01/17/2022
Don wrote this shortly after we graduated from vet school. Not much has changed, but we would always recommend rechecking yearling bulls even if they are semen tested prior to purchase. We flunk several yearling bulls every year that have already been tested. We have tested some bulls who were found satisfactory on a BSE prior to sale and found persistent frenulums.
Bull advertisements jump out of every page of the classifieds this time of year. ‘Tis the season to shop for your herd’s next bull(s). As you shop, bear in mind a few points to ensure your expensive purchase maximizes cow herd fertility. This discusses the importance of health and the value of performing a breeding soundness exam (BSE) on bulls.
The producer can detect potential problems with a bull prior to purchase. Too often the most emphasis in selecting a bull revolves around his expected progeny differences (EPDs). EPDs are important but other physical traits can be the downfall of a genetically superior bull. Close attention should be paid to the bull’s toes. Long toes, scissor toes, corkscrew claws and cracks in the hoof wall may lead to lameness. Bulls with toe problems may never become lame but are higher maintenance needing hoof trims every 6-12 months to prevent lameness or poor locomotion. Bulls with a posty (upright) stance or those that stand low in the heels are more likely to become lame. Contrary to common perception, vision, not smell, is the sense a bull uses to detect cows in heat. Therefore bulls with bad eyes are poor candidates for purchase. Producers should select against bulls with a weak preputial muscle. As a result of this weak muscle, the prepuce hangs out allowing for injury by environmental factors (vegetation, drying, etc). This injury could lead to infection and scarring preventing the bull from retracting his p***s, leading to further injury/damage. Focus on physical traits when purchasing your next bull is the first step to maximizing cow herd fertility.
Next, the philosophy for performing a BSE should be discussed. The ultimate goal of a commercial beef cattle herd is to produce the most pounds of beef per exposed cow. The best way to accomplish this is to get the cows bred in a short time period. Calves born one cycle later (21 days) are at a 50-60 pound weaning disadvantage compared to a calf born a cycle earlier. Therefore, a subfertile bull could result in a significant economic loss when he does not get cows bred in a timely fashion. Thus, it pays to have a highly fertile bull. A BSE must be performed to detect a highly fertile bull.
A highly fertile bull has the best chance of fertilizing a cow’s egg on his very first service. Studies have been performed to show that bull’s s***m needs at least a fair to good motility (>40 percent motile s***m) and greater than 70 percent normal s***m morphology to achieve high fertility. Nationwide only 70-80 percent of bulls achieve a satisfactory rating (= highly fertile) on a BSE. Bulls fail due to poor s***m, poor feet, immaturity, and or poor health. By 16 months of age nearly 100 percent of bulls have reached s*xual maturity. However, because of s*xual immaturity 26 percent pass the BSE at 12 months and 53 percent pass at 14 months. So, a BSE after 16 months of age is a better indicator of his fertility potential.
The veterinarian looks at all the previously mentioned physical traits and examines the p***s, sc***um, testicles and other reproductive organs (seminal vesicles) during the BSE. In addition to visual and palpable examination of these structures the veterinarian will collect semen for microscopic evaluation. The p***s is observed for persistent frenulum, hair rings, and warts after extension with the electroejaculator. Persistent frenulum is rare genetic problem encountered in yearling bulls that must not be missed. Since this is a genetic condition, progeny should not be reserved for replacements. Hair rings should be removed for they may result in a stricture. Warts occur on the shaft or tip of the p***s and are surgically removed if possible. Warts can be effectively prevented with a commercial vaccine. Corkscrew and deviated p***s problems must be evaluated during natural service since some bulls may falsely show a corkscrew p***s with electrical stimulation. Scrotal circumference is another parameter measured during the BSE. Circumference is directly related to the weight of s***m producing cells. 12 month old bulls must have a measurement/circumference greater than 30 cm to pass. Daughters of bulls with smaller scrotal circumferences reach s*xual maturity later than daughters of bulls with large scrotal circumferences. Palpation of the seminal vesicles rectally can detect swollen, firm, lobulated or otherwise abnormal vesicles. The cause of enlarged and painful vesicles is commonly infection of viral or bacterial origin. Treatment with high frequent doses of Micotil can resolve the problem in yearlings but older bulls do not respond to treatment therefore they should be culled. Infected vesicles produce pus which introduced to semen kills s***m. Semen is collected using an electroejaculator but does not affect the s***m. The electric current causes contraction of the smooth muscles resulting in ej*******on. Immediately after collection, motility (percent of forward swimming s***m) is observed microscopically. It is often classified as poor, fair, good, or very good. Fair to good is required to pass. Next, the semen is stained and 100 s***m cells are counted. The cells are categorized as normal or abnormal. The count gives a percentage of cells in each category. A 70 percent normal s***m count is needed to pass the BSE. Problems with s***m can arise from genetics, injury etc. Heat injury to testicles results from frostbite (inflamed testicles that are held too close to the body) hot weather, infection, etc. Temporary testicular problems resolve in 60 days. Stressful events (extreme weather, storms, lameness, illness etc.) can cause defects originating in the epidydimis. Temporary epidydimal problems resolve in about 2 weeks. Permanent damage to these structures will continue poor results indefinitely. These are the most common parameters evaluated and problems detected by a veterinarian performing a BSE.
Another factor in bull fertility not easily measured is libido. Libido is the bull’s s*x drive. Libido is measured by turning a bull out on a tied up cow that is in heat. The number of mounts in a specified period of time is used to classify the bull. This is obviously difficult and expensive to perform. 10 -20 percent of bulls that pass a BSE will have low libido which also results in an extended calving season. Passing a BSE has no correlation to a bull’s libido so this is up to the owner to observe. A side note concerning multiple sire pastures follows; 80 percent of cows (in a multiple sire pasture) will be served by 2 bulls with normal libido. 50 percent of cows will be served by 3 or more bulls in a multiple sire pasture.
Many observations are collected during a BSE. All are relevant to the bull’s passing his BSE. Some can be detected by the producer, others require detection by a veterinarian. To ensure a successful breeding season and profitability, the bull must pass all parameters. With strict attention to detail phenomenal results can be achieved. A herd of cows in Canada consistently has an 85 percent pregnancy rate in a 25 day breeding season. This is due to highly fertile bulls and cows with a good body condition score.
To succeed in today’s beef industry a producer must get the most efficiency out of each dollar spent. A subfertile bull can really eat into a producer’s pocketbook. BSE’s are a great tool to help choose the most fertile bull.