Judging business-end of bull, 2014

The business-end of the bull

„When I buy a bull, I always start by looking at the back end of the bull. That’s where the business end is. I want to see large testicles and a well-shaped scrotum. That’s the most important part of a bull. No matter how good he is otherwise, if he can’t sire calves, he’s no good to me. It doesn’t matter if he is the best walking bull in the world, if he hasn’t got the equipment to do the job he’s no good.”

(Wise US beef producer)

This chapter is mainly intended for herds with natural mating. To mate a large number of females successfully a bull must be structurally correct, well adapted to his environment, have libido or sex drive and must have the correct reproductive anatomy of which scrotum is extremely important. Without these features a bull with the best genetics is useless.

The US Society of Theriogenology breeding ability system has become the standard by which bulls are measured for breeding soundness. Scrotal circumference (SC) is so important in this system that it represents 40 % of the total score (others are semen

morphology 40 % and semen motility 20 % as well as a physical examination). Scrotal size

Scrotum volume or weight plays an important role in the fertility of the bull and his daughters. Since this volume/weight is an impractical measurement we measure the SC instead. Numerous studies in many countries with all beef breeds showed the following advantages in selecting bulls with a larger SC:

(I) Improves the bull’s semen volume and quality;

( II ) Earlier puberty of the bull;

(III) Earlier puberty of the bulls daughters;

(IV) Greater life time reproductive potential of daughters.

In the 1980’s I did some research on this and subsequently we decided to make SC a mandatory component for registration by introducing minimum SC standards for herdbook entry as well as shows. Measuring sticks were available at every show in case the judge queried the SC of a bull.

Because the scrotum plays such an important role judges must be familiar with this topic and create awareness of these matters when bull classes are explained to the audience. Rate it high in your judging value assessment and encourage the recording of SC amongst breeders.

„I am surprised that many judges don’t even mention scrotum matters at shows. After all fertility is much more important than growth rate, size and muscling.”

(Author)

The function of the scrotum is to cover, support and protect the testicles and to maintain a lower than abdominal temperature. Sperm production occurs at a temperature of 4 to 6° C below normal body temperature. A temperature sensitive layer of muscle in the wall of the scrotum relaxes when hot, thus moving the testicles away from body heat and contracting it when cold which shortens the scrotum and the testicles are held

Chapter 21

close to the warm body. Bulls that get high growth rate rations, usually deposit fat in the scrotum which interferes with this temperature control.

Scrotum issues breeders and judges have to be familiar with

It is advisable that judges make use of the following

© P Massmann

when bull classes are discussed:

° SC is highly heritable (around 0.45) and selection for positive SC EBVs (1) should improve the fertility traits (I) to (IV) above.

° Judges should point out to the audience that SC EBV has a high correlation with with yearling weight and a low correlation with birth weight which suggest that selection for larger SC EBV’s should result in increased growth from birth

to yearling while holding birth weights relatively constant; an ideal situation.

° SC is an easy and accurate measurement. Use a flexible tape or even better a SC „loop ­ stick“ slipped over the widest point of the scrotal sac with the testes fully descended. Watch out for a scrotum which is not fully descended (normally in cold weather) because it may have wrinkles on the scrotum that will inflate the measurement.

Minimum scrotal size

I am not sure how many SF associations around the world have minimum SC standards for registration but here are a few guidelines.

° In Africa SF bulls must meet the following minimum SC size for registration and for shows:

<400 kg = 32 cm, 400 ­ 450 kg = 33 cm,

450 ­ 500 kg = 34 cm, 500 ­ 550 kg = 35 cm, 550 ­ 600 cm = 36 cm and >600 kg = 37 cm.

(1) = Since the EBV reflects relative genetic merit without the influence of an environment (for example feeding) it is a much better selection tool in comparing bulls than the raw SC measurement. The SC EBV can be compared across herds and environment.

 Figure 21.1: The business end of the bull. Scrotum circumference is an easy and accurate measurement to obtain fertility breeding values. Measuring devices like here should be available at all shows. Here a well-developed (large) scrotum with symmetrical testes and scrotal neck without fat deposits.

