Evaluating boar semen

Evaluating boar semen is important for making sure the quality and quantity of the sample is satisfactory.

Evaluation of boar semen is rarely needed in small, within-herd AI programs where undiluted semen is used within hours (especially if the boar has a successful impregnation record).

However, if the boar has not previously provided semen, or if the semen is going to be diluted, then evaluating semen viability can be useful.

Volume

• Volume is measured in a warm (34°C), dry calibrated flask.
• Volume is usually 100–500mL (large volumes do not necessarily contain more sperm than smaller volumes).

When used undiluted, the volume determines the number of inseminations possible from each collection. The volume of semen per insemination is 50–100mL.

Motility

• Observing motility is the best way of estimating semen quality.
• Observing motility is not necessary for obviously fertile boars (unless dilution is required for inseminating a large number of sows).

To determine motility, place a sample on a warm slide (30–35°C) immediately after collection and under the low power lens (x50) of a microscope.

A typical 'wave' motion and movement of individual spermatozoa are both indications of good quality semen, whereas 'clumping' and weak motility indicates a poor quality sample. Motility depends on the volume of each fraction collected—higher motility and wave motion is detected in the sperm-rich (second phase) fraction, whereas accessory fluids dilute the semen (resulting in weak motility).

Density

• Accurate estimates are needed only when high dilution rates are used at artificial breeding centres.
• Density depends on the volume of post-sperm faction collected.
• Density varies from 100–500 million spermatozoa per mL (60–80 billion sperm are present in a normal ejaculation.
• Estimates of dead and abnormal spermatozoa are normally only performed at artificial breeding centres.
• Abnormalities include detached heads, bent and returned tails, broken tails, and twin heads or tails.
• Instruments such as the hemocytometer and the spectrophotometer help determine semen density.

Abnormalities

The presence of immature spermatozoa (which show protoplasmic droplets on their tails) indicates that a boar has been overworked. If the total abnormalities detected in a sample are less than 25%, then the quality of the semen is classified as 'satisfactory'.

Measure to manage

Record the results of all measurements to enable collection and processing procedures to be reviewed, evaluated and improved.