New Artificial Insemination Technologies for Swine

Artificial insemination and optimization of the use of seminal doses in swine

The optimization of processes associated with artificial insemination (AI) is of great importance for the success of the pig industry. Over the last two decades, great reproductive performance has been achieved, making further significant progress limited. Optimizing the AI program, however, is essential to the pig industry's sustainability. Thus, the aim is not only to reduce the number of sperm cells used per estrous sow but also to improve some practical management in sow farms and boar studs to transform the high reproductive performance to a more efficient program. As productivity is mainly influenced by the number of inseminated sows, guaranteeing a constant breeding group and with healthy animals is paramount. In the AI studs, all management must ensure conditions to the health of the boars. Some strategies have been proposed and discussed to achieve these targets. A constant flow of high-quality and well-managed breeding groups, quality control of semen doses produced, more reliable technology in the laboratory routine, removal of less fertile boars, the use of intrauterine AI, the use of a single AI with control of estrus and ovulation (fixed-time AI), estrus detection based on artificial intelligence technologies, and optimization regarding the use of semen doses from high genetic-indexed boars are some strategies in which improvement is sought. In addition to these new approaches, we must revisit the processes used in boar studs, semen delivery network, and sow farm management for a more efficient AI program. This review discusses the challenges and opportunities in adopting some technologies to achieve satisfactory reproductive performance and efficiency.

Supplementing Boar Diet with Nicotinamide Mononucleotide Improves Sperm Quality Probably through the Activation of the SIRT3 Signaling Pathway

Sperm quality is an important indicator to evaluate the reproduction ability of animals. Nicotinamide mononucleotide (NMN) participates in cell energy metabolism and reduces cell oxidative stress. However, the effect and regulatory mechanism of NMN on porcine sperm quality are still unknown. Here, 32 Landrace boars were randomly assigned to four groups (n = 8) and fed with different levels of NMN (0, 8, 16 or 32 mg/kg/d) for 9 weeks, and then serum and semen samples of the boars were collected to investigate the function and molecular mechanism of NMN in sperm quality. The results showed that the dietary NMN supplementation significantly increased sperm volume, density and motility (p < 0.05). Interestingly, NMN apparently improved the antioxidative indexes and increased the levels of testosterone (p < 0.05) in serum. Furthermore, NMN upregulated the protein levels of sirtuin 3 (SIRT3), antioxidation and oxidative phosphorylation (OXPHOS), but downregulated the protein levels of apoptosis in semen. Mechanically, NMN protected sperm from H2O2-induced oxidative stress and apoptosis through SIRT3 deacetylation. Importantly, the SIRT3-specific inhibitor 3-TYP attenuated the antioxidation and antiapoptosis of NMN in sperm. Therefore, NMN exerts antioxidation and antiapoptosis to improve boar sperm quality via the SIRT3 signaling pathway. Our findings suggest that NMN is a novel potential boar antioxidative feed additive to produce high-quality porcine semen.

Impact of inclusion of post-spermatic ejaculate fraction in boar seminal doses on sperm metabolism, quality, and interaction with uterine fluid

Boar ejaculate is composed of sperm cells and seminal plasma (SP) and is emitted in different fractions (pre-sperm fraction; spermatic-rich fraction; intermediate fraction; post-spermatic fraction), with different composition of SP and volume, which could influence the sperm quality during seminal doses preparation, conservation, and interaction with the female reproductive tract. In artificial insemination (AI) centers, seminal doses are usually prepared with the spermatic-rich and intermediate fractions, but the inclusion of other ejaculate fractions, although controversial, is beginning to be applied. The objective was to evaluate the synergic effect of accumulative ejaculated fractions on sperm functionality during seminal doses preparation, throughout storage and after incubation with uterine fluid (UF). For this purpose, a total of 57 ejaculates were collected, and the following experimental groups were prepared (n = 19 per group): (F1) spermatic-rich fraction; (F2) F1 plus intermediate fraction; (F3) F2 plus post-spermatic fraction. Each group was stored for 5 days at ∼16 °C, and the following parameters were evaluated: sperm metabolism of pure and diluted semen (day 1), sperm quality parameters (days 1, 3, 5), thermal-resistance test (TRT) and incubation with uterine fluid (UF) (day 5). Sperm metabolic rates between accumulative ejaculate fractions from pure and diluted semen did not show differences. Also, sperm quality parameters were not affected by the ejaculate fraction during storage. However, sperm subjected to TRT showed similar results except for progressive motility, which was better in F2 and F3 than F1. When sperm were incubated with UF, the quality decreased in each group, but sperm from F2 and F3 were less affected than those from F1. In conclusion, the post-spermatic fraction can be included in seminal doses for their use in AI-centers, with functionality of sperm of different SP origins not being impaired throughout the storage, and responding better to thermal and UF stress. However, further research in AI-centers is necessary to test the sperm behaviour under presented conditions.

