TABLE OF CONTENTS
Macroscopic Examination of Semen: Naked Eye Assessment of Semen Quality in Animals
Macroscopic examination of semen refers to the visual and physical assessment of a semen sample without using a microscope. It is the first step in semen evaluation and provides quick insights into the general quality and suitability of the semen for fertilization or preservation.
The following parameters are examined during the macroscopic examination of semen:
- Volume
- Colour
- Viscosity and Density
- Presence of Foreign Materials
- Gross Motility
1. Volume
Read from the graduated semen collection vial immediately after collection. Volume remains fairly constant for each species.
Volume varies among individuals and between ejaculates within the same individual. Volume increases with age and body size of animal and changes with general reproductive health and vigour and frequency of service.
Teasing and stewing of bulls are practiced to increase the volume of semen. Semen volume increases up to 6-8 years of age. After that it is maintained for some period and starts declining afterwards.
Decreased semen volume is noticed in following conditions:
- Young males
- Males used excessively
- Incomplete ejaculation or failure of ejaculation
- Bilateral seminal vesiculitis
Volume of Semen in Different Species
Nomenclatures for Different Evaluation Criteria
| Explanation | Terminology |
|---|---|
| No sperm | Aspermia |
| Reduced | Hypospermia |
| Increased | Hyperspermia |
2. Colour
Bull and buck semen is highly concentrated and hence the colour of their semen may be milky white, creamy or opaque. Buffalo semen is whitish when compared to bull semen.
In stallion, boar and dog, the colour of semen is pearly white to grey and translucent.
Any deviation from the normal colour should be suspected for pathological conditions.
Based on colour bull semen is graded as:
- Creamy
- Thick milky
- Milky
- Thin milky
- Watery
Yellow colour of semen is normal in some bulls due to riboflavin content, which is secreted, from ampulla or seminal vesicles.
3. Viscosity and Density
Semen may have various consistencies like creamy, milky or watery. This largely depends on sperm concentration.
Viscosity is assessed by using semen delivery pipettes. Viscosity increases with sperm concentration.
The specific gravity of bull semen is 1.03610.008. There is a positive correlation between specific gravity and sperm cell concentration.
Density gives a rapid assessment of concentration. The score used to express density is ‘D’.
| Colour Density | Grade |
|---|---|
| Creamy | DDDD |
| Milky | DDD |
| Thin milky | DD |
| Translucent and cloudy | DD |
| Watery | O |
Certain pathological conditions of the testes and accessory sex glands may affect semen consistency. Some examples include:
- Epididymitis: less milky semen
- Catarrhal conditions of accessory sex glands: thick viscous semen
- Seminal vesiculitis
4. Presence of Foreign Materials
The foreign materials may enter into the semen from the animal, environment or from AV and will affect the quality of semen.
The following are the materials may be present inside the semen:
- Dung, pus, urine, hair, dust- from animals.
- Sand, bedding materials, dry dung, insects-environment.
- Water, lubricant jelly, dusting powder-AV.
5. Gross Motility
- A drop of semen is place on a warm glass slide and is observed in naked eye.
- A semen sample with good motility will show wavy motion when it is observed.
- Sperms with poor quality will not show wave motion.
- Based on the wavy motion the semen sample is graded.
