You cannot build a good dose without knowing how many sperm you started with. There are two ways to get that number on the farm: count by hand with a hemacytometer, or read concentration from a counting device such as the Quick Check.
The terms
- Total volume: everything collected, in mL (1 cc = 1 mL).
- Gel-free volume: the volume after the gel has been filtered out. Most stallions produce little gel unless something distracted them or went wrong at collection.
- Concentration: sperm per mL of raw semen.
- Total sperm: gel-free volume × concentration.
- Progressive motility: the percentage of sperm moving steadily forward.
- Total motility: slightly motile plus progressively motile. “80/70” means 80% total and 70% progressive.
- Usable sperm: total sperm × progressive motility. This is the number a dose is built on.
Option 1: a hemacytometer
A hemacytometer is a glass slide with two counting chambers. A coverslip rests on pillars exactly 0.1 mm above an etched grid, so the volume over the grid is known.
- Dilute and immobilize the sample. Sperm must be still to be counted. Dilute a measured amount of semen into a fixative diluent and write down the dilution. A 1:100 dilution (0.1 mL semen into 9.9 mL diluent) is a common starting point. About 20 to 25 cells per large square means the dilution is right.
- Load about 15 microliters at the V-shaped groove and let capillary action fill the chamber. Do not overfill it or move the coverslip afterwards.
- Let it settle for 2 to 3 minutes so the cells stop drifting, but not so long that it starts to dry.
- Count. The central area has 25 large squares. Count cells touching the lines on only two sides of each square, so none is counted twice. You can count all 25, or count 5 and multiply by 5. Count both chambers, aim for at least 100 cells, and average them.
- Calculate. The central area holds 0.1 microliters. Count per central area × 10,000 = sperm per mL of diluted sample. Multiply by the dilution to get sperm per mL of raw semen.
Worked example. At 1:100, counting 5 of 25 squares gives 132 and 128 cells in the two chambers. The average is 130, and 130 × 5 = 650 per central area. 650 × 10,000 = 6.5 million per mL diluted, and × 100 = 650 million sperm per mL of raw semen.
Option 2: a counting device
A counter such as the Quick Check reads concentration from a sample of raw semen in a cuvette, in about the time it takes to load it. It is the faster choice when you collect often, and many farms check it against a hemacytometer from time to time.
From count to dose
Exodus’s guideline for a cooled, shipped dose:
- At least 750 million progressively motile sperm, up to 1 billion
- About 25 million per extended mL, and never fewer than 20 million
- At least 5 parts extender to 1 part semen, which keeps seminal plasma at no more than about 20% of the dose
Example. A stallion gives 50 mL gel-free at 200 million/mL with 70% progressive motility.
- Usable sperm = 50 × 200 million × 0.70 = 7 billion
- At 1 billion per dose, that is up to 7 doses
- Each dose holds 1 billion ÷ 0.70 ≈ 1.43 billion total sperm, which is 7.1 mL of raw semen
- At 25 million usable per mL the dose would be 40 mL: 7.1 mL of semen plus 32.9 mL of extender. That ratio is only 4.6:1.
- So take the dose to 43 mL instead: 7.1 mL of semen plus about 36 mL of extender. That is about 5:1 and about 23 million usable sperm per mL, inside both guidelines.
When the raw concentration is low, a stallion may need centrifuging before he can be extended properly. See centrifuging stallion semen.
Adapted from Exodus "Counting Cells with a Hemacytometer", semen terms glossary and extender direction sheet. This guide covers handling and use only; breeding timing, insemination and anything involving medication are for your veterinarian.