Sperm concentration of boar semen doses and sperm quality: Novel perspectives based on the extender type and sperm resilience

This study evaluated the effect of sperm concentration of boar semen doses on their capacity to maintain its motility over the thermo-resistance test (TRT; sperm resilience) and verified if the extender type (short or long-term) could influence this effect. Thirty ejaculates from five crossbred mature PIC® boars were used, and a factorial design was followed to produce semen doses with 1.5 billion cells in 45 or 90 mL, using Beltsville Thawing Solution (BTS) or Androstar® Plus (APlus). Then, low-concentration doses (16.7 × 10⁶ cells/mL in 90 mL) and higher-concentration doses (33.3 × 10⁶ cells/mL in 45 mL) with BTS or APlus were produced and stored at 17 °C for 168 h. At 72 h, during the TRT, the low-concentration doses (16.7 × 10⁶ cells/mL) lost three-fold less motility than doses with 33.3 × 10⁶ cells/mL (P < 0.01), regardless of the extender type (11. 5% vs. 30.5% of initial motility, respectively). Similar results were found when the TRT was carried out at 168 h, with low-concentration doses losing two-fold less motility (11.4%) than highly concentrated doses (25.9%; P < 0.01). No sperm concentration effect was observed on membrane integrity or mitochondrial membrane potential (P ≥ 0.23). The osmolarity was not affected by the sperm concentration (P = 0.56), only by the extender and the storage time (P < 0.01). In conclusion, the sperm concentration effect on sperm quality was not influenced by extender type, and the data suggest that a low concentration of semen doses positively affects sperm resilience.

Science-based quality control in boar semen production

The ever-increasing understanding of sperm physiology, combined with innovative technical advances, continuously furthers the development of boar semen production management. These improvements pave the way for the future implementation of modified quality assurance concepts. This review provides an overview of current trends and new approaches in boar semen production, focusing on: the improvement of hygienic standards, alternatives to the use of antibiotics including the application of cold temperature storage and the utilization of antimicrobial additives, as well as the implementation of new quality control tools. Furthermore, the influence of dilution and temperature management, as well as new possibilities for an improvement of boar semen shipping and storage conditions are reviewed.

Update on artificial insemination: Semen, techniques, and sow fertility

Over the years, reproductive efficiency in the swine industry has focused on reducing the sperm cell number required per sow. Recent advances have included the identification of subfertile boars, new studies in extended semen quality control, new catheters and cannulas for intrauterine artificial insemination (AI), and fixed-time AI under commercial use. Therefore, it is essential to link field demands with scientific studies. In this review, we intend to discuss the current status of porcine AI, pointing out challenges and opportunities to improve reproductive efficiency.

Intensity and Duration of Vibration Emissions during Shipping as Interacting Factors on the Quality of Boar Semen Extended in Beltsville Thawing Solution

Vibration emissions during the transport of boar semen for artificial insemination (AI) affect sperm quality. In the present study, the common influence of the following factors was investigated: vibrations (displacement index (D_i) = 0.5 to 6.0), duration of transport (0 to 12 h) and storage time (days 1 to 4). Normospermic ejaculates were collected from 39 fertile Pietrain boars (aged 18.6 ± 4.5 months) and diluted in a one-step procedure with an isothermic (32 °C) BTS (Minitüb) extender (n = 546 samples). Sperm concentration was adjusted to 22 × 10⁶ sperm·mL^-1. Extended semen (85 ± 1 mL) was filled into 95 mL QuickTip Flexitubes (Minitüb). For transport simulation on day 0, a laboratory shaker IKA MTS 4 was used. Total sperm motility (TSM) was evaluated on days 1 to 4. Thermo-resistance test (TRT), mitochondrial activity (MITO) and plasma membrane integrity (PMI) were assessed on day 4. Sperm quality dropped with increasing vibration intensity and transport duration, and the effect was enhanced by a longer storage time. A linear regression was performed using a mixed model, accounting for the boar as a random effect. The interaction between D_i and transport duration significantly (p < 0.001) explained data for TSM (-0.30 ± 0.03%), TRT (-0.39 ± 0.06%), MITO (-0.45 ± 0.06%) and PMI (-0.43 ± 0.05%). Additionally, TSM decreased by 0.66 ± 0.08% with each day of storage (p < 0.001). It can be concluded that boar semen extended in BTS should be transported carefully. If this is not possible or the semen doses are transported a long way, the storage time should be reduced to a minimum.

Past, present and future of ICSI in livestock species

During the past 2 decades, intracytoplasmic sperm injection (ICSI) has become a routine technique for clinical applications in humans. The widespread use among domestic species, however, has been limited to horses. In horses, ICSI is used to reproduce elite individuals and, as well as in humans, to mitigate or even circumvent reproductive barriers. Failures in superovulation and conventional in vitro fertilization (IVF) have been the main reason for the use of this technology in horses. In pigs, ICSI has been successfully used to produce transgenic animals. A series of factors have resulted in implementation of ICSI in pigs: need to use zygotes for numerous technologies, complexity of collecting zygotes surgically, and problems of polyspermy when there is utilization of IVF procedures. Nevertheless, there have been very few additional reports confirming positive results with the use of ICSI in pigs. The ICSI procedure could be important for use in cattle of high genetic value by maximizing semen utilization, as well as for utilization of spermatozoa from prepubertal bulls, by providing the opportunity to shorten the generation interval. When attempting to utilize ICSI in ruminants, there are some biological limitations that need to be overcome if this procedure is going to be efficacious for making genetic improvements in livestock in the future. In this review article, there is an overview and projection of the methodologies and applications that are envisioned for ICSI utilization in these species in the future.

Does a single fixed-time insemination in weaned sows affect gestation and lactation length, and piglet performance during lactation compared with multiple insemination protocols in a commercial production setting?

