Physical and Chemical Properties of Ejaculated Semen | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Introduction

Artificial insemination, a pivotal advancement in livestock improvement, involves depositing male germ cells in the female genitalia using instruments. Widely embraced by dairy farmers globally, this technique enables efficient use of superior sires, earlier proving of young bulls, and facilitates disease control and improved breeding efficiency.

Physical Properties of Ejaculated Semen

Color, Consistency, Volume, and Density

• The color, consistency, volume, and density are primary physical attributes of semen, varying among different species.
• In bulls, a single ejaculate ranges from 2-10 ml, influenced by breed, age, service frequency, season, and nutritional status.

Sperm Concentration or Sperm Density

• Sperm concentration, expressed as million spermatozoa per ml, averages between 900 to 1200 million in bull semen.
• Various devices, including haemocytometers, are used for sperm concentration determination.

Density Classification

• Semen density is classified as DDD, DD, and D, with DDD indicating high density (900 million sperm/ml or more), DD as satisfactory, and D as poor.

Specific Gravity and Viscosity

• The average specific gravity of whole semen is 1.035, and viscosity increases with sperm concentration.

Motility of Spermatozoa

• Individual spermatozoa exhibit progressive motion aided by tail flagellar movement.
• Motility, graded on a scale from 1 to 5, assesses the collective movement of sperm, with grade 3 and above considered fit for insemination.

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pH of Semen

• pH varies with accessory organ secretions, ranging from 6.5 to 7.8 in freshly ejaculated bull semen.
• pH decreases over time due to fructolysis and lactic acid accumulation.

Chemical Properties of Semen

Fructose Content

• Fructose, a crucial nutrient for sperm, is highest in bull semen at approximately 540 mg per 100 ml.
• Fructose levels may indicate the rate of testosterone secretion.

Other Chemical Constituents

• Lactic acid, a byproduct of fructolysis, is present in bull semen.
• Citric acid, adenosine-triphosphate, ribonucleic acid, and deoxyribonucleic acid are found in various regions of sperm.
• Sperm cells are rich in phosphorus, sulfur, zinc, copper, and iron, particularly concentrated in the tail and midpiece.

Lipoprotein and Histone-Like Proteins

• The sperm head, primarily the cell membrane, consists of lipoprotein and histone-like proteins rich in histidine, arginine, and cystine.

Factors Influencing Semen Quality In Vivo and In Vitro

Genital Tract Conditions

• Catarrhal conditions or orchitis can cause brownish semen, while Pseudomonas aeruginosa infection may result in greenish color.
• Injuries to the penis or prepuce may lead to reddish-colored semen.

Age, Breed, and Size

• The age, breed, and size of the sire are linked to semen volume. Semen volume typically increases with age up to 6 to 8 years, maintaining a relatively consistent level thereafter.

Pathological Conditions

• Pathological conditions in the testes and accessory sex glands affect semen consistency.
• Epididymitis initially causes thinner and less milky semen, while catarrhal conditions of accessory sex glands result in thick, viscous semen. Brucellosis can lead to the presence of large purulent flocculi in semen.

Abnormal Spermatozoa

• Abnormalities in spermatozoa may arise due to developmental defects, diseases, or degenerative conditions.
• Abnormalities may occur in the head, neck, or midsection of the epididymis, seminal vesicles, or as a result of diseases affecting the genital tract.

Inflammation and Presence of Cells

• Purulent inflammation in the genital tract may introduce white blood cells (WBC) in semen.
• Lesions in the penis and prepuce can lead to the presence of red blood cells (RBC) in semen.

Factors Affecting Semen Quality

In Vivo:

• Temperature Extremes and Seasons: Abnormal sperm cells are more prevalent during extreme temperatures, hot seasons, and experimental scrotum insulation. Reproductive infections, diseases, and testicular degeneration are associated with a high frequency of abnormal cells.

In Vitro:

• Temperature Changes: Sudden temperature shifts during semen exposure result in increased dead sperm and higher sperm abnormalities. Excessively high temperatures lead to sperm cell agglutination.
• Mechanical Damage: Cell damage may occur during smear preparation.
• Contamination: Water or chemical contamination can cause a high percentage of dead sperm. Direct sunlight kills sperm, resulting in a high number of dead sperm.
• Shaking and Storage: Undue shaking, especially in partially filled semen tubes, can kill sperm. Enzymes from the acrosome can diffuse during storage, affecting semen concentration.
• Metabolite Accumulation: Metabolites accumulate during storage, potentially drifting the medium towards acidity.
• Seminal Plasma Composition: Seminal plasma contains various elements, including inositol, potassium, chloride, sodium, calcium, phosphate, magnesium, proteins, and hormones. Bull semen includes ascorbic acid, B-complex vitamins, proteins, amino acids, adrenalin, and noradrenalin.
• Evaluation of Semen: Laboratory tests are employed for semen evaluation in artificial insemination. Repeated evaluations across multiple ejaculates are crucial to forming opinions about a bull's suitability. Careful handling during collection, transportation, and examination is essential to avoid erroneous condemnations of potentially valuable bulls.

