Bull Management in Preparation for the Breeding Season


Once calving season rolls around, there is nothing more devastating and heartbreaking than loosing a newborn calf, either during calving or immediately after.  Although not nearly as dramatic, a reduction in the number of calves conceived and born due to infertility or injury in your herd sire is likely to impact your operation on a much larger scale and is generally far more important in the overall scheme of things.

 We like to assume that the bull is always out there doing his job, but there can be a number of factors that limit or destroy his ability to successfully impregnate his cows.

He must be physically sound, he must be fertile and he must have adequate libido.  Without saying, he must also be exposed to cows that are capable of becoming pregnant, but that is another subject.

 Cow/calf management experts, without exception, highly recommend a breeding soundness exam every year on all bulls used for natural breeding.  Ideally this is done 30-60 days prior to turnout with the cows.  Obviously, the longer the time period between the examination and the start of the breeding season, the less accurate favorable results become.  Bulls can be examined anytime relative to the breeding season, and there may be advantages to testing at a different time.  Examination immediately following the breeding season can give the manager a heads-up on possible problems in the past breeding season, as well as allow plenty of time to find a replacement bull.  Examination at weaning time has the same advantage in finding a new herd sire, where springtime testing, the most accurate in relation to the upcoming breeding season, may not allow enough time to locate the quality bull you may require as a replacement if that becomes necessary.

 A bull has to be physically sound in order to be a reliable breeder.  He needs to be able to see, eat, smell and move around on sound legs and feet in order to successfully breed his cows or his share of cows.  A history of recent illness is also important, as that may temporarily (or permanently) impair his fertility. 

 Eyesight is important as he must be able to spot heat activity from a distance.  A bull uses his eyes to see any riding that might be taking place among the cows.  A bull with poor vision, or blind in one eye is dangerous to handle and is more likely to injure his cows.  If he is part of a multiple bull pasture, he may be intimidated by other bulls so that he will not even attempt to breed cows.

 The bull requires enough body condition to be strong with some energy reserves in the form of fat.  Body condition scores should generally be in the 5 to 6 range.  This requirement will vary depending on range conditions, time of year and number of cows to service.  Overly fat bulls have decreased fertility and decreased stamina for seeking out and mounting cows in heat. Feeding high energy diets to young bulls may damage their sperm producing ability.  This is usually seen in bulls fed concentrate between 60-70% of their total ration; and they will resemble a steer ready for slaughter rather than a well-grown potential herd sire ready to work.  The poor quality sperm produced in this situation is likely due to the poor thermoregulation in the scrotum caused by too much fat.  Certainly the stress associated with groups of young bulls on heavy feed as seen in some bull tests may also contribute to poor quality semen.  This is generally a correctable problem; once the bulls loose weight, the fat insulating their testicles will decrease and sperm production can return to acceptable levels.  Weight loss in these animals may actually result in a smaller scrotal circumference than that measured while still on feed due to the large volumes of fat that can surround the testicles.

Feet and legs need to be structurally correct.   Most structural flaws are heritable and many can lead to lameness under hard and heavy use.  A bull traveling over rough, hard ground will have relatively even wear on each hoof and will seldom have foot problems if he is structurally correct.   Needless to say, correctible forms of lameness such as interdigital corns, footrot or puncture wounds, should be treated and cleared up prior to pasture release.  Long hooves should be trimmed at least 4 weeks prior to turnout.

 Once it has been determined that your bull is physically adequate to use for breeding, a thorough evaluation of his reproductive organs and semen is warranted.  This examination should be performed by someone with significant experience in fertility evaluation in bulls, whether a veterinarian or a competent, experienced AI technician.

 The internal organs can be examined by rectal palpation.  The vesicular glands, ampullae and prostate all need to be palpated for evidence of inflammation, adhesions or fibrosis (scarring).  The external reproductive organs also need to be examined for changes suggestive of abscesses, injury, frostbite or tumors.    .

 The penis and sheath should be examined at this time; with attention paid to signs of sores, lacerations, abscesses, scar tissue, hair rings, warts or adhesions.   Hair rings around the penis are reasonable common, particularly in yearling bulls and may actually be more of a risk in Highlands because of the long hair.  If undetected, a simple little noose of hair wrapped around the shaft of the penis, can turn into a nightmare.  As the bull grows, the penis grows while the hair ring stays the same diameter and may actually cut into or strangulate the end of the penis.   If the tip of the penis is destroyed, this may ruin the bull for natural service; as the tip of the penis actually helps the bull to locate the vaginal opening of the cow he is breeding by sensing the temperature change.  An early hair ring is usually very easy to remove during a routine breeding soundness exam.

Old lacerations and adhesions may prevent the penis from completely extending, or cause pain.  Warts on the tip of the penis are fairly common also, and need to be removed. Bulls with any painful condition will typically lose their desire to breed cows.