This study evaluated the effect of different single fixed-time artificial insemination (FTAI) protocols on gestation length, farrowing distribution (synchrony), and piglet performance. In Study 1, 866 sows were assigned to two groups: Multiple AI (n = 484) - multiple artificial insemination (AI) at 24 h intervals during estrus; and FTAI+MultAI (n = 382) - OvuGel® 96 h post-weaning and single FTAI 22-24 h later. In Study 2, FTAI protocols were retrospectively analyzed: pLH - sows received 2.5 mg (Exp.1, n = 184) or 5 mg (Exp.2, n = 362) of porcine luteinizing hormone (pLH) at estrus onset, and single FTAI 24 h later. The FTAI+MultAI resulted in shorter gestation length (P < 0.01) and greater synchrony of farrowing on days 114-115 of gestation (P < 0.01) than Multiple AI. Longer lactation length (21.2 vs. 20.9 d; P = 0.02) and greater piglet weaning weight (5378.9 ± 73.1 vs. 5153.2 ± 74.4 g; P = 0.03) for FTAI+MultAI compared to Multiple AI were observed. In Study 2, the gestation length based on the first AI record was shorter for FTAI and resulted in greater synchrony of farrowing on days 114-115 of gestation, compared with Multiple AI (P ≤ 0.05). Gestation length did not differ between groups (P > 0.05) when measured based on most probable AI responsible for fertilization (ultrasound evaluation). In conclusion, FTAI resulted in shorter gestation length and greater farrowing synchrony compared with Multiple AI. Longer lactation length and greater piglet weaning weight were observed for FTAI compared with multiple insemination protocols.

Single Fixed-Time Post-Cervical Insemination in Gilts with Buserelin

Current protocols for gilts recommend the deposit of multiple semen doses in the cervix each 12-24 h after estrus detection. Our objectives were: (1) to determine the effect of buserelin and a single fixed-time artificial insemination using the new post-cervical artificial insemination technique (FTAI-PCAI) on reproductive and productive performance in gilts, and (2) to compare this protocol with conventional estrus detection and double PCAI without hormonal induction. In the control group (C; n = 240), gilts were inseminated twice (8 and 12 h from estrus onset). Gilts in the treatment group (T; n = 226) received buserelin (10 μg, intramuscular) 120 h after altrenogest treatment (18 d) and one single PCAI 30-33 h after buserelin administration. The groups did not differ in reproductive and production performance (p > 0.05). The T group showed greater piglet birth weight and shorter estrus duration (p < 0.001). Delivery batch length differed significantly depending on the season (p < 0.05); the shortest length corresponded to autumn. Both groups only differed significantly in spring (p = 0.018), with a shorter length in the T group. This new FTAI-PCAI protocol with buserelin is recommended in gilts, helping with optimization of genetic diffusion, boars, and semen doses.

Seasonal Changes of Nuclear DNA Fragmentation in Boar Spermatozoa in Spain

Simple Summary

Artificial insemination is widely used in pig production and currently a boar performs several thousand matings per year. Traditionally sperm quality is focused on the number of spermatozoa, their motility and morphology. However, the quality of sperm DNA, which contains genetic information, is also related to fertility problems. The aim of this research was to study the effect of natural light hours and age of the boar on the status of the sperm DNA. After a powerful statistical analysis, it was found that the percentage of spermatozoa with fragmented DNA decreases within the observed age range as the boar gets older. On the other hand, the amount of spermatozoa with fragmented DNA was the lowest in autumn while it was the highest in summer. This study demonstrates the remaining seasonality of boars in Spain and highlights the importance of controlling the environmental conditions in the farms. Sperm DNA testing provides a basis for improving the selection of AI boars by excluding males with higher DNA fragmentation due to their very young reproductive age that may pose a potential subfertility.

Abstract

There are numerous cases when conventional spermiogram parameters are all within an acceptable range but boar subfertility persists. The total sperm nuclear DNA fragmentation index (tDFI) is a trait related to fertility and prolificacy problems that is not routinely evaluated in commercial AI boars. The aim of this research was to study the effect of the photoperiod, season and reproductive age of the boar on tDFI (measured by SCSA) of 1279 ejaculates from 372 different boars belonging to 6 different breeds located in 6 AI studs in Spain. tDFI data ranged from 0.018% to 20.1%. Although there was a significant single boar effect in the tDFI occurrence, a negative correlation between the tDFI and the age of the boar was found (p < 0.001). tDFI would decrease due to aging of the boar 0.66% each year old within the observed age range. After including age as a covariate in the ANCOVA, no differences were found in tDFI between photoperiods when the sperm collection date was evaluated. However, when the date of the production of semen in the testis was evaluated, the total percentage of spermatozoa with fragmented nuclear DNA was 1.46% higher in the increasing photoperiod in comparison to the decreasing photoperiod (p < 0.0001). On the other hand, for both dates, the lowest tDFI values corresponded to minimum day length for decreasing photoperiod phase (autumn), while the highest tDFI values were found in summer (maximum day length for decreasing photoperiod phase).

Extracellular Vesicles, the Road toward the Improvement of ART Outcomes

Nowadays, farm animal industries use assisted reproductive technologies (ART) as a tool to manage herds' reproductive outcomes, for a fast dissemination of genetic improvement as well as to bypass subfertility issues. ART comprise at least one of the following procedures: collection and handling of oocytes, sperm, and embryos in in vitro conditions. Therefore, in these conditions, the interaction with the oviductal environment of gametes and early embryos during fertilization and the first stages of embryo development is lost. As a result, embryos obtained in in vitro fertilization (IVF) have less quality in comparison with those obtained in vivo, and have lower chances to implant and develop into viable offspring. In addition, media currently used for IVF are very similar to those empirically developed more than five decades ago. Recently, the importance of extracellular vesicles (EVs) in the fertility process has flourished. EVs are recognized as effective intercellular vehicles for communication as they deliver their cargo of proteins, lipids, and genetic material. Thus, during their transit through the female reproductive tract both gametes, oocyte and spermatozoa (that previously encountered EVs produced by male reproductive tract) interact with EVs produced by the female reproductive tract, passing them important information that contributes to a successful fertilization and embryo development. This fact highlights that the reproductive tract EVs cargo has an important role in reproductive events, which is missing in current ART media. This review aims to recapitulate recent advances in EVs functions on the fertilization process, highlighting the latest proposals with an applied approach to enhance ART outcome through EV utilization as an additive to the media of current ART procedures.

