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A Guide to Basic Boar Semen Collection, Evaluation
and Processing Procedures

Wayne L. Singleton

Department of Animal Sciences
Purdue University
West Lafayette, IN 47907


There are numerous methods available for processing semen which utilize various equipment items and techniques. Always keep in mind the two basic principles of semen collection and processing. (1) Use hygenic techniques and (2) control temperature changes. For the most part, if these principles are followed, specific techniques and equipment, which are used, become a matter of economics, ease of maintaining quality control and personal preferences.

Since there is some risk of lowered reproductive efficiency associated with an A.I. program, investment in proper training and equipment is an important consideration. The following description outlines a technique for a basic on-farm program where typically semen from less than 4 or 5 boars is collected and processed on a weekly basis. As the number of boars and collections increase, one should consider other techniques which may decrease the total cost of producing a unit of semen or improve the quality control process.

Equipment Requirements

Major Itemsa
Cost (range)

Microscope (10x eyepiece with 10 and 43x objectives)

Digital scale (6 kg ± 1 gm)

Semen cooling unit

Assorted glassware, plasticware, thermometers, gloves, thermos, etc.

Warming cabinet

Adequate dedicated workspace, i.e., clean, dry, temperature controlled

Water bath

Sperm counting equipment

a Assumes a bottle and cap packaging system.


Get Ready

Line a 1 liter insulated collection container with a plastic bag. One gallon freezer bags work well for this. Insulated containers and plastic bags are available from A.I. equipment suppliers. Place filter (double layer of cheese cloth or one commercially available filter) over container and secure with rubber band. Provide a means for recording boar I.D. (i.e., tape or label).

Pre-warm semen collection container. Suggestion: Line a section of a cabinet with styrofoam insulation. Install a light bulb wired to a thermostat. Set thermostat at 38 C. Store all equipment used for collection and processing in this cabinet. It provides a warm, dry, and dust free storage area. If used correctly, it can substitute for a water bath.

Record an empty weight for each collection container (with lid) and bag. As long as no major changes are made, this will remain rather constant from day-to-day, but check it on occasion.

Prepare extender. There are several ways to do this, here is one:

Place pre-warmed semen collection container into a pre-warmed insulated picnic cooler. Suggestion: Purchase a mid-sized plastic picnic cooler that has a plastic container which fastens to the inside of the lid. Fill this flat container with warm water (38-42 C) depending upon environmental temperature. This container should provide a temperature of about 37 F at the site of boar collection. Cut a piece of thick styrofoam (2- 4") to fit the bottom of the cooler. Cut holes in this styrofoam to the size of your semen collection containers. This will prevent tipping of containers and provide further protection from temperature changes. Note: If the collection area is adjacent to the processing area, construct a pass-through warming cabinet in the wall which separates the two areas and pre-warm the container here.


Collect Boar

If necessary, squeeze fluid from the "pouch" located near the sheath opening. This should be done before the boar mounts. Avoid contaminating the ejaculate with these fluids. If necessary, clip long hair from sheath area. This should be done about once per month for sanitary reasons and the boar will appreciate it as well.

Collect the boar using poly vinyl gloves, NOT LATEX! Once the glove has been put on your hand, do not touch the boar, gates, or anything else except the boar penis. Some semen collectors prefer to wear double gloves and the outer glove is removed just before the penis is grasped.

Always discard the first part of the ejaculate (pre-sperm). It is clear, watery fluid and does not contain sperm, but it may have a high bacterial count.

Collect sperm-rich fraction into your pre-warmed container. It will be very chalky in appearance and contains 80-90% of all sperm cells in the ejaculate. Collect this fraction until it changes to a more clear, watery fluid. Once you are certain the sperm-rich fraction is complete, continue collecting but discard the remainder (post-sperm) of the ejaculate. Note: Some boars will ejaculate the sperm-rich portion in waves. Be sure to note this. Some persons collect both the sperm-rich and post-sperm fractions which is probably satisfactory, but some suggest that storage time may be reduced when the total post-sperm fraction is included. In practice, a "modified, sperm-rich" fraction will be collected (i.e., sperm-rich and some post-sperm).

Always allow the boar to complete his ejaculation (5-8 minutes). If you let loose too soon, be prepared for a challenge. He will not want to leave the dummy. You will make this mistake only once or maybe twice.

Remove the filter with gel and discard. Cap the collection container and place in warm container ASAP. Be sure to label the container with the boar I.D.

Transport the ejaculate to the processing area ASAP. Attempt to schedule procedures so that the ejaculate is extended within 15 minutes after collection. See Figure 1.


