Common pitfalls of semen evaluation

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In the past 31 years of semen evaluating bulls, I have come across many tricks of the trade to make this procedure run very smoothly.

Every situation is different and every set of bulls somewhat unique so most of these points involve common-sense and casual observations I have made over the years.

A common dilemma is bulls which are hard to stimulate and collect an adequate semen sample from. More often than not the rectal probe is too small and there is not enough contact made between the probe and the urethral muscles. This is especially true in very large herd bulls.

You can increase contact by lifting up on the back of the probe as the bull is being stimulated. This pushes down the front of the probe, increasing the contact and initiates better stimulation. The percentage which will protrude, also increases. This is very important as visualization of the penis detects problems such as warts, cuts or frenulums (tie-backs) and these conditions can then be addressed.

There is still a very small percentage of bulls refractory to the electro ejaculator. For bulls still unable to be stimulated, it may be worth it to put the effort into another collection technique. This would involve having the bull breed a cow in heat with your veterinarian present. The cow can then be run in and the semen sucked out of her vagina using a pipette and examined.

This semen will be mixed with the cow’s vaginal mucus so the motility will be slowed a bit when your veterinarian examines it. Generally if a bull is hard to collect or refractory to the electro ejaculator, this problem will repeat itself in subsequent years so mark that down on the semen form.

Bulls going down in the chute is a common problem, especially with quiet show-type bulls, so often leaving their heads free with not much squeeze restraint put on them may help in this regard. Tying their head up with a halter may also accomplish keeping them up. A bar or post placed behind the bull is enough to keep them ahead and often the bulls will stay up long enough to collect a sample. This is especially true of large herd bulls. Confinement in a sturdy alley may be easier than trying to hold their heads in a headcatch.

Safety measures

As a safety with mature bulls I will often have a bar behind them in case they get their head free. In hydraulic chutes I leave the back door slightly closed so if they pull their head free they won’t back over me.

I find certain breeds such as Angus and Simmental to be very easy to stimulate and one must watch to not overstimulate them or do it too quickly. The ejaculators with automatic programs may need to be put on manual so the stimulation can be gradually increased. This is where observing and using one’s experience will yield great benefits on the successful collection of a semen sample. If bulls don’t protrude their penis they are difficult to stimulate. However many of these bulls will ejaculate in the sheath and the semen can be milked out by ending stimulation and massaging the sheath and collecting the semen when it runs out.

These bulls will have to be observed at their first breeding to make sure there is no physical impairment to the penis extending or your vet may tranquilize them to make sure they will protrude the penis.

On rare occasions bulls will consistently urinate in the sample. These bulls I have found with some rest (say one hour) followed by quick stimulation will often result in a successful collection. Again the bulls which are urinators will often repeat this same trick in subsequent years as well.

Stagnant semen (high percentage of dead sperm) can be present in bulls in winter and at other times when they are not actively ejaculating. In pens of bulls it is definitely more common in the more mature bulls. With pecking order the most dominant bulls and least dominant bulls seem to have the greatest incidence of this condition. My theory is the most dominant bulls have nothing to prove so don’t ride and the least dominant bulls are the ones being ridden. In each case ejaculation does not occur and the semen becomes stagnant and dead.

These bulls may need to be ejaculated two to three times in succession to get this old semen out of their system. Subsequent sample quality should improve drastically if this was the only problem. Veterinarians can often tell by the type of morphologic defects (sperm cell defects) if the sample is stagnant or not but have to retest if the defects are too high. A good management procedure is to have cycling cows close by before semen testing, as this will get the bulls active.

Because of the minute amount of electricity required to stimulate bulls, any disruption in this low current flow will cause the stimulation process to fail. It is very important the equipment be maintained and the electrical ends be replaced as they become worn. The contact points must be cleaned and a smooth stimulation will result.

Semen collection is as much an art as a science. An experienced veterinarian will use all this knowledge to ensure as successful an evaluation as possible. Bulls will still fail because they should but we want to ensure that no outside forces will make a fair evaluation impossible.

About the author


Roy Lewis practised large-animal veterinary medicine for more than 30 years and now works part time as a technical services veterinarian for Merck Animal Health.



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