In the past 32 years of semen evaluating bulls I have come across many tricks of the trade to make this procedure run smoothly.
Every situation is different and every set of bulls unique so most of these points involve common-sense observations that I have made over the years.
Collecting an adequate semen sample from a bull that is hard to stimulate is a common problem. More often than not the rectal probe is too small so there is not enough contact between the probe and the urethral muscles. This is especially true in very large bulls. You can often increase the amount of contact simply by lifting up on the back of the probe as the bull is being stimulated. This pushes the front of the probe down onto the muscles. This extra contact usually results in more of the penis protruding from the sheath so it is also easier to detect any warts, cuts or a frenulum (tie-back) that needs to be addressed.
A very small percentage of bulls are still unresponsive to the ejaculator. If it is deemed that they are still worth testing they can be bred to a cow in heat and have your veterinarian draw the semen out of the vagina using a pipette. This semen will be mixed with the cows vaginal mucous so its motility will be slowed a bit when your veterinarian examines it. Generally bulls that are hard to collect or resistant to the electro ejaculator will repeat this behaviour in subsequent years so mark that down on the semen form.
A bull going down in the chute is another common difficulty. It seems to happen more often with the quiet show-type bulls so leaving their heads free with only light squeeze restraint or tying their head up with a halter may help keep them up. But usually placing a bar or post behind the bull is enough to keep him secure and standing 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 measure 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 are easier to stimulate. In fact I have to watch I do not overstimulate these bulls, or do it too quickly. Ejaculators with automatic settings may need to be put on manual so the stimulation can be increased gradually. This is where experience can yield great benefits. When the penis does not protrude the bull is difficult to stimulate and many will ejaculate in the sheath but it is still possible to get the sample. Just stop the stimulation and massage the sheath, then collect the semen as it runs out. These bulls will have to be observed at their first breeding to make sure there is no physical impairment. Your vet may want to tranquilize them to make sure the penis can protrude.
On rare occasions you may come across bulls that consistently urinate in the sample. In these cases I have found some rest (say one hour) followed by quick stimulation often results in a successful collection. Again, these bulls will often repeat this trick in subsequent tests.
Stagnant semen, which means it has a high percentage of dead sperm, can show up in bulls during winter or whenever they are not actively ejaculating. In a pen of bulls it is more common among mature bulls. In particular the greatest incidence seems to be found at either end of the pecking order. My theory is the dominant bulls have nothing to prove so don’t ride and the least dominant bulls are the ones being ridden. In either case ejaculation does not occur and the semen becomes stagnant. 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.
More from the Canadian Cattlemen website: Droplets: A common defect in young bull evaluations
Veterinarians can often tell if a sample is stagnant or not by the type of sperm cell defects they find. They may also want to retest when the defect numbers are too high. A good management tip is to have cycling cows close by before semen testing to get the bulls more active.
Only minute amounts of electricity are used to stimulate bulls so any disruption in this current can ruin the process. One sensible precaution is to regularly clean the electrical ends on the probe and replace them when they become worn.
An experienced veterinarian gives you the best opportunity for a successful evaluation but even in experienced hands some bulls will fail because they should. What you want is to ensure that each bull is given the fairest test possible.