This lecture explains the semen and its components in domestic animals useful for veterinary graduates, clinicians and aspirants of IAS, RAS and other examinations.

1. SEMEN AND ITS COMPOSITION
IN MALE DONMESTIC ANIMALS
Prof. Dr. G.N Purohit
MVSC, PhD, MNVAS
Dean Post Graduate Studies and University Head Dept. Veterinary
(Gynecology & Obstetrics)
College of veterinary & Animal Science, RAJUVAS
Bikaner, Raj., India.
Email: gnpobs@gmail.com
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2. About Me : Professor G N Purohit, MVSc, Ph.D, MNVAS
Head, Department of Veterinary
Gynecology and Obstetrics, Veterinary
College, Bikaner, Rajasthan, India
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3. Todays Topic –Semen and its composition
■ <Topic 1>Semen and its components
■ <Topic 2>Spermatozoa and its morphology and
functions of parts of the spermatozoa
■ <Topic 3>Sperm metabolism
■ <Topic 4>Constituents of seminal plasma
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4. SEMEN AND ITS COMPOSITION
■ Semen is a greyish white bodily fluid that is
secreted by the gonads of male animals during the
process of ejaculation.
■ The semen has two components the cellular
component the spermatozoa and the liquid
component seminal plasma.
■ The fraction of the semen made up by spermatozoa
is known as the spermatocrit, and ranges from
more than 30% in sheep to less than 2% in pigs.
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6. Animals produce motile sperm with a
tail known as a flagellum, which are
known as spermatozoa, while some red
algae and fungi produce non-motile
sperm cells, known as spermatia
Spermatozoa
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7. Mature spermatozoa consists of a head, neck and
tail
The sperm head is ovoid to spatulate in most
domestic animals (Hook like in rodents) covered with
a cap the acrosome and contains the nuclear DNA
•The mid-piece consists of a helix of
mitochondria with central 2 and surrounding
9 fibres, which extend into the tail.
The head is continued by a neck, mid-piece and
tail.
Spermatozoa
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9. Biometry of spermatozoa in different species
Species Head (µ) Mid piece (µ) Tail (µ) Total length (µ)
Length Width Length Width Length Width
Cattle 9.05 4.25 14.84 0.67 45.50 0.51 69.59
Buffalo 7.50 4.70 11.95 0.62 42.50 0.50 61.95
Ram 8.20 4.25 14.00 0.80 40.45 0.50 62.65
Buck 8.14 4.30 12.52 0.72 42.77 - 63.43
Boar 8.05 4.18 11.55 0.55 32.94 - 52.54
Stallion 7.00 3.91 9.83 - 42.30 - 59.13
Poultry 12.5 - 4.00 - 80.00 - 96.50
Dog 5.5-7.0
(6.1)
2.0-4.0
(3.8)
7.0-13.0 1.0 40.0-45.0 57.5 - 66.1 (61.4)
Camel 5.5 6.9 35.6 48
Amongst mammals mouse has the longest spermatozoa 124µ,
whereas the spermatozoa of an elephant is 56 µ length.
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10. Nucleas compsed
of densely packed
chromatin
The acrosome covers 2/3rd of
nucleas divided into apical, main
and equatorial segments
The cap like
structure of
acrosome contains
acrosin and
hyaluronidase
The neck is
between the head
and first
mitochondrial spiral
of middle piece
Sperm Head
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11. Functions of the sperm head
■ The head of the sperm contains the DNA, which when
penetrates the oocyte DNA, will result in fertilization and
production of a zygote. The tip of the sperm head is the
portion called the acrosome.
■ The acrosome contains digestive enzymes (including
hyaluronidase and acrosin) which enables the
sperm to penetrate the female gamete-
the oocyte.
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12. Sperm neck (Connecting piece)
■ The sperm neck contains centrioles that
form the cilium (also known as the
flagellum) of the sperm, and after
fertilization form the major microtubule-
organizing center of the zygote.