Estimate and Calculate

Weigh the collection container and subtract the tare weight. This will give you the ejaculate volume. Note: Semen is actually slightly heavier than water which weighs 1 gram per ml or cc, but use a 1 to 1 ratio, this is close enough.

Boar Semen Time-Line

Figure 1

Use your microscope to evaluate sperm motility and relative sperm concentration. Always use a pre-warmed glass slide and cover slip. Ejaculates with a progressive motility estimate of less than 60% are generally discarded. Observe for the presence of abnormal sperm and cellular debris and "clumping".

Decide how many bottles (units) of semen that can be processed from the ejaculate. Each bottle should contain about 3 to 4 billion sperm and 80 to 100 ml fluid. The boar ejaculate may contain from a low of 10 to 15 billion up to over 100 billion sperm or enough sperm for 2 or 3 bottles up to 25 or more bottles. This number depends upon age, breed, frequency of collection, and individual boar. If you do not have a sperm counting device, you will have to follow some guidelines. Actually you will make an educated guess. Depending upon relative sperm density (opaqueness) most recommendations are to dilute the ejaculate from 1 part semen to 3 parts extender up to 1 part semen to 10 parts extender. The more opaque and chalky appearing, the higher the possible dilution rate.


Semen volume (gram/ml)

Relative Opaqueness1 Score

Dilution Semen/Extender

Amt. (grams or ml) Semen + Extender

Total Amount of Extended Semen

Number of Bottles
(100 ml each)




150 + 450






150 + 900






150 + 1500



1 3 = watered down milk; 6 = milky; 10 = creamy
2 Since you are not going to inseminate a sow with a half bottle, always round down to nearest full bottle. In this example, add the remaining 50 ml to each of the bottles or add just 850 ml of extender rather than 900 ml (150 ml semen + 850 ml extender = 1000 ml or 10 bottles containing 100 ml each).


Various instruments for estimating the number of sperm cells are available. They include: (a) hemocytometer, (b) spectrophotometer and (c) SpermaQue. Follow the protocol for the given instrument to estimate the number of sperm cells in the ejaculate. Record the appropriate data and calculate the extension rate. (See sample Boar Record form.)


Extending Semen

Cardinal Rules:

1. Adjust extender temperature to within 1° of semen temperature.

2. Always add the extender to the semen.

The plastic bag containing the semen should still be in the collection container. Place a glass thermometer into the semen. Place another thermometer in the extender. Adjust the extender temperature to equal that of the semen. Once a routine is established, you will soon learn when to remove your extender from the warming cabinet or water bath so that it will be very near the semen temperature. The semen will likely be about 35 to 36°C at this time. Note: Check accuracy of thermometers on a regular basis.


Remove a large pre-warmed flask (at least 2 liter) from the warming cabinet. Gently place the bag containing the semen into the flask and push "tare". From the previous example, you estimated that 10 bottles of semen could be processed from the ejaculate and that the total amount of extended semen would be 1000 ml or grams, so add extender to the flask until the scale reads 850 g. 850 g extender + 150 g semen = 1000. See Fig. 2.

Figure 2 - Pour the extender into the flask containing the semen

Figure 2.

Pour the required amount of extender down the side of the flask until the scale reads 850. Gently mix the semen and extender by lifting the bag by its corners. Use your microscope to check motility again.


Most storage containers hold from 80 to 100 ml. Note: Use your scale again. Place an empty bottle on the scale and push "tare". Add 100 grams of distilled water and mark a line with a magic marker. Use this bottle as your template. Gently pour the semen down the side of the empty bottles and fill to this imaginary line. If you have a few ml of semen left, just use it to top off each bottle. Label each bottle with boar I.D., date of collection and other pertinent information.

Use your microscope to estimate motility again. This serves as a quality control step for the whole process.

Assuming the room temperature is about 21°C±, set the bottles on a towel and cover with another towel and let them cool at room temperature for an hour or so. Protect semen (storage containers) from sunlight. Place them into the cooling device which should maintain a temperature of 17-18°C. Gently rotate the bottles twice per day to resuspend the sperm cells. Evaluate and record motility of semen at 24 h intervals.

To achieve the highest farrowing rates and litter size, attempt to inseminate sows with fresh semen (< 24 to 48 hr). Farrowing rate may decline 1 or 2% for each day that semen is stored.

Mixing Semen from Two Boars

If semen from two boars is collected on a given day and a record of parentage of offspring is not important, consider mixing or combining semen from these two boars. This is called "heterspermic insemination" rather than "homospermic insemination."

  1. Collect, weigh and calculate potential number of inseminations from each ejaculate.

  2. Completely extend each ejaculate. Temperature of semen in each bag should be within 1°C. If an adjustment is necessary, slowly cool the warmer bag.

  3. Gently combine the extended ejaculates and package.


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