In 29 years of semen evaluating bulls I have come across many tricks of the trade to make this procedure run smoothly. This article will hopefully give your local veterinarian as well as purebred breeders and commercial cattlemen some tips they can use at semen-checking time.
Every situation is different and every set of bulls somewhat unique so most of these points involve common-sense and casual observations that I have made over the years.
A common dilemma is simply finding ways to stimulate the bull so you can collect an adequate sample. 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 the 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 initiating better stimulation.
The number of penises that will protrude also increases with proper stimulation. This is important since you need to see the penis to detect problems such as warts, cuts or frenulums (tie backs) so these conditions can be addressed.
A very small percentage of bulls are resistant to the electro ejaculator. For these you may find it worthwhile to put the effort into another collection technique. This involves exposing the bull to a cow in heat and then running the cow into a chute so your veterinarian can suck the semen out of her vagina with a pipette. The semen will be mixed with the cow’s vaginal mucus so the motility will be slowed down a bit so your veterinarian will have to allow for that on the examination.
As a general rule when a bull is hard to collect or doesn’t react to the electro ejaculator this problem will repeat itself in subsequent years so mark this down on his semen form.
Bulls going down in the chute is another common problem, especially with quiet show-type bulls. Leaving their heads free and minimizing the squeeze restraint put on them may help. A bar or post placed behind these bulls is usually enough to keep them in place and upright 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. As a safety precaution with mature bulls I will often set 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 very easy to stimulate and one must watch that you don’t overstimulate them or do it too quickly. Ejaculators with automatic programs may need to be put on manual so the stimulation can be increased gradually. This is where observation and experience will yield great benefits in the successful collection of a semen sample.
A bull that won’t protrude its penis will be difficult to stimulate. However many of these bulls will ejaculate in the sheath and the semen can be milked out by massaging the sheath and collecting it as it runs out. These bulls must be observed at their first mating to make sure there is no physical impairment to the penis extending.
On rare occasions you run across a bull that will consistently urinate in the sample. I have found it helps to give them a rest (say one hour) followed by quick stimulation. This often results in a successful collection. As with other problem bulls, urinators often repeat this same trick in subsequent years.
Stagnant semen with a high percentage of dead sperm can show up in bulls during the winter and anytime they are not actively ejaculating. When you are evaluating pens of bulls this result is definitely more common among the more mature males. In terms of the pecking order you will find the greatest incidence of stale semen in the most dominant bulls and the least dominant ones. My theory is the dominant bulls have nothing to prove so they don’t ride the others and the least dominant bulls are the ones being ridden. Either way they are not ejaculating so the semen becomes stagnant.
These bulls may need to be ejaculated two to three times in succession to get the old semen out of their system before you get a valid sample. The quality should improve drastically in these subsequent samples if this was the problem. Veterinarians can usually tell by the type of morphologic defects (sperm cell defects) if a sample is stagnant or not. A good management procedure is to have cycling cows close by before you start semen testing to get the bulls active.
With the very minute amount of electricity required to stimulate bulls any disruption in this current will cause a failure. For that reason it is very important to maintain this equipment. In particular the electrical ends should be replaced as soon as they become worn and the contact points must be cleaned regularly to ensure a smooth stimulation.
Semen collection is as much art as science. An experienced veterinarian will use all this knowledge to ensure a successful evaluation. Bulls will still fail the test because they don’t measure up but we want to ensure that he is given as fair an evaluation as possible.