Assisted reproductive techniques for canines: preservation of genetic material in domestic dogs

Rising trends in the use of frozen dog sperm: a retrospective study in Belgium and the Netherlands

Introduction

Sperm cryopreservation is a valuable technique for storing valuable canine genetics. However, little is known concerning the fate of frozen sperm stored in a sperm bank. This study aimed to characterize dogs presented for sperm cryopreservation and describe the use and popularity of frozen sperm in the Netherlands and Belgium over recent years.

Methods

Medical records from dogs presented for sperm cryopreservation between January 1, 2014 and December 31, 2022 at two different freezing centers were reviewed retrospectively. Imported frozen sperm was excluded due to lack of usage information. Each sperm cryopreservation was considered a single event, and data were collected separately for each cryopreserved sample.

Results

A total of 3,090 ejaculates from 1,040 males of 157 different breeds were included and investigated using exploratory data analysis. The findings showed a steady rise in the popularity of sperm cryopreservation, with annual growth rates ranging from 8.4 to 41.9%. The majority of dogs (88.5%) were between 1 and 9 years old at the time of sperm cryopreservation, with nearly one-third aged 2-4 years. Most dogs were collected for sperm cryopreservation once (62.8%) or twice (21.6%). Sperm banks were used for both short- and long-term storage needs, and 6.83% of ejaculates were eventually discarded. The primary use of froze sperm was for international shipment, while 21.8% was used locally for artificial insemination. Depending on the year of cryopreservation, between 44.1 and 79.6% of frozen ejaculates remained unused or only partially used at the time of data collection.

Discussion

The results of this study provides the first comprehensive analysis of the use and popularity of frozen sperm among dog breeders in Belgium and the Netherlands and suggest a change in breeding practices in recent years. The percentage of breeders resorting to sperm cryopreservation and the extent of frozen sperm use in current breeding strategies remain to be defined in future studies.

Flavone and 3-hydroxyflavone supplementation in cryopreservation medium protects canine sperm against apoptosis and lipid peroxidation

Cryopreservation is a pivotal technique in safeguarding genetic material across diverse species, despite its inherent challenges linked to induced spermatozoa damage, notably apoptosis and lipid peroxidation (LPO). Given the insufficient antioxidant defense of spermatozoa against LPO, there is a rising interest in integrating additional additives into extenders to ameliorate mammalian semen quality. Among these additives, flavonoids have garnered considerable attention due to their potent antioxidative properties. Hence, our study aimed to assess the efficacy of flavone (FL) and 3-hydroxyflavone (3-OH = ) supplementation in the cryopreservation medium to protect canine sperm against the damaging impacts of freezing and ensure the preservation of their reproductive potential. Semen was collected from five Beagle stud dogs and then pooled. Then, the sample was divided into 7 groups, each treated with 1) 0 mM, 2) 0.1 mM FL, 3) 0.2 mM FL, 4) 0.4 mM FL, 5) 0.1 mM 3-OH = , 6) 0.2 mM 3-OH = , 7) 0.4 mM 3-OH = . Semen samples were subjected to cryopreservation in French straws and glycerol as a cryoprotectant. In the frozen thawed semen, sperm motility parameters by CASA system and sperm membrane integrity, acrosome status, mitochondrial activity, DNA fragmentation, early apoptosis with capacitation, and LPO were assessed using flow cytometry just after thawing (0 h) and 4 h post thaw. Results reveal significant increase in the proportion of live spermatozoa with undamaged acrosomes in the FL 0.1 and 3-OH = 0.2 groups at 0 h post thaw. At this time point, 3-OH = 0.1 significantly reduced the DNA fragmentation index (DFI) compared to the FL 0.1 and 0.2 groups. However, after the next 4 h, 3-OH = 0.4 exhibited the lowest (P < 0.05) DFI compared to FL 0.2 and 3-OH = 0.1. Additionally, 3-OH = 0.4 showed the highest (P < 0.05) proportion of non apoptotic and non capacitated spermatozoa compared to FL 0.1 0 h post-thaw. Simultaneously, the same group demonstrated significant reduction in apoptotic and capacitated sperm cells, at 0 h and 4 h post-thaw. Moreover, 3-OH = at 0.1 (0 h and 4 h) and 0.2 mM (4 h) significantly enhances the proportion of live sperm without LPO post thaw. Whitin the FL groups, only 0.4 FL significantly increased the percentage of live sperm without LPO. No significant effect of the tested substances was observed on sperm motility, cell membrane integrity, or mitochondrial activity. These findings highlight the promising role of flavone and 3-hydroxyflavone in enhancing sperm resilience during cryopreservation, suggesting their protective function against acrosome damages, capacitation, apoptosis and lipid peroxidation.

