Color and Appearance

Once the semen is collected, it should be filtered if this was not done during the collection itself. General inspection of the ejaculate should be performed with the naked eye to rule out differences in color or appearance. Semen should be white or grayish-white; other types of colors are supportive of disorders. A semen sample that is blood-tinged and flocculent, with clumps of purulent material, may lead the clinician to suspect possible seminal vesiculitis.³

Samples with a urinelike smell and a yellowish color mean urospermia, defined as the presence of urine in the ejaculate. This disorder can be diminished by centrifuging the extended sample. Hemospermia refers to contamination of ejaculates with blood, and hemospermic ejaculates are reddish in color. Hemospermia can result from a variety of conditions. Trauma to the penis may result in injuries such as bruising, lacerations, and hemorrhage and most commonly involves the urethral process, and the application of rings or brushes to prevent masturbation may also lead to penile/urethral bruising. Tumors can also be considered a cause of hemospermia. Profuse arterial hemorrhage in ejaculates usually results from an idiopathic defect in the urethra that communicates with surrounding corpus spongiosum penis.⁴ As with urospermia, hemospermia can be diminished by centrifugation of the extended sample.

Volume

After collection, the semen should be filtered and poured into a warm and sterile container such as a graduated cylinder or a baby bottle. The receptacle should be able to hold at least 100 ml, but when collecting Draft horses a bigger container may be needed.

The average volume produced by a stallion can be affected by different factors. One such factor is the effect of season. Differences of up to 50% have been reported between the height of the breeding season and the nonbreeding season due to changes in the volume of gel production.⁵ The frequency of collection can also affect volume, because stallions collected too frequently may show a decrease in volume produced. No significant effect should be seen in the great majority of stallions with a collection frequency of less than one ejaculate per 24 hours.⁶ Age affects volume, which will increase from 2 to 16 years of age,⁷ and the length of time that a stallion is teased before ejaculation has also been shown to have an effect on the volume of seminal plasma produced due to an increase of the gel-free fraction.⁸ Clinical conditions such as urospermia, pyospermia, and hemospermia will increase the total volume as well.

Motility

Proper dilution cannot be done if motility is not calculated, because 500 million motile spermatozoa are needed for an insemination. The accuracy of motility determination is enhanced when a proper semen extender is added to the sample before evaluation.⁹ As stated before in this chapter, it is of great importance to have warm all the devices that are going to be in contact with the semen, because any change (cold or warm) can affect motility and lead to inaccurate calculations. All equipment should be clean (disposable if possible). A good microscope is necessary for this evaluation and can be hooked up to a monitor to facilitate visualization. A drop of 5 to10 μl should be placed on a slide for calculation. Thick samples have more than one layer and cannot be reliably estimated. Samples of a higher concentration are usually judged by the human eye as having higher motility;¹⁰ therefore semen should be extended to 25 to 50 × 10⁶spermatozoa per milliliter.

Motility at the edges of the coverslip declines more rapidly than in the center as a result of drying and exposure to air.⁶ Therefore all readings should be taken at the center of the sample. The clinician should also make sure that all fields are free of debris and air bubbles, because they can also affect the outcome. Raw semen should not be used, because agglutination or sticking of sperm cells to the glass will give inaccurate results.¹¹

Concentration

The number of spermatozoa produced by a normal stallion is a function of the testicular size. One gram of testicular parenchyma during the breeding season produces approximately 19 million spermatozoa per day, which decreases to 15 million during the nonbreeding season.¹² The total scrotal width is highly correlated with the testicular weight, size, and sperm production and is therefore regarded as an important consideration when evaluating the potential fertility of a certain stallion’s ejaculate.¹² The amount of sperm produced by a stallion increases with age¹³ because the total length of the seminiferous tubules becomes larger and increases by more than 30% during the life of the stallion.⁶ Most stallions older than 4 years seem to have a similar sperm production per day per gram of testicular parenchyma during the breeding season.⁶ Therefore, because daily sperm production is one factor affecting the number of spermatozoa available for ejaculation, usually more sperm will be ejaculated by older than younger stallions.

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