■ The sperm neck or tail (depending on the
species) also contains the mitochondria
that are used as an energy source.
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13. Sperm Tail (Flagellum)
Middle
piece
Principal
piece
End
piece
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15. Axoneme
Mitochondrial
sheath
Outer Dense
fibers
Fibrous
sheath
Mammalian sperm tail
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16. Axoneme
■ The axoneme is a microtubule-
based structure of nine outer
doublet microtubules and two
central doublets (9 + 2) associated
with radial spokes and dynein
arms. The protein Dynein arms
with Nexin links within the
axoneme provide the motor
apparatus for the movement of the
sperm tail.
■ These extend throughout the
length of the tail.
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18. The outer dense fibers are cytoskeletal structures
that surround the axoneme in the middle piece and
principal piece of the sperm tail.
The fibers function in maintaining the elastic
structure and recoil of the sperm tail as well as in
protecting the tail from shear forces during epididymal
transport and ejaculation
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20. The helically arranged mitochondrial sheath surrounds the outer
dense fibres in the midpiece, whereas only the fibrous sheath
surrounds the outer dense fibres in the principal piece.
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21. Due to the termination of mitochondrial helix in
the midpiece, the diameter of the tail in the
principal piece is reduced.
The principal piece is characterized by the
presence of a fibrous sheath, which provides
stability for the contractile elements of the tail.
The end piece of the sperm tail contains only
the axoneme surrounded by the plasma
membrane
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22. Sperm tail function and motility
■ The sperm tail function to provide motility to the spermatozoa.
■ The mitochondrial helix of the midpiece generate energy in
the form of ATP, which is used for sperm locomotion. The
inner mitochondrial membrane is the site of energy
production. The elongated mitochondrial helix surrounds
approximately 80% of the midpiece. There is a wide range of
variation among mammals in the length of the midpiece and
in the number of mitochondria present.
■ The laminated columns of mid piece give
neck region flexibility allowing for lateral
movement from side to side during flagellar
beating.
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23. ■ To provide energy for motility the sperm must metabolize. The anaerobic
metabolism occurs through glycolysis whereas the aerobic metabolism
occurs through TCA cycle.
■ Sperm metabolism occurs through a series of enzymatic processes, they
produce products that can enter glycolysis to enter TCA cycle to produce
ATP.
■ Both fructose and glucose can be utilized during sperm metabolism. The
ATP is used for sperm motility.
■ Some ATP is wasted in sperm metabolism by
substrate cycling (glucose 6-phosphate to glucose).
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26. ■ The microtubule sliding occurs as a
result of the sliding of the
microtubules (derived from ATP
derived from ATPase); the dynein arm
detaches in the presence of ATP and
shortens; once that energy is made,
the dynein arm tilts and elongates to
attach to a lower side and then
shortens and returns to its original
position; this generates the sliding
forces that move the tail in a helical
fashion.
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29. CHEMICAL CONSTITUENTS OF SPERM
■ The main chemical constituents of spermatozoa are
deoxyribo-nucleoprotein, in the sperm nucleas
■ protein bound muco-polysaccharide, in the acrosome
■ phospholipid in the mid piece and tail
■ keratin –like proteins, which compose the sperm
membrane and fibrils, and
■ a variety of enzymes and co-enzymes which control
the motility and metabolic activity of spermatozoa.
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30. Constituents of seminal plasma
Carbohydrates
■ One of the most remarkable features of semen is that the predominant reducing
sugar is not glucose, as in blood, but fructose.
■ Small amounts of glucose are also present, and boar semen in particular contain
large concentrations of inositol, but less fructose than semen from bulls or rams.
Inositol acts as a osmotic regulator.
■ Stallion semen also contains inositol and lower concentrations of fructose, and
other compounds of inositol are also present in some species. Fructose in bulls and
rams originates in the seminal vesicles, with some from the ampulla, but in the
stallion, most comes from the ampulla. Inositol is secreted in the seminal vesicles.
