Deep-Freezing of Semen in Different Species | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Introduction

Semen freezing is a crucial technique in reproductive technologies, allowing for the preservation and transportation of genetic material. This process varies across species, with bull semen proving relatively easy to freeze, while challenges persist with buffalo and ram semen. Advances in diluents and handling techniques aim to enhance post-thaw fertility, emphasizing the importance of tailored approaches for different species.

Deep-Freezing Semen Across Species

Bull Semen

• Bull semen is relatively easily frozen without significant loss of fertility.
• Plastic straw packing is universally adopted for frozen semen due to automation and labeling convenience.
• While frozen semen is generally considered less viable than liquid semen after thawing, timed insemination close to ovulation helps maintain fertility comparable to fresh semen.
• Tria diluent has been identified as superior for freezing bull semen, but mini straws (0.25 ml) are sensitive to temperature fluctuations and require careful handling.

Buffalo Semen

• Metabolic and biochemical differences between bull and buffalo spermatozoa contribute to the poor survival of buffalo sperm.
• Positive correlations exist between cold shock resistance and freezability, as well as between alkaline phosphatase enzyme levels and post-thaw motility.
• Citric acid whey was developed as a new diluent for deep-freezing buffalo semen, but Tris yolk glycerol has proven more effective in achieving better results.

Ram Semen

• Despite extensive research on ram semen storage, only partial success has been achieved.
• Storage of diluted ram semen at 5°C beyond 12 hours results in a progressive loss of fertility.
• Regardless of diluent composition, storage temperature, and dilution rate, a significant decline in fertility is expected after 24 hours of storage.
• Successful freezing of ram semen through rapid methods has been achieved, resulting in a lambing rate of 50-60%.
• While acceptable fertility has been reported with specific freezing techniques, a higher rejection rate is noted with deep freezing.
• Fertility challenges indicate the need for larger sperm numbers during insemination to match fresh semen outcomes.

Goat Semen

• Goat semen quality peaks during the breeding season, exhibiting unique characteristics compared to ram semen.
• Seasonal variations in enzyme presence within seminal plasma impact fertility, and double washing procedures improve survival and fertility.
• Despite successful results with frozen semen, achieving routine procedures under field conditions requires further refinement.

Boar Semen

• Preservation of boar semen involves glucose-based diluents with buffering agents, and the pellet technique in rapid freezing has significantly improved fertility.
• Egg yolk's protective effects against cold shock differ from other species, and varying insemination techniques impact conception rates.
• The optimal sperm number, thawing in seminal plasma, and cervical inseminations contribute to successful outcomes in boar semen preservation.

Bear Semen

• Preservation methods for bear semen involve glucose solutions with buffering agents, and rapid freezing by the pellet technique has enhanced conception rates.
• Egg yolk's protective role is less pronounced compared to other species, and optimal sperm numbers are crucial for successful insemination.

Fowl Semen

• Artificial insemination is less common in poultry, where semen is collected through the abdominal wall, diluted, and rapidly used.
• Dilution ratios and insemination frequency impact the success of artificial insemination in fowl semen, with specific dosage recommendations for optimal results.

Challenges in Semen Storage and Insemination Techniques

Semen Storage Challenges

• Despite early promising results, a completely satisfactory method for storing or freezing semen, particularly in fowl, remains elusive.
• Pioneering work by Poige achieved 54% fertility and 71% hatchability with frozen fowl sperm at -79°C, but no perfected method has emerged.

Insemination Techniques

• The technique of insemination requires confirming the female's proper heat, absence of pyogenic infection, and ruling out pregnancy through rectal examination.
• Various methods of insemination include the Vaginal Speculum Method (rarely used) and the more widely adopted Recto-Vaginal Method introduced in Denmark in 1938.

Recto-Vaginal Method

• This method involves a simple apparatus consisting of a glass pipette/catheter, rubber pressure tubing, and a glass syringe.
• The operator lubricates their left hand, introduces it into the rectum to grasp the cervix, and guides the catheter through the vagina to deposit semen into the uterus.

Insemination with Frozen Semen

• For insemination with frozen semen, the process involves thawing and pipetting the semen from ampoules or using an inseminating gun with straws.
• Thawed French straws are loaded into the inseminating gun, ensuring proper preparation to prevent air bubbles and ensure successful insemination.

Optimum Timing and Site for Insemination

• The optimum time for insemination is reported to be from six hours before to six hours after the end of heat.
• Insemination into the cervix or body of the uterus yields better results, with mid-cervix deposition recommended due to antibacterial cervical secretions.

Optimum Spermatozoa Number

• The recommended optimum number of spermatozoa for insemination is around 10 million for liquid semen, doubling for frozen semen in cows.
• In buffalo, higher numbers, ranging from 40 to 50 million spermatozoa, may be required for successful insemination.