Weaned Sows with Small Ovarian Follicles Respond Poorly to the GnRH Agonist Buserelin

Simple Summary

This study evaluated the influence of mean ovarian follicle size and the season of weaning on the effectiveness of administering the GnRH agonist buserelin to synchronize ovulation in weaned sows. The results from 352 sows demonstrated that sows with small follicles (<0.5 cm in diameter) at treatment are poor responders, a condition more frequent among sows weaned in summer–autumn than in those weaned in winter–spring.

Abstract

The GnRH agonist buserelin (GnRH), used to synchronize ovulation in weaned sows, attains only 70–80% effectivity, owing to several reasons of ovarian origin. This study evaluated in particular whether mean ovarian follicle size at treatment and the season of weaning are among those influencing GnRH responsiveness. The experiment was carried out in a temperate-region farm with 352 sows of 1–6 parities weaned either in winter–spring (WS, 174 sows) or in summer–autumn (SA, 178 sows). The sows were randomized into two groups: GnRH (10 µg of buserelin acetate at 86 h after weaning, 172 sows) and control (180 sows). The ovaries were transrectally scanned from weaning to ovulation and the sows clustered according to their mean follicular size at treatment time: small (<0.5 cm in diameter), medium (0.5 to 0.64 cm) and large (0.65 to 1.09 cm). In total, 88.33% of the GnRH-treated sows ovulated, with 82% of them within the expected time window (120–132 h after weaning). In contrast, 95.45% of the unresponsive sows had small follicles at the time of treatment and were mostly weaned in SA (20.45%) than in WS (4.76%). In conclusion, the conspicuous presence of sows having small ovarian follicles at treatment time compromises the efficiency of the GnRH agonist buserelin to synchronize ovulation in weaned sows, which occurs more frequently in summer–autumn weaning.

Reproductive performance in cervical and postcervical artificial insemination (PCAI) with liquid boar semen in Gunghroo × Hampshire crossbreed pig in Nagaland

Genetic advancement for the modern swine industry is primarily accomplished through the use of reproductive biotechnology, mainly artificial insemination (AI). The objective of the present study was to compare the fertility outcome by cervical and post-cervical artificial insemination (PCAI) using normal (three billion) and reduced (one billion) number of spermatozoa in pig. Pluriparous weaned sows were grouped into 4 groups, i.e. Group- 1, AI with three billion spermatozoa by intra-cervical insemination; Group-2, AI with one and half billion spermatozoa by intra-cervical insemination; Group-3, AI with three billion spermatozoa by PCAI and Group-4, AI with one and half billion spermatozoa by PCAI. Non-significantly higher farrowing rate was recorded in Group-3 compared to Group-1. Post-cervical AI with lower number of spermatozoa (Group-4) resulted into farrowing rate which was similar to cervical insemination with higher number of spermatozoa (Group-1). There was significant difference in litter size at birth and litter size at weaning between Group-1 and 2. Litter size at birth and litter size at weaning was significantly higher in Group-4 compared to Group-2. Also, litter size at birth and litter size at weaning was significantly higher in PCAI animals (Group-2 and 4) compared to cervical inseminated animals (Group-1 and 2). In conclusion, PCAI with liquid boar semen was found to have improved farrowing rate, litter size at birth and litter size at weaning compared to cervical insemination.

Relationship between pubertal testicular ultrasonographic evaluation and future reproductive performance potential in Piétrain boars

New ways of predicting sperm quality and output performance in young artificial insemination (AI) boars are important for breeding companies to ensure that the pubertal boars delivered to the AI studs have a high chance of meeting minimum quality standards to be used for insemination and therewith dissemination of desirable characteristics. The aim of the current study was to characterize the testicular development of 218 pubertal Piétrain boars (Line 408, Pig Improvement Company) to identify traits with predictable characteristics relative to their sperm quality as an adult AI boar. Scrotum, testes and epididymis were examined ultrasonographically at day (d) 100 (on-test) and 170 (off-test) followed by a computer-assisted grayscale analysis (GSA). Over the test period, paired testicular volume increased 7.3-fold from 22.7 ± 10.8 cm³ to 166.6 ± 62.2 cm³. The right testis was significantly (P = 0.014) larger than the left one at the off-test. Based on the sperm quality (ejaculate volume, sperm concentration, total sperm number, morphologically abnormal sperm and total sperm motility at day 3 of semen storage), 82.11% (n = 179) of the boars were classified as "productive" boars. These boars had a significantly (P = 0.039) larger paired testicular volume than "non-productive" boars (45.9 ± 19.9 cm³vs. 38.5 ± 12.6 cm³) at the on-test. For the right testis at on-test, significant differences for the standard deviation of mean gray value (P = 0.022), area under the curve (P = 0.004) and mean gradient value (GRAD, P = 0.030) regarding the future sperm production capacity (SPC) were shown. At off-test, there was a significant difference for minimum gray value (MIN GV, P = 0.003) and mean gray value (P = 0.001) related to SPC. To find SPC related cut-off values for GSA data, a two segmental non-linear regression analysis was carried out indicating breakpoints for GRAD ≥12 and MIN GV ≥ 40 for boars with low SPC. Off-test boars with MIN GV ≥ 40 showed a 2.4 higher risk to display low SPC (Odds ratio = 2.4 [1.1, 5.4]; P = 0.024). The results may enable breeding companies to include new sperm quality associated traits in their boar testing and selection programs.

