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Semen Evaluation — Why Do It?

After all this time there are still some producers sceptical to the merits of having a semen evaluation done on their breeding bulls prior to turnout. There are many benefits to the evaluation, and hopefully I can lay to rest any misconceptions surrounding it.

In performing a semen evaluation veterinarians are really doing much more than just checking the semen. The process is really called a Breeding Soundness Evaluation. The abbreviation is a BSE exam, but that is seldom said anymore since the common reference for mad cow disease is BSE, as well.

With the true evaluation of semen we check both live sperm for motility as well as stained to kill the sperm and look at the sperm morphology, which is the percentage of sperm which are defective. We as veterinarians can see these defects under the microscope at high power (1,000 X). Certain defects are caused from faulty formation and others crop up when the bulls are not very active and the sperm becomes stagnant. These defects result from improper maturation of the sperm.

At the same time the bull is restrained for collection, body condition is assessed and the feet and legs are checked. We can visualize the undercarriage of the bull so what better opportunity to check out the feet and sheath of the bull. Veterinarians observe the bull walking so any structural defects are also picked out.

A big part of any evaluation is the measurement of the scrotum, which indicates semen production. Generally the larger the scrotum the more semen will be produced up to a maximum of 39 cm. After that they find semen production does not increase very much. As well as the testicles, the spermatic cords and epididymis (area where the sperm mature) are also palpated for any signs of abnormality. The testicles are compared for size and shape to the opposite testicle and any differences noted including their firmness or softness. Abnormalities in any of these areas may indicate a problem, which will show up in the sperm, or may indicate bulls are producing normal sperm from only one testicle. If this is the case, servicing capacity will be markedly diminished. We want to always select bulls for higher servicing capacity.

The sperm is collected using a probe inserted in the rectum, which gives a very very low electrical impulse. This small current is increased very smoothly and causes the bull to become erect, and in most cases protrude his penis from the sheath and then ejaculate. It is important we try and get the bull to protrude the penis so it can be visualized for such things as cuts, warts or a frenulum, which is a ligamentous tie down between the penis and sheath. Most of these conditions are found on yearling bulls, albeit at a fairly low percentage. But all these conditions can render a bull infertile or subfertile. Blood, which is often present because of these conditions, is very detrimental to semen quality.

Just before inserting the probe, all the internal sexual organs are palpated for differences is size, infection, scarring and other factors. The seminal vesicles are the dominant organs, much like the prostate gland is in humans. If these become infected either from blood-borne infections or infections ascending from infected navel infections, they are all detrimental to lively sperm. Infections in these areas will show up as pus in the semen. In some cases these infections can be treated, but in the majority these bulls will be culled.

The eyes are always examined closely as ideally we want a bull with two fully functioning eyes in order to identify cows in heat. It is fairly important binocular vision exists for depth perception. Can a bull breed with one eye? Of course he can, but in a large pasture, cows in heat in the distance, could get missed.

If you as producers can eliminate these infertile or subfertile bulls by a breeding soundness evaluation, conception rates should definitely improve. Around 20 per cent of bulls can have fertility issues. It worsens in situations of large herds with multiple bulls, if the dominant bull is the infertile one. Wrecks develop in single bull pastures if a problem exists.

I have seen instances of a 100 per cent open rate, which is a situation you want to avoid. If we rank the importance of checking bull groups, the list would look something like this. Ideally it’s best to test all breeding bulls every year. If not all, at least the new young bulls should definitely be tested.

Normally as a condition of sale, the purebred breeders test all their yearlings to eliminate selling problems to their customers. Older aged bulls past their prime (beyond four to five years of age) are prime candidates for testicular degeneration and other conditions affecting their reproductive ability. Any bulls, which have been sick, injured, frostbitten or having swelling on their testicles, should most definitely be examined as well. The last group would be bulls in their prime breeding age with no previous problems. Infertile bulls can still be found in this group, but less likely.

The only breeding prerequisite that is not tested is the libido or sex drive. This we often leave up to the producer. Watching bulls breed the first one or two times in the season is always a good idea. Yearlings especially can be awkward and have a hard time entering and completing the breeding. Producers need to insure they are entering the cow and ejaculating before turning them out into the herd. Also watch for other signs during the breeding season, such as swellings on the sheath or scrotum indicating a broken or cut penis. Problems can and will happen during the breeding season necessitating replacing bulls in order to get the cows bred.

Breeding soundness exams are an integral part of any beef herd health program. Any vaccines such as footrot or pinkeye tagging might as well be done at the same time bulls are being processed to eliminate that headache in the future. Hopefully the breeding season this spring will be uneventful as far as the bulls are concerned.

Roy Lewis is a practising large animal veterinarian at the Westlock Veterinary Center, north of Edmonton, AB. His main interests are bovine reproduction and herd health.

About the author


Roy Lewis is an Alberta-based veterinarian specializing in large-animal practice. He is also a part-time technical services vet for Merck Animal Health.



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