Semen Quality Assessment: A Comprehensive Approach

Initial Physical Characteristics

• Volume, color, and apparent density are promptly observed post-collection.

Motility Examination

• Microscopic evaluation at 37°C assesses motility.
• Various slides, including hollow ground and chambered slides, facilitate examination.
• Swift examination is crucial to prevent interference from moisture evaporation and spermatozoan activity.

Sperm Concentration Estimation

• Utilizing the Thomas Zeiss Hemocytometer, sperm concentration is determined.
• The count is multiplied by 10,000 to obtain the concentration per cubic centimeter of undiluted semen.

Cold Shock Test

• Exposure to 0°C for 3 minutes determines spermatozoa survival, with more resilient samples indicating higher fertility.

Live and Dead Sperm Percentage

• Special stains, like Eosin B and Fast Green F.C.F., differentiate between live and dead spermatozoa.
• Fast staining and drying under hot air are crucial for accurate results.

Abnormal Sperm Percentage

• Abnormal sperm count, assessed in the same preparation as live-dead count, aids in identifying potential fertility issues.
• A high percentage of normal sperm is essential, with less than 15% abnormalities considered normal.

Storage Evaluation

• Stored samples at 5°C are periodically examined for motility and survival rate over 12-hour intervals.
• Ideal samples maintain longevity and motility during storage, indicating quality preservation.

Metabolic Process Evaluation in Semen: Advanced Laboratory Tests

Methylene Blue Reduction Test:

• Measures dehydrogenase activity in semen.
• Determines the time for semen to decolorize methylene blue under incubation.
• Samples with a disappearance time of 3 to 6 minutes are considered suitable for artificial insemination.

Estimation of Glycolysis Rate:

• Anaerobic incubation tracks fructose decline and lactic acid accumulation.
• Photometric method gauges sperm fructolysis, defining the index of fructolysis as the amount of fructose utilized by 10 spermatozoa in one hour at 37°C.
• Normal bull sperm exhibits an index of fructolysis of about 14 to 20.

Estimation of Oxygen Uptake:

• Determines sperm respiratory activity in the presence of oxygen.
• Expressed as Zos, indicating the oxygen taken up by 10 sperm cells in one hour at 37°C.
• Reported Zos values for bull, ram, and cock semen are 21, 22, and 7, respectively.

Correlation and Final Evaluation:

• Metabolic rates correlated with sperm concentration and motility.
• Correlation with fertility status remains debated.
• Final evaluation considers multiple factors: age, service history, clinical picture, nutrition, and husbandry.
• Proposed standards for artificial insemination include criteria for volume, color, concentration, and motility based on age.

Semen Preservation Techniques

• Room Temperature Preservation (18°C to 25°C): Suitable for short-term storage.
• Refrigerator Temperature Preservation (4°C to 6°C): Provides extended preservation with improved fertility.
• Ultra-Low Temperature Preservation (-79°C or -156°C): Long-term preservation, maintaining sperm fertility and enabling insemination of multiple cows.

Optimizing Semen Storage Conditions: Reducing Spermatozoa Activity

• The primary principle in semen storage revolves around minimizing the motility and metabolic activity of spermatozoa. Achieving this can be accomplished by refrigeration at temperatures between 1°C and 6°C or complete suspension through deep freezing at -80°C to -108°C. 
• The medium employed for dilution and preservation, referred to as a dilator or extender, serves to extend sperm lifespan, furnish energy, and act as a buffer. This buffer maintains the fluid's necessary alkalinity to preserve sperm vitality. The extender comprises various non-toxic ingredients crucial for sustaining and protecting spermatozoa, ensuring their fertility remains intact until used for insemination. 
• A suitable diluent must possess the same osmotic pressure and pH as seminal plasma, exhibit robust buffering capabilities, supply nutrients for both aerobic and anaerobic metabolic processes, and furnish lipoproteins and lecithin to shield sperm cells from cold shock during storage, facilitating prolonged motility and viability.