 Figure 21.2: Left and middle, fat deposits in the scrotum neck like here lead to lower fertility or temporary sterility. Right, scrotum too long and will be susceptible to scrotum injuries under extensive conditions.

© P Massmann

° Coulter recommends these minimum SC for SF:

12­14 months = 33 cm; 15 ­20 months = 35; 21­ 30 months = 36 and >30 months = 37.

Is bigger better?

Scrotal development is curvilinear (goes up fast and then flattens out) and increases from 2 to 3 centimetres in Bos Taurus from around 6 months to 2 years when it will reach about 90 % of it’s mature

size (Coulter). Judges should not propagate „the biggest is the best.” I did not come across a study comparing large SC with long hanging scrotums but my research amongst buyers of bulls with very large yearling SC (measured at central performance test centres) revealed that when older, these bulls have increased incidences of scrotum injury under extensive ranching conditions in bushy areas because of long scrotums and the scrotum also bumps against the legs when walking long distances. A Canadian vet reports that SC above 38 cm at yearling does not result any more

semen production and that „invariable problems are encountered with abnormally large scrotal size”.

Scrotal shape

Normal testicles are symmetrical with a distinct neck without fat deposit and freely movable in the scrotum. I recommend that judges in countries where natural mating is common to disqualify bulls with the following abnormalities:

The straight-sided scrotum (left Figure 21.4) lacks size and I found a few references that these bulls are not as

fertile as bulls with a normal scrotum. The straight­ sided neck of the scrotum is generally the result of fat deposits that may impair proper thermoregulation.

Wedge-shaped scrotums are pointed toward the bottom and hold the testicles close to the body wall. Bulls with this scrotal make ­ up have undersized testicles and seldom produce semen of adequate quality.

It’s disturbing that so many SF judges don’t give enough emphasis to testicular hypoplasia, a deformity where one or both testes are underdeveloped. In a

 Figure 21.3: Symmetrical testicles, scrotum neck without excessive fat deposit and ideal size. © J Lueese

 Figure 21.4: Scrotal shape abnormalities f.l.t.r.: Straight sided, Pear-shaped and commencement of one-sided hypoplasia. © P Massmann; Drayson

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one ­ sided hypoplasia the effected testis is about 1/ 3 to ½ the size of the other one. This condition is not the same than testicular cryptorchidism were one testicle remains in the abdomen instead of descending into the scrotum. Both these abnormalities are heritable. The effect of a twisted scrotum on the fertility of a bull has led to much discussion among judges over the years. P v Rooyen in S. Africa measured many scrotums of fifteen breeds with a „twist­ meter“ and found that around 50 % of the bulls showed scrotal twist, of which 87 % twisted to the left. He is of the opinion that scrotal twisting has no effect on the normal functioning of the testicles and warns that this condition should not be confused with testicular torsion where the testicles twist inside the scrotum which has a detrimental effect on the functioning of the testes. The US Society for Theriogenology point out that testes may rotate up to 40 degrees.

Sheath and prepuce

Although prolapse of the prepuce is a problem among Zebu and Zebu influenced breeds and not a concern with SF, many studies with Continental and British breeds show that prolapse problems are much more prevalent in polled bulls than horned bulls. The sheath should be attached close up against the body at a less than 45°angle from the horizontal. A long, pendulous V­ shaped sheath (more than 45°) is prone to injury or infection from bushes and grass seeds and should be avoided. The same applies to prolapse of the prepuce (the lining of the sheath) which causes the exposed tissue to become damaged. A bull which lets the prepuce hang out for long periods should be regarded as having a structural fault we don’t want in the SF breed.

Summarize undesired

• Small scrotum – less than the above mentioned measurements;

• Abnormal shape: Wedge, straight and twisted more than ±45°;

• Too long – hanging below the hocks;

• Cryptorchidism where one or both testes are undescended;

• Long sheath, large sheath and a V­ angled sheath;

• Large sheath opening, prolapse of the prepuce.

„Traits associated with reproduction have about five times more economic value to commercial beef cattle production than do those associated with calf growth or production of the milk by the cow”.

(Trenkle and Willham)