Insemination of sows with seminal doses prepared by a two-step hypothermic dilution does not impair the reproductive performance at farm

Reproduction in swine is mostly carried out through artificial insemination (AI). For this purpose, AI studs collect the ejaculates, analyse the sperm quality, dilute and package to produce seminal doses and ship them to sow farms to carry out the AI. Temperature is controlled during the process to avoid sperm damage. Semen is diluted in the extender in a one-step or a two-step process where the second can be isothermic (approximately 32°C) or hypothermic (room temperature 21-22°C). Both techniques are currently performed, and the latter could reduce time and costs, but the literature available comparing the processes is scarce and presents discrepancies. To date, there are no studies about its impact in fertility. This study compared hypothermic two-step dilution (HTSD) and isothermic two-step dilution (ITSD) in laboratory and field trial to elucidate whether HTSD has any effect. Ejaculates from 72 boars in nine AI studs were split and processed with both techniques using a high-performance extender and evaluated in laboratory. Four farms inseminated 345 sows with samples of four of these AI studs, and their fertility and prolificacy were registered. Results show no significant differences between doses prepared by HTSD and ITSD technique, having no impact in laboratory results (percentage of motile sperm, short hypoosmotic swelling test (sHOST) and short osmotic resistance test (sORT), viable sperm, damaged acrosomes, sperm under early apoptosis, high mitochondrial membrane potential (p > .1), fertility (92.2% versus 94.1%, p = .45) or farrowing rate (15.8 ± 0.3 versus 16.1 ± 0.3 p = .46). In conclusion, our results suggest that HTSD of semen on extender could be safely implemented in AI studs under the conditions tested.

Rest days and storage of boar semen at 17°C: Effect on motility and sperm concentration

Boar fertility is an important factor in farm production; it is therefore of interest to determine factors which reduce the fertilising capacity of semen samples stored at 17°C for use in intrauterine insemination. This work evaluated the effect of the number of rest days between each mounting of the boar, and the number of days that the semen was stored at 17°C, on sperm motility and semen concentration. We also analysed whether the boar's age influenced the sperm concentration. The results showed that only the total motility diminished as the storage time at 17°C increased (p < .05). A low negative correlation was observed between the variables' rest days and total and progressive motility. The sperm concentration presented no relation with rest days or the boar's age. The boars' rest days had no effect on motility and sperm concentration in the males studied, allowing them to be used with the frequencies described with no effect on these parameters.

Antibiotic-free extended boar semen preserved under low temperature maintains acceptable in-vitro sperm quality and reduces bacterial load

This study aimed to assess the sperm quality and number of colony-forming units (CFU mL^-1) in extended boar semen stored at low temperatures with or without antibiotics. Normospermic ejaculates (n = 34) were diluted in split samples with Androstar® Premium with or without antibiotics (ampicillin and apramycin sulfate). The extended semen doses were stored for 120 h under three storage temperatures (5, 10, and 17 °C). Variables were analyzed as repeated measures using the GLIMMIX procedure, in a factorial design. The extended semen doses under low-temperature storage (5 and 10 °C) had total motility above 75% throughout the storage. The interaction antibiotic × temperature was significant for total (P = 0.004) and progressive motility (P = 0.005). In extended boar semen doses with antibiotics, the total and progressive motility increased as the storage temperature increased (80.2%, 84.5%, and 89.1%; 70.5%, 76.0%, and 82.9% for total and progressive motility at 5, 10, and 17 °C, respectively; P < 0.05). In extended semen doses without antibiotics, the total and progressive motility were lower when stored at 5 °C than at 10 °C and 17 °C (81.8%, 85.4% and 86.6% and 71.9%, 76.7%, 78.9% for total and progressive motility at 5, 10, and 17 °C, respectively; P < 0.05). After the thermoresistance test, total and progressive motility of doses with antibiotics were higher at 17 °C than 5 °C (P < 0.05); however, they were not affected (P > 0.05) by storage temperature in extended semen doses without antibiotics. The number of CFU mL^-1 was lower in extended semen doses without antibiotics stored at 5 and 10 °C than at 17 °C (P < 0.05); however, in extended semen doses with antibiotics, no effect of storage temperature was observed (P > 0.05). The bacterial load was greater in extended semen without antibiotics than with antibiotics, regardless of the storage temperature (P < 0.05). The acrosome and sperm membrane integrity were not influenced (P > 0.05) by using antibiotics. A higher percentage of normal acrosomes was observed as the storage temperature increased (93.6%, 94.3%, and 96.8% at 5, 10, and 17 °C, respectively; P < 0.0001). The membrane integrity was higher (P < 0.0001) in extended semen doses stored at 17 °C than at 10 or 5 °C. The pH rose throughout the storage in all the treatments, except in extended semen doses stored at 17 °C without antibiotics, in which a decrease in the pH occurred at 120 h (P < 0.05). Although the sperm quality being negatively affected by low temperatures, the storage of extended boar semen doses at 5 °C is possible since the sperm viability in vitro was maintained for up to 5 days, fulfilling the requirements of semen quality to be used in artificial insemination. Nevertheless, the use of extended semen doses without antibiotics requires the optimization of hygiene procedures during semen dose processing.