 The testicles are the locations where the sperm is actually produced, and they should be firm, equal in size and adequate to large for the bull’s age. The shape of the scrotum is an important factor also.  Normally, the scrotum will appear as a full sack dangling on a thinner neck. The testicles require a temperature a few degrees below body temperature to produce live sperm, thus they are suspended away from the heat of the abdomen.  A straight sided scrotum (no appearance of a thinner neck) is often associated with only moderate sized testicles and is usually caused by excess fat deposition.  This can easily interfere with normal spermatogenesis due to faulty thermoregulation in the scrotum.  As bulls mature and/or lose fat, often the scrotum will become more normal in appearance.  A wedge-shaped scrotum is pointed toward the bottom and tends to hold the testicles closer to the body wall.  Bulls with wedge-shaped scrotums tend to have undersized testicles that are subfertile, and should be culled.  The scrotum also needs to be examined for evidence of frostbite which can cause significant injury to the testicles.

 Scrotal circumference is a very important measurement because it correlates well with daily sperm production.  Bulls with bigger testicles usually produce more semen, and sire sons with bigger testicles.  Bulls with larger testicles also tend to reach puberty at a younger age and sire earlier maturing heifer. Obviously, the more semen that a bull produces, the greater the number of females he can settle. Bulls must meet a minimum scrotal circumference based on age in order to pass a breeding soundness exam. Although there is some variability in scrotal measurements based on breed, reproduction experts agree that these minimums should be met by all breeds of bulls, even those that have been documented with slower maturation.  Incidentally, Highlands are not one of the breeds considered to be “slow maturing.” This terminology generally refers to the age that they will hit puberty, and Highland cattle seem to be right in the ballpark in this trait.

Once it has been determined that your bull has normal reproductive organs the next step is to collect a semen sample.  Bull studs may use a cow in heat and an artificial vagina for semen collection, but the vast majority of semen evaluations conducted in the field are collected using electro-ejaculation.  The quality of semen collected this way is excellent to determine fertility, but there will be some instances where it is impossible to collect a particular bull using this method.  Failure to get an adequate sample for evaluation after a single attempt does not automatically mean the bull is not fertile.

 Electro-ejaculation involves the insertion of a rectal probe that stimulates the prostate gland via electrical currents, leading to erection and then ejaculation.  While the procedure sounds barbaric, the level of electrical current is minimal, and it should not be a painful experience.  Bulls inexperienced with the procedure may vocalize a fair amount during collection.  Bulls used to the procedure do not seem to mind at all, and in fact, some will act as if they look forward to it.

 Once the semen is collected it is evaluated for a number of characteristics.  Motility of the individual sperm cells is very important to fertility.  If the sperm can’t swim, they can’t make it to the egg to fertilize it.  Ideally, the sample would have over 90% vigorous, progressively motile sperm cells, but this motility must be evaluated on a warm semen sample.  Cold shock can decrease motility dramatically.  Special heated equipment allows for the examination of sperm without losing significant amounts of natural motility. Less than 30% motility places the bull as an unsatisfactory breeder.

 Morphology, or the shape of the sperm cells, is also a very important part of the semen evaluation.  A small sample of semen is placed on a microscope slide, stained with special stains, and then at least 100 sperm cells are graded for normal shape.  Sperm cells with droplets, bent or coiled tails, malformed heads or other defects, are less apt to successfully fertilize the egg.  Abnormal cells should be less than 25% of the total number counted in ideal circumstances.  Anything more than 30% abnormal cells would warrant failing the semen evaluation.  Morphology also includes evaluation of the sample for the presence of blood or inflammatory cells, which could indicate potential fertility problems.

 After the breeding soundness exam is complete, the bull will classified as a satisfactory potential breeder (passing scrotal circumference, motility and morphology with at least the minimum standards,) or an unsatisfactory potential breeder (failing to meet just one of the minimum requirements).  If there are circumstances which would indicate this bull might be immature or have a treatable condition such as a balanoposthitis (inflammation of the prepuce and glans of the penis), bloody semen as a result of a wart or hair ring, or others, his classification may be deferred to a later time.  It is not uncommon for immature bulls 11 – 13 months old to have poor quality semen that would classify them as unsatisfactory breeders.  In the case of these young bulls, semen quality has been shown to improve for about 16 weeks following puberty.  Therefore, should one of these bulls fail a semen evaluation, he can be reexamined when he is about 16 months old and there is a good possibility that he will prove to produce adequate semen quality. Bear in mind though, that this only has to do with the quality of the semen and has no bearing on scrotal circumference measurements.  The minimums for scrotal circumference are etched in stone; those testicles need to be at least a minimum size for adequate fertility in acceptable numbers of cows. 

 Libido is probably the hardest of all the breeding qualities to measure and is also very necessary for a bull to settle large numbers of cows.  Some bulls will be intimidated by the presence of another bull, or even a group of cows trailing after one of their own in heat. Unfortunately, sex drive and semen production do not appear to have any relationship.  Excellent semen can be collected from low libido bulls and extremely aggressive breeders may be completely sterile.  There are standardized tests for libido utilizing heifers in standing heat, but they are cost prohibitive, as well as impractical in most field situations. 