Effect of Trehalose Supplementation in Egg-Yolk-Free Extender on Conventional Parameters and Gene Expression Related to Reactive Oxygen Species, Apoptosis, and Motility of Frozen Dog Spermatozoa

The present study was conducted to evaluate the effects of trehalose supplementation in egg-yolk (EY)-free tris extender on dog spermatozoa. Pooled spermatozoa were diluted with extender 1 (EY-free tris extender supplemented with 0, 10, 15, 20, or 30 mM trehalose) and cooled (2 × 108 sperm/mL) for 1 hour at 4°C. After that, extender 2 (extender 1 containing 1 M glycerol) was added (v:v) to the diluted sperm, loaded in 0.5-mL straws (1 × 108 sperm/mL), and incubated at 4°C for 30 minutes. The sperm straws were frozen over liquid nitrogen (LN2) vapor for 20 minutes and then plunged directly into LN2. After thawing at 37°C for 25 seconds, sperm progressive motility (CASA), viability (SYBR-14/PI), apoptosis (Annexin V/PI), and reactive oxygen species (ROS; H2DCFDA/PI) were evaluated. Thereafter, the optimal concentrations of trehalose were selected, and the gene expression of BAX, BCL2, NOX5, SMOX, OGG1, and ROMO1 was evaluated after freeze-thawing. Supplementation with 20 and 30 mM trehalose significantly increased sperm progressive motility and viability compared to the control. However, trehalose had no significant effect on sperm ROS or phosphatidylserine translocation index. There were minor numerical increases and decreases in gene expression when the selected optimal concentrations of trehalose (20 and 30 mM) were compared to the control. However, there were no significant differences. We conclude that the addition of trehalose (20 and 30 mM) in EY-free extender could improve sperm motility and viability without significant effects on ROS, apoptosis, or gene expression.

Effects of different cryopreservation methods on canine isolated preantral follicles

The aim of the present study was to compare the survival and developmental rate of canine isolated preantral follicles (PAFs) after cryopreservation with different methods (closed vs open vitrification). Follicles were isolated from ovaries randomly divided into three groups: fresh control, OPS (open pulled straw) vitrified and cryotube (CT) vitrified. Post-thaw viability of follicles and oocytes was assessed. Fresh and vitrified/thawed PAFs were cultured in 20 µl drops of FSH-supplemented medium for 10 days. Follicular growth, survival rate, estradiol production and ovulation rate were examined. CT method resulted in lower rate of live cells (58.7%) and oocytes (38.8%) than that of fresh ones (83.6% and 64%, respectively) and OPS (80.3% and 79.3%, respectively). Survival rate was similar to fresh follicles in OPS group (98.5% and 95.4%, respectively), while CT decreased the survival to 81.2%. Fresh follicles showed continuous growth, while CT follicles stopped to increase their size after 2 day. In the OPS vitrified follicles, this halting occurred between Day5 and Day10. Fresh follicles showed the highest estradiol production (range: 26.9 - 266.2 pg/ml). Comparing the two vitrified groups, lower estradiol concentration range was measured in the CT group (7.8-48.7 pg/ml vs. 15.4-89.6 pg/ml). Ovulation rate in each group was lowest in the OPS group (1.7% vs 7% and 8.9% in fesh and CT, respectively). Our data show that OPS vitrification provides superior survival rate, in vitro growth and hormonal production to CT. To our knowledge, these are the first results on comparing different cryopreservation protocols on canine isolated preantral follicles.

Effect of Procyanidin on Canine Sperm Quality during Chilled Storage

Procyanidin (PC) is a polyphenolic compound with antioxidant activity. The purpose of this study was to determine the influence of PC on canine sperm quality after 72 h of storage at 4 °C. The collected ejaculates were separated into four equal aliquots and treated with various concentrations of PC (0, 10, 30, and 50 μg/mL) in Tris-citric-fructose-egg yolk (TCFE) extender and stored at 4 °C for 72 h. The findings revealed that 30 μg/mL PC was the optimum concentration for significantly improving sperm motility (p < 0.05). Sperm samples treated with 30 μg/mL PC had substantially greater plasma membrane integrity, acrosome integrity, and mitochondrial membrane potential than the control group (p < 0.05). Furthermore, T-AOC and the expression levels of superoxide dismutase 1 (SOD1), catalase (CAT), and glutathione peroxidase 1 (GPx1) genes were significantly higher in sperm treated with 30 μg/mL PC than those in control (p < 0.05). In summary, this study discovered that adding PC to the TCFE extender enhanced sperm quality and that 30 μg/mL PC was the optimal concentration for canine sperm when stored at 4 °C.

Trends in Small Animal Reproduction: A Bibliometric Analysis of the Literature

Simple Summary

Reproduction in small animals is an expanding research area, with focus on breeding improvement and clinical management of domestic carnivores. The aim of the present study was to conduct a bibliometric analysis of the literature of the last decade on small animal reproduction, to point out main sources, most prolific countries, and emerging and neglected topics. Results show that research in biotechnologies for assisted reproduction has a central and increasing role in this field. Diversity in author keywords was also pointed out and a consensus to better categorize research in this field is proposed to reduce this problem in the future.

Abstract

Small animal reproduction (SAR) is a main research field in veterinary medicine and bibliometric analyses are useful to investigate trends in specific research areas. The objective of the present study was to conduct a bibliometric analysis of the literature of the last decade on SAR. A search equation was created, and documents were retrieved from the Web of Science database. Documents were manually revised, categorized and R software version 4.1.2 with Bibliometrix R package version 3.1 and MS Excel were used to perform the analyses. The included documents (n = 1470) were mainly research articles (78%). The top countries for the number of documents and citations were Brazil, United States, Italy, Poland, and Korea. These also account for the most prolific authors and institutions. Analyses by author keywords, categories, and recent reviews of the literature suggest that research on the canine species is more abundant than research on the feline one and that reproductive biotechnologies are a main research focus. Some clinical topics are still considered niche or neglected themes (e.g., semen collection in tomcats, neonatology). However, heterogeneity and ambiguity in keywords and categories are undeniable. This study offers interesting insights, providing definitions for main keywords in the field of SAR.