Semen contents

A. Semen: Spermatozoa + seminal plasma

B. Sources and relative contribution to semen:

Greatest contribution: In bull: vesicular gland; In boars : prostate and bulbourethral glands

C. Chemical composition of semen:

Bull and ram semen: higher in fructose and sorbitol from vesicular gland; Boar semen: higher in Na and K from prostate gland

 1 Spermatozoa

A. Semen characteristics by species:

B. Size of spermatozoa:

Overall length: 60-70 microns in bull, boar and ram sperm; 50 microns in stallion sperm Head: 8-10 microns long; 4 microns wide; 0.5 microns thick

i.                  Normal morphology:

Structural diagram of spermatozoon

 

A. Head:

a. Nucleus: contain genetic code
b. Postnuclear cap: cover posterior portion of nucleus
c. Acrosome: cover anterior portion of nucleus and contain enzymes as hyaluronidase,corona penetrating enzyme and acrosin

B. Neck (sometimes included in "Tail") Proximal centriole: join head and tail, where head and tail separate during fertilization and in heat-damaged semen

C. Tail:

a. Mid-piece: Mitochondrial sheath: contain enzymes converting energy substrates as fructose into ATP b. Main-piece: Axial filament of 2 central fibrils, 9 pairs of inner fibrils and 9 coarse outer fibrils: its contraction by energy from ATP¡æ tail movement
c. End-piece:

ii.  Abnormal morphology

A. Reduced fertility: From 25% or more abnormal sperm

B. Classification of abnormal sperm:

Morphological abnormalities of spermatozoa identified through examination of semen for quality. 

a. Abnormal heads: asymmetrical, tapering , pyriform, giant, micro and double heads
b. Abnormal tails: enlarged, broken, bent, filiform, truncated and double mid-pieces; coiled, looped and double tails; cytoplasmic droplets (formed on neck during spermiogenesis and usually lost during maturation)

 2 Seminal plasma

A. Function: Serve as buffer, optimal osmotic and nutrient medium

B. pH: nearly 7.0; slightly acidic in bulls and rams; slightly alkaline in boars and stallions

C. Osmotic pressure: similar to blood and physiological saline(0.9% NaCl)

D. Energy substrates: fructose, sorbitol etc

 i. Inorganic ions

A. Major ions: Na+, Cl-, K+; minor ions : Ca++, Mg++

B. K+/Na+ ratio: High in sperm cell and low in seminal plasma

C. Function: Maintain optimal osmotic pressure for sperm survival

ii.  Buffering agents

A. Principal organic ion as buffering agent: Bicarbonate(HCO3-)

B. Source: Vesicular gland

C. Function: guard against change in pH of semen, but not sufficient

iii. Energy substrates

A. Energy substrates: Fructose, sorbitol, glycerylphosphocholine(GPC)

B. Source: Fructose and sorbitol: vesicular gland; GPC: epididymis: uniquely high in semen

C. Metabolism:

a. Fructose: used under anaerobic and aerobic conditions
b. Sorbitol and GPC:used only aerobically
c. GPC: utilized after splitted into choline and glycerylphosphate by an enzyme in female tract

 iv. Other organic compounds

A. Inositol and citric acid: considerably high, but not utilized.

B. Ergothionine: found in boar and stallion semen

 3 Energy metabolism by spermatozoa

Plasmalogen: a lipid reserved within sperm cell: used when other substrates are limiting

A. Anaerobically:Fructose _ 2 lactic acid + 2 ATP (net yield)

B. Aerobically : Fructose _ CO₂ + H2O + 38 ATP (net yield)

C. ATP + H₂O ¢¢ ADP + H₃PO₄ + 7,000 calories /mole

 4 Factors affecting rate of metabolism

A. Measurement of metabolism rate

A. Under aerobic condition: 1). O₂ consumption 2). CO₂ liberation 3) Methylene blue reduction time
B. Under anareobic condition: 1) pH reduction 2) Increase in lactic acid 3) Decrease in fructose

B. Relationship of fertile life to metabolic rate of sperm:

a. Reduced metabolic rate : extend the storage life of semen;
b. Reduced metabolic rate in epididymis: extend life of epididymal sperm
c. Sperm in fresh ejaculate of semen: fertile for a few hours under high rate of      metabolism

i. Temperature

A. High temperature: Inc. metabolic rate and dec. life span of sperm

B. At 50¡É: Irreversible loss of sperm motility

C. At body temperature: Sperm live for a few hours only: due to inc.metabolism

D. Low temperature: Extend fertile life of sperm by dec. metabolism ( when bull semen frozen at -196°C, less than 0.02% of metabolic rate at body temperature): Problems: cold shock and freeze kill

a. Cold shock: 1) Irreversible loss of sperm motility by sudden reduction of semen temperature from 15¡É to 0¡É (critical range), 2) Protecting from cold shock: Slow cooling after addition of lecithin and lipoproteins by diluting with egg yolk or milk diluter

b. Freeze kill: 1) Sperm killed during freezeing and thawing 2) Protected satisfactorily by equilibrating bull semen in a diluter containing glycerol ¡æ Desirable fertility from semen frozen for decades

ii.  pH

A. Higher metabolic rate: From pH of semen near neutrality(7.0), where most enzymes in sperm are most active.

B. Deviations toward alkalinity or acidity: Can reduce metabolic rate, but buffering capacity of diluter is rather important because pH range to be altered without permanent impairment of sperm is narrow

iii.  Osmotic presssure

A. Semen diluted with isotonic diluter maintains maximum metabolic activity

B. Hypo- or hypertonic diluter: Can reduce metabolism but detrimental to sperm

 iv. Concentration of spermatozoa

A. Inc.concentration of sperm ¡æ Inc. K+/Na+ ratio ¡æinhibit sperm metabolism

B. Moderate dilution with buffered, isotonic medium containing fructose, before cooling: Not greatly alter metabolic rate, but extend sperm life

C. Excessive dilution (over 1,000x): Depress motility and metabolic rate

 v.  Hormones

A. Androgens over physiological level: ¡é sperm metabolism

B. Fluid from female tracts: Inc. sperm metabolism; due to estrogen or other factors ¡æ ¡èsperm motility

vi.  Gases

A. CO₂

a. 5-10% partial pressure of CO2: sperm metabolism
b. Epididymal sperm: Long life by high CO2
c. CO2 gassing in diluter: Effective for sperm preservation at room temperature

B. O₂

a. Necessary for aerobic metabolism
b. High level of O2: Toxic
C. Other gases: N2, H2, He: No effects

 vii.  Light

A. Light under oxygen: Produce harmful H₂O₂; Semen should be protected from light

B. H₂O₂ production: Prevented by addition of catalase to diluter

 viii. Antibacterial agents

A. Penicillin and dihydrostreptomycin or neomycin: Used for control of bacterial growth, with no effects on sperm metabolism

B. Antibacterial agents: ¡èsemen fertility from bulls infected with vibriosis

C. Control of bacteria in semen by antibiotics ¡æ Sparing energy substrates: Extend fertile life of sperm