 So what do you do if your bull fails his breeding soundness exam because of his semen quality or scrotal circumference?  That answer depends on a couple of factors.  Again, if he is an 11-13 month old bull, repeating the semen evaluation every 3-4 weeks may show that he is in fact quite acceptable. 

 Minimum Recommended Scrotal Circumference for Age

   12 to  <  15 months     30 cm

> 15 to <  18 months      31 cm

> 18 to <  21 months      32 cm

> 21 to <  24 months      33 cm

      > 24 months             34cm

It is common for yearling bulls, owing to immaturity, to require a second fertility examination to achieve satisfactory potential breeder status. There are no recommended values for bulls less than 12 months old.

There is no standard scrotal circumference for bulls younger than 12 months.  Roughly speaking, bulls receiving good nutrition will increase scrotal circumference by over 1 cm per month.  A bull reaching 29 cm by 11months will probably pass by the time he is 12 months old.  Likewise, a bull reaching 29 cm by 13 months still has 2 months to reach the minimum standard if he is retested.  However, a bull measuring 29 cm two days before his 15 month birthday, has to not only increase to 30 cm before he turns 16 months old  (in about 30 days)  he also still has to reach 31 cm by the time he turns 16 months old in 32 days. In all likelihood, he can’t make it. Remember also that in terms of fertility, the greater the scrotal circumference, the more sperm that bull should be able to produce. Small testicles at 12-15 months almost always translate into small testicles as a mature bull.  In this particular case, bigger is always better. All other things being equal, take the bull with the larger testicles.

 If the bull’s semen quality is adequate, but his scrotal circumference does not meet the minimum, he can probably settle a small to medium number of cows, but he absolutely should not be turned out with large numbers of cows to breed. His sperm producing capability is limited: he will not be adequate to breed large numbers of cows.  Furthermore, his sons may well end up with small testicles and reduced fertility.  His daughters too may be affected with delayed puberty. You should think seriously whether you want to use him.

 If your bull has large numbers of abnormal sperm causing him to fail his semen exam, he could be carefully monitored with a few select cows, remembering that if one of those abnormal sperm fertilizes that single egg, the cow will no doubt abort the embryo, and she won’t  produce another egg for 3 more weeks. You have very good odds of wasting one or all of her heat cycles. This bull should be retired unless you can justify the very real and very high risk of open cows at the end of the breeding season.  

 If your bull has large amounts of inflammatory cells or blood causing his classification to be deferred to a later time, your options are to replace him immediately, or determine the cause of the problem and treat it, hopefully successfully.  Causes of inflammatory cells can include something as simple as balanoposthitis.  This can be caused by the hair around the prepuce getting tangled with matts or burrs, leading to retention of slight amounts of urine being retained around the opening of the prepuce and the glans of the penis.  This leads to irritation and inflammation that is easily corrected by trimming the offending hair, so that urine is no longer retained.  Sometimes antibiotics would be warranted.  Penile warts are usually easy to remove, although they may return.  Other more serious causes of inflammation may not respond to treatment however.

 If the bull has no sperm and is officially sterile, he can’t be used.  He also can’t be put with the cows and another, fertile bull; just to “keep the old guy around”.  He will not know that he is sterile, and will attempt to breed as many cows as possible, keeping a fertile, but less aggressive or intimidated bull from completing the task. This bull no longer is any use to you.  If you want to keep him as a pet, give him a pregnant cow or a steer, or even your young bulls that you aren’t using as companions.  If you can’t do that, he needs to go.

 Hopefully, by having a breeding soundness exam done on your herd sire, you will rest easy in knowing that your new purchase was a good investment, or your old favorite is still capable of doing his job.  If the results are less than what you hoped, you will have the opportunity to make some very important, and very informed, decisions concerning the management of your herd.


A Word on Growing Young Bulls

 Cattle eat somewhere between 1-3% of their body weight per day in dry matter.  Paradoxically, those animals consuming the lower amounts of feed per day are actually those eating the poorer quality feed because the rumen can only process extremely high fiber diets at a reduced rate of speed.  Extremely digestible, high quality diets are processed much faster, thus emptying the rumen and making room for more feed at a more rapid rate.  So a 1000# bull fed 10# of grain and 20# of high quality alfalfa hay is getting less than 1%   of his body weight in grain and about 30% of his total feed as high energy feed. This is actually a pretty good growth formula without promoting fat.

 A 1000# bull fed 20# of concentrate or more, along with 10# of hay, is now getting almost 2% of his body weight in high energy feed and about 60% of his total ration in grain.  This is a very high energy diet that should be considered a fattening, or finishing diet, rather than a growth diet.  This diet can easily be associated with subclinical acidosis, laminitis (founder) and numerous digestive upsets.  Bulls grown out on this type of diet need a readjustment period to allow their digestive system to “relearn” how to process high fiber (pasture).  Bulls consuming this type of diet will loose tremendous amounts of weight if they are taken off this ration cold-turkey. It is possible that some bulls in this category may never make the transition. (This applies to females fed in this manner also.)









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