Antibiotics and their alternatives in Artificial Breeding in livestock

Antibiotics are mandatory components of semen extenders for the control of bacterial contamination and growth. The increasing rate of worldwide resistance to conventional antibiotics in semen preservation media requires the development of new antimicrobial alternatives. This review provides an update on this topic and also highlights the improvement of hygiene in Artificial Insemination centers in order to prevent the development of bacterial resistance. Ideas are shared on future diagnostic tools for bacterial contamination in Artificial Breeding. Finally, new methods to remove or reduce bacteria in semen will be discussed.

Effect of boar seminal dose type (cervical compared with post-cervical insemination) on cooling curve, sperm quality and storage time

Seminal doses used for cervical and post-cervical artificial insemination (CAI and PCAI, respectively) vary in volume, the number of spermatozoa and packaging. The aim was to evaluate the outcomes when there was use of routine processing procedures for CAI- and PCAI-doses. Two different types of seminal doses were processed: 1) CAI: 2.7 × 10⁹ sperm/80 ml; 2) PCAI: 1.5 × 10⁹ sperm/45 ml. In Experiment 1, the cooling curve of seminal doses during processing occurred in two phases: 1st) At room temperature (23.4 ± 0.5 °C) from 0 (just after packaging) to 120 min; 2nd) At refrigeration (15.7 ± 0.8 °C) from 121-240 min. For the PCAI-doses, the time required to reach room temperature was 47 min compared to 107 min for CAI-doses (decreasing velocity of 0.093 °C/min and 0.048 °C/min, respectively). During refrigeration, for the PCAI-doses the time required to reach the desired preservation temperature was 20 min less than for CAI-doses (PCAI: 90 min, 0.074 °C/min; CAI: 110 min, 0.066 °C/min). In Experiment 2, sperm motility, kinetic parameters and acrosome damage for both types of doses were evaluated at 0, 24, 48 and 72 h of refrigeration. Also, morphology, pH, and osmolality were assessed at 0 and 72 h. Values for all these did not differ between CAI- and PCAI-doses. In conclusion, PCAI-doses took less time than CAI-doses to reach the desired temperature, but sperm quality was similar for CAI- and PCAI-doses during storage. Nevertheless, the different cooling curves should be taken into consideration for further investigation.

Post-cervical compared with cervical insemination in gilts: Reproductive variable assessments

The aim with this study was to compare cervical (CAI; 3 × 10⁹ spermatozoa/90 mL) and post-cervical (PCAI; 1.5 × 10⁹ spermatozoa/45 mL) artificial insemination (AI) techniques for frequency of incidences (unsuccessful or difficult probe passage, backflow, metritis and bleeding), values for reproductive variables and duration of the procedure in gilts. There were 644 gilts (255-270 days old, weighing 150 ± 5 kg) randomly assigned to PCAI (n = 320) and CAI (n = 324) groups. In total, there were 957 and 958 artificial inseminations performed in the CAI and PCAI groups, respectively (2-4 AIs/gilt). The frequency of unsuccessful or difficult PCAI probe passage/AI was 14.6% (140/958), therefore, there was a 85.7% probe passage success/AI rate (818/958). The semen backflow frequency/AI was less with PCAI than CAI (4.3% compared with 8.2%, P <  0.001). With the PCAI group, there were only a few cases of bleeding (11/958: 1.1% /AI) with no difference between the CAI and PCAI groups (P = 0.224). In gilts (n = 72) where there was not passage of the PCAI probe (72/320; 22.5%) there was use of CAI, (M, mixed group). For the CAI, PCAI and M groups, there were similar values for positive pregnancy diagnosis, farrowing rates and prolificacy (P > 0.05). The average duration for AI was shorter in the PCAI (2.34 ± 0.809 min) than CAI (4.77 ± 1.059 min) group, and it was longer in the M group (7.48 ± 2.454 min; P < 0.050). The PCAI procedure, therefore, is recommended for AI of gilts.

Combining Fixed-Time Insemination and Improved Catheter Design in an Effort to Improve Swine Reproduction Efficiency

Conventional practice is to breed sows by artificial insemination (AI) at least twice using approximately three billion sperm per insemination upon estrus at standing heat. This research explored the use of combined technologies, including fixed-time insemination (FTAI) and an alternative catheter design that reportedly reduces semen backflow, in order to reduce the number of inseminations and the semen dosage and maintain reproductive efficiency. The FTAI technique used in this study was to inject I.M. 600 IU equine chorionic gonadotropin (eCG) at weaning and 5 mg porcine luteinizing hormone (pLH) to stimulate ovulation 80 h later, followed by a single insemination 36 h after the pLH injection. The two catheters used in this study were a conventional foam-tipped insemination catheter and a Gedis catheter. The Gedis catheter is designed to be completely inserted into the vagina. The semen is enclosed along the length of the rod and held in place by a gel cap that melts when inserted into the cervix. Sows were assigned to the following treatments: Group 1 (n = 135), bred twice with a conventional catheter and a standard semen dose of approximately three billion sperm in 80 mL; Group 2 (n = 123), FTAI with conventional catheter and a standard semen dose; Group 3 (n = 127), FTAI with Gedis catheter and a standard semen dose; Group 4 (n = 126), FTAI with Gedis catheter and a reduced semen dose with one billion sperm. The farrowing rates were 81.6%, 77.7%, 74.0%, and 62.7% for Groups 1 to 4, respectively. The likelihood of farrowing was lower for Group 3 and Group 4 compared to Group 1 (odds ratio (OR) = 0.57; p = 0.08 and OR = 0.35; p = 0.001, respectively). Likewise, litter size of Group 3 and Group 4 was smaller than Group 1 (p = 0.006 and p = 0.04, respectively). Overall, the combination of Gedis catheter and FTAI resulted in decreased reproductive performance that outweighed the value of using less semen.

