolphins, widespread application of AI with sex-selected, frozen-thawed (FT) spermatozoa has been limited by the significant expense of the sorting process. Reducing the total number of progressively motile sperm (PMS) required for an AI would reduce the sorting cost. As such, this research compared the efficacy of small-dose deep uterine AI with sexed FT spermatozoa (SEXED-SMALL; ~50×10(6)PMS, n=20), to a moderate dose deposited mid-horn (SEXED-STD, ~200×10(6)PMS; n=20), and a large dose of FT non-sexed spermatozoa deposited in the uterine body (NONSEXED-LARGE, 660×10(6)PMS, n=9). Ten of the 11 calves resulting from use of sexed spermatozoa were of the predetermined sex. Similar rates of conception (NONSEXED-LARGE: 78%, SEXED-STD: 60%, SEXED-SMALL: 57%) and total pregnancy loss (TPL: NONSEXED-LARGE: 28.6%; SEXED-STD: 41.0%; SEXED-SMALL: 63.6%) were observed across groups, but early pregnancy loss (EPL, <day 120 post-conception) was greater (P=0.04) for SEXED-SMALL (54.5%) compared to NONSEXED-LARGE (0%). Animals experiencing EPL were older (31.3 y, P=0.007) than those that calved (21.4y) or did not conceive (19.4y). After excluding females ≥25y, SEXED-SMALL (15.4%) had a tendency for having reduced calving rates compared to NONSEXED-LARGE (50.0%; P=0.08), while SEXED-STD did not differ (40.0%, 4/10; P=0.341). Current findings indicate that acceptable conception and calving rates using sexed FT spermatozoa are achieved after mid-horn deposition of 200×10(6) PMS, when used with females aged less than 25 y.

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.

Traversing the ovine cervix - a challenge for cryopreserved semen and creative science

This review brings together research findings on cervical relaxation in the ewe and its pharmacological stimulation for enhancement of the penetration needed for transcervical insemination and embryo transfer. On the basis that the success of artificial insemination is the percentage of ewes lambing, a review is made of recent research aimed at understanding and minimising the sub-lethal effects of freezing and thawing on the viability of spermatozoa, their membrane integrity and their ability to migrate through cervical mucus, as these characteristics have a major influence on fertility, particularly when semen is deposited, artificially, in the os cervix. Milestones of achievement are given for transcervical intrauterine insemination, embryo recovery and transfer and the birth of lambs of pre-determined sex, firstly following intracytoplasmic sperm injection, then laparoscopic intrauterine insemination using highly diluted flow-cytometrically sorted fresh semen and subsequently by os cervix insemination using sexed semen that had been frozen and thawed. Diversity of research endeavour (applied, cellular, molecular), research discipline (anatomy, histology, immunology, endocrinology) and research focus (cell, tissue, organ, whole animal) is embraced within the review as each has significant contributions to make in advancing recent scientific findings from the laboratory into robust on-farm transcervical insemination and embryo transfer techniques.

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.

Two-dimensional polyacrylamide gel electrophoresis of membrane proteins from flow cytometrically sorted ram sperm

Membrane proteins orchestrate key events required for participation of sperm in fertilisation. These proteins may be removed or altered due to the mechanical and dilution stressors associated with sex-sorting of sperm. Ram sperm were incubated with Hoechst 33342 and flow-sorted. Sex-selected (viable, orientated) and waste (separated into non-viable or non-orientated) sperm populations were collected, or sperm were not sorted. Sperm membrane proteins were extracted and characterised by one- and two-dimensional PAGE. Densiometric analysis of protein bands separated by one-dimensional PAGE showed proteins of 30 and 28 kDa as doublet bands on non-sorted sperm, and single bands on sex-sorted sperm, and the proportion of a 14 kDa protein was 3-fold higher in non-sorted compared to sorted sperm. Proteins in the 14 kDa band were identified by mass spectroscopy as a bovine Fibronectin type-2 protein (Fn-2), cytochrome oxidase 5a (Cox5a) and a sperm membrane associated protein (SLLP1). The abundance of these proteins in the two-dimensional gels was lowest in the sorted sperm population identified as viable during sorting (orientated and non-orientated sperm) and highest in the non-viable sperm population (P < 0.001). We concluded that the membrane protein profile was different for sex-sorted compared with non-sorted sperm, due to the selection of plasma membrane-intact cells in the flow-sorted population. This provided further evidence that sex-sorting selected a homogenous population of sperm with superior function to non-sorted sperm. Furthermore, this was apparently the first time sperm membrane acrosome associated protein was reported in ram sperm, and it was demonstrated that seminal plasma proteins remained on the sperm membrane after sex-sorting.

Improving the efficiency of insemination with sex-sorted spermatozoa

The sorting of X- and Y-chromosome-bearing spermatozoa by flow cytometry is nowadays one of the most apt assisted-reproduction technologies in livestock production. Potential economic and biological benefits, as well as those related to easier management of herds, have been reported arising out of the application of this technique, especially in cattle. Yet, the sex-sorting procedure induces damage to spermatozoa, affecting their function and fertilizing ability. Different species present varying degrees of susceptibility to damage from the sorting process and each has its own requirements for sex-sorted insemination procedures. Thus, several new protocols and strategies have been designed for the handling of sorted spermatozoa, with the main objective of optimizing their fertilizing ability and the consequent application of flow-cytometric sex-sorting technology. This article reviews current advances in this technology, pointing out the components to be improved before this technology may be widely applied in different domestic species.