Fructose is absent in the dog.
■ Both glucose and fructose can be utilized by sperm, either by oxidation
or glycolysis, although the Michaelis constant (Km) for glucose
is much lower than that for fructose.
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31. ■ The mitochondria, in which oxidative phosphorylation
occurs, are arranged as a helix around the midpiece of the
sperm, whereas the glycolytic enzymes are concentrated in
the principal piece of the tail, while some are bound to the
fibrous sheath of the flagellum. However, it is unlikely that
glycolysis alone could generate enough ATP for full motility,
and while diffusion from the mitochondria may be sufficient in
smaller sperm, in larger sperm it is likely that an adenylate
kinase shuttle is involved in moving ATP from the
mitochondria to the flagellum .
■ There is evidence for the occurrence in sperm of specific
glucose transporters that can transport
both glucose and fructose.
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32. ■ Proteins, amino acids and other nitrogen-containing
compounds
Seminal plasma contains a variety of proteins and peptides,
the total concentration being somewhat less than that in blood
plasma
Seminal plasma proteins are derived from the epididymis and
the accessory glands, and are involved in several essential
steps preceding fertilization, including capacitation,
establishment of the oviductal sperm reservoir, modulation of
the uterine immune response, sperm transport in the female
tract and gamete interaction and fusion.
Seminal plasma also contains considerable concentrations of
free amino acids, particularly glutamic acid
in rams and bulls
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33. There are also appreciable concentrations of carnitine in the seminal
plasma of rams, bulls and stallions. This substance is involved in fatty
acid transport in other tissues, but that present in semen is largely
derived from the epididymis. Boar semen also contains
ergothioneine, the betaine of thiolhistidine, a sulfur-containing
reducing base, which comes mainly from the seminal vesicle; it is
also present in stallion semen, but in this species, it originates largely
from the ampulla.
Semen and seminal plasma from rams, bulls, goats, boars and
stallions were found to contain considerable amounts of
glycerophosphorylcholine, which originates largely from the
epididymis , as well as glycerylphosphorylinositol.
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34. Semen contains considerable amounts of lipid, both neutral lipids and phopholipids,
most of which is in the spermatozoa . In ram semen, the most abundant phospholipid
is choline plasmalogen (also known as phosphatidalcholine), whereas in boars, it is
lecithin (also known as phosphatidylcholine) and in bull sperm, the two phospholipids
are present in approximately equal amounts. One remarkable feature of these
phospholipids is their high concentration of highly unsaturated fatty acids, 22 carbons
in length, with six double bonds (22:6) in rams and bulls and five double bonds (22:5)
in boars. These constituent fatty acids are particularly susceptible to damage from
reactive oxygen species. The phospholipids may also be important precursors of
platelet activating factor (PAF), which is probably involved in sperm motility, the
acrosome reaction and fertilization, and which is found in bull and boar sperm.
Seminal plasma from bulls and stallions contains an acetylhydrolase, which may play a
role in regulating autocrine or paracrine functions of PAF.
Semen also contains appreciable concentrations of steroids. In bull semen, the
concentrations of several steroids, including progesterone, dihydrotestosterone,
androstanediols and oestrogens are much higher than in blood plasma. The
oestrogens appear to come from the prostate, whereas the other steroids originate
from the epididymis. Testosterone is present in seminal plasma at about the same
concentration as in blood plasma, much less than in the rete testis fluid leaving the
testis.
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36. Contact me
Prof. Dr. G.N Purohit
MVSC, PhD, MNVAS
Head Dept. Veterinary (Gynecology & Obstetrics)
College of veterinary & Animal Science, Bikaner, Raj.India.
Email:gnpobs@gmail.com
Linked in : linkedin.com/in/dr-govind-narayan-purohit-13a04a17
YouTube Channel link : https://www.youtube.com/user
/gnpobs61/videos
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