Application of preserved boar semen for artificial insemination: Past, present and future challenges

Artificial insemination (AI) is now used for breeding more than 90% of the sows in most of the world's primary pork producing countries. Despite the advancement of methods to cryopreserve boar semen, frozen semen has not been routinely used on farms because of limited efficiency. Liquid semen on the other hand, with 1.5-3 billion sperm per dose preserved up to seven days in long-term extenders, is in common use and is largely responsible for the widespread use of AI. Breeding organizations have defined individual thresholds for useable semen at 60-80% for motility and bacterial load of 0-1000 CFU/mL. Improvement in preservation techniques for liquid semen and better education of producers has been responsible for the higher efficiency of pig breeding, as measured by conception rate and increased litter size, with a minimum number of sperm. The introduction of deep intrauterine AI and advances in breeding management have also been contributing factors. The present article reviews the worldwide application of preserved boar semen from past to present and delineates future challenges. Pathways to increase breeding efficiency are outlined. The reconciliation of AI with sustainable breeding strategies is increasingly important. In this sense, guidelines for the prudent use of antibiotics in semen extenders are proposed. More efficient and sustainable pig AI awaits the introduction of sex-sorted sperm into AI practice. Another critical milestone that needs to be achieved is the replacement of conventional antibiotics in extenders.

New trends in production management in European pig AI centers

Reducing the number of spermatozoa per artificial insemination (AI) dose and managing semen in ways to ensure greater quality at the same time represents current challenges with sperm processing in pig AI centers. Based on a multi-year comparative analysis of process steps in different pig AI centers, and complementary experimental studies under standardized laboratory conditions, current process standards for the preservation of boar semen have been updated and new ones developed. Currently, these standards represent an integral part of the quality assurance of 29 European pig AI centers in ten different organizations in Germany, Switzerland and Austria. Improvement of hygiene management and guidelines for prudent use of antibiotics have become key issues. Furthermore, new quality control tools have been implemented in the processing and transport of boar semen: e.g. refractometry as an easy-to-use tool to estimate extender osmolarity and 'mobile sensing' apps for continuous monitoring of various environmental parameters. Moreover, based on a series of experiments under laboratory and field conditions, guidelines for optimizing the dilution process, and time and temperature management during boar semen processing, have been developed and implemented. Similarly, recommendations for the handling of semen doses during storage have been renewed. Over the years, the efficiency of the quality assurance system has been reflected by a decrease of bacterial contamination and a concomitant increase in the quality of semen doses. In conclusion, science-based quality assurance is an effective way to improve the production performance in pig AI centers, resulting in high quality and economically-priced semen for pig producers. Increasing knowledge of sperm physiology together with computational and technical innovations will continue to develop and modify quality assurance concepts in the future.

Post-cervical artificial insemination in porcine: The technique that came to stay

The porcine industry is of great importance worldwide, and so any technological innovation in one or more of the associated production areas is of interest for meat production. Among such innovations in the reproduction area, post-cervical or intrauterine artificial insemination (PCAI) has emerged as a new approach in artificial insemination (AI). PCAI is gradually replacing traditional cervical insemination (CAI), particularly in countries with intensive pig production industries. This type of insemination, which deposits the semen in the body of the uterus (as opposed to traditional cervical deposition), is increasingly used in the field due to its simplicity and the numerous advantages that it provides at production level (e.g. reduced number of sperm, less time required to perform insemination and faster genetic improvement) and, consequently, from an economic point of view. In addition, since its inception, PCAI has been combined with other reproductive biotechnologies, such as the use of frozen-thawed sperm, fixed-time AI or sperm-mediated gene transfer. However, despite its wide acceptance and application, new approaches for increasing the efficiency of PCAI are constantly being sought, such as the adjustment and standardization in sperm numbers, the conservation of the PCAI semen dose, its association with other biotechnologies (sex-sorted sperm) or its efficacy in young (nulliparous and primiparous) females.

A new device for deep cervical artificial insemination in gilts reduces the number of sperm per dose without impairing final reproductive performance

Background

The aim of this study was to evaluate the reproductive performance of a new artificial insemination (AI) device specifically designed for gilts (Deep cervical AI, Dp-CAI) by means of which the sperm is deposited deeply in the cervix (8 cm more cranial than in traditional cervical insemination-CAI). New AI techniques have arisen in recent decades in the porcine industry, such as post-cervical artificial insemination (PCAI), which involves depositing the sperm in the body of the uterus [through a catheter (outer tube)-cannula (inner tube)] rather than by CAI. Although the PCAI method has been successfully applied in farm conditions to reduce sperm doses without impairing the reproductive performance, this technique has limitations in gilts mainly because of the difficulty involved in introducing the inner cannula through the cranial part of the cervix. For this reason, the Dp-CAI method described herein may be considered as an alternative to CAI and PCAI methods in gilts.

Results

Gilts were divided in two experimental groups: 1) Dp-CAI: gilts (n = 1166) inseminated using 1.5 × 10⁹ sperm/45 mL; 2) CAI (as a control group): gilts (n = 130) inseminated using 2.5 × 10⁹ sperm/85 mL. The Dp-CAI method was successfully applied in 88.90% of the gilts, with no differences detected between gilts with 1 or 2 previous oestrus cycles, although the catheter could be introduced more deeply in 2 oestrus gilts (P < 0.05). As the length of the insemination device that could not be introduced increased (at the moment of insemination), so the success rate of the Dp-CAI device fell, as did the total number of piglets born. When the reproductive output in CAI and Dp-CAI was compared, none of the parameters analysed [pregnancy and farrowing rates (%), and number of piglets born (total and live)] showed significant differences.

Conclusions

The use of the Dp-CAI technique provides a new AI method as an alternative to CAI and PCAI for pigs. The device, especially designed for gilts, was used with a high degree of success reducing conventional sperm doses without impairing reproductive parameters.

Electronic supplementary material

The online version of this article (10.1186/s40104-019-0313-1) contains supplementary material, which is available to authorized users.

Removal of seminal plasma prior to liquid storage of boar spermatozoa: A practice that can improve their fertilizing ability

Seminal plasma (SP) plays a vital role in the maintenance of sperm function and integrity along with being involved in their communication with the female reproductive tract. Under in vitro conditions, although it is generally accepted that boar semen is better preserved when SP is diluted (extended) or removed (cryopreserved), its role during storage is not completely elucidated. In this context, the current study sought to determine the role of SP during storage of boar spermatozoa at 17 °C for 72 h. Thus, two treatments were prepared with semen from the sperm-rich fraction (SRF) of boar ejaculate previous to storage in liquid state: 1) PSP: semen directly extended in Beltsville Thawing Solution (BTS), and 2) ASP: semen first centrifuged with subsequent removal of supernatant (containing SP) followed by suspension of sperm in BTS. From this, two experiments were conducted separately in this work: 1) in vitro and 2) in vivo assays. The former aimed to evaluate how sperm capacity responds to in vitro capacitation (IVC) and whether their quality is affected by previous exposure to SP. In the latter, the objective was to understand how important these previous conditions can be for reproductive performance after artificial insemination (AI). According to our results, the previous removal of SP does not affect sperm quality and the response of these cells to IVC (P > 0.05) along with resulting in a lower percentage of acrosome damage in them [12.87 ± 0.76 (ASP) vs. 16.38 ± 0.73 (PSP)] (P < 0.05). This improved preservation of acrosome integrity in the absence of SP can explain the higher fertility rate (%) [63.27 ± 23.47 (ASP) vs. 38.57 ± 16.30 (PSP)] and number of implanted embryos at 28 days after AI (13.71 ± 4.88 (ASP) vs. 7.16 ± 4.02 (PSP)] (P < 0.05) presented by gilts inseminated with seminal doses of ASP. In conclusion, removal of SP prior to liquid storage of boar sperm for 72 h can be beneficial for their fertilizing ability.

Effect of numbers of sperm and timing of a single, post-cervical insemination on the fertility of weaned sows treated with OvuGel®

Variability in estrus and ovulation requires multiple inseminations during estrus to ensure one AI occurs close to ovulation. Induction of ovulation after weaning improves synchrony of ovulation and allows for fixed time AI. However, the interaction between number of sperm in the AI dose and the timing of insemination has not been fully investigated. The objective of this study was to determine the effects of sperm numbers used in a single post-cervical insemination (PCAI) and the timing of insemination following induced ovulation in weaned sows. The experiment was performed using sows (n = 641) allotted by parity (1-6) and lactation length (19.5 d) to receive a single PCAI using 1.5 or 2.5 billion motile sperm at either 22, 26, or 30 h following administration of a GnRH agonist, triptorelin acetate (OvuGel^®) at 96 h post-weaning. Sows received boar contact once daily 3-6 d following weaning. A sub-population of the sows (n = 499) were assessed for follicle size and ovulation utilizing ultrasound at 8 h intervals. There was no interaction of number of sperm and timing of insemination for any response measure (P > 0.10). Wean to estrus interval (4.8 d), duration of estrus (1.9 d), and expression of estrus (88.0%), were not different among treatments (P > 0.10). Of sows scanned by ultrasound at the time of OvuGel^®, 88.2% had large follicles, 10.9% had small, medium or cystic sized follicles, and 0.9% had corpora lutea. The proportion of sows that ovulated averaged 94%, and differed by time of AI (P ≤ 0.05) but not by number of sperm. Pregnancy rate and farrowing rate tended to be affected by dose (P ≤ 0.10), while time of insemination affected pregnancy rate and tended to influence farrowing rate (P ≤ 0.10). Farrowing rate was greater (P < 0.0001) with use of 2.5 than 1.5 billion sperm and insemination at 22 and 26 h compared to 30 h after OvuGel^® (P ≤ 0.10). Farrowing rate was also affected by parity, estrus expression, ovulation and ovarian abnormalities (P < 0.05). Of the 12% of weaned sows that did not exhibit estrus, approximately 50% farrowed a litter. Total born and born alive were affected by dose (P < 0.05) but not time of insemination with both measures increased with 2.5 compared to 1.5 billion sperm (P < 0.05). The results of this study indicate that induction of ovulation in weaned sows resulted in 88% of sows ovulating within a 24 h period. Fertility was improved with a single, fixed time AI using 2.5 compared to 1.5 billion motile sperm and insemination at 22-26 h after OvuGel^® compared to 30 h.

Will AI in pigs become more efficient?

AI is commercially applied worldwide to breed pigs, yielding fertility outcomes similar to those of natural mating. However, it is not fully efficient, as only liquid-stored semen is used, with a single boar inseminating about 2000 sows yearly. The use of liquid semen, moreover, constrains international trade and slows genetic improvement. Research efforts, reviewed hereby, are underway to reverse this inefficient scenario. Special attention is paid to studies intended to decrease the number of sperm used per pregnant sow, facilitating the practical use of sexed frozen-thawed semen in swine commercial insemination programs.