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CAREFUL BULL SELECTION CRUCIAL TO FUTURE OF COW HERD

by: Heather Smith Thomas

Careful bull selection is crucial to the future genetics of your cow herd and to the saleability of your calves. Genetics is very important in selection: EPD's for growth, milk, reasonable birthweight, etc.--all the measurable traits you want to maintain or improve on in your cow herd or calves. But just as important as looking at EPD's, sire summaries, pedigree, actual birthweight, weaning and yearling weights is examining each bull prospect visually for structural correctness or faults, and to check his breeding soundness and fertility.

Sire summaries, pedigrees and EPD's don't provide information on whether an animal is too tall, too large, too small, too thick or too narrow, nor information about structural soundness, leg conformation, muscling, testicle size, reproductive ability or longevity. The way a bull has been fed can make a difference in whether he has foot problems, adequate fertility, ambition and desire to breed. No matter how good his performance record is for growth, he won't be any good unless he can breed and settle cows. His future as a sire depends on his reproductive development and performance. His breeding abilities will affect the reproductive abilities of his offspring since fertility factors are heritable.

A prospective bull should be judged by VISUAL EXAMINATION to determine structural strengths or faults and any obvious problems that might affect breeding ability, VETERINARY EXAMINATION (semen evaluation, assessment of reproductive tract) and EVALUATION OF WILLINGNESS AND ABILITY TO BREED A COW.

VISUAL EXAMINATION -- Structural soundness should be looked at from the ground up; feet and legs are of vital importance. Bad feet, pigeon toes, long toes, straight hocks (post legged) and loose sheaths are some of the more common structural problems, according to Dr. Duane Mickelsen, Department of Veterinary Clinical Medicine and Surgery at Washington State University. Carefully inspect feet, toes, heels, pasterns, knees, hocks, sheath and testicles, and watch the bull as he moves to see if he travels well. He should move freely with some flex in knees and hocks. If he walks "funny" at all, there could be a structural problem. Each foot should strike the ground evenly, with hind feet following in the tracks of the fronts with no swinging inward or outward.

Hind leg conformation is very important; most of his weight will be on his hind legs when mating, and hind legs must be well- formed and strong. A bull with hind leg impairment may not travel enough to find cows in heat nor be able to keep up the activity necessary to court and breed a large number of cows. Some bulls with hind leg problems will mount cows but not breed them, due to rear leg discomfort, says Dr. Mickelsen. To be athletic, to travel well and be able to service cows, a bull should have proper angles in feet and legs. If hind legs are too straight (post-legged) or too angled (sickle hocks) the bull may be susceptible to injury.

If a bull is too straight in the shoulder and pasterns, and too straight in the hind legs (post-legged) he will have problems. This type of bull often has a short, choppy stride, carries his weight on his toes, and may have small feet, says Mickelsen. This type of conformation may make his front legs buckle at the knee. The post-legged bull often suffers stifle injury or hock problems. Post-legged cattle are often tall, but this is poor conformation.

Too much angle in the hind leg (sickle hocks) puts too much weight on the heels; heels are often shallow and toes grow long because they don't wear normally. The ideal foot has a strong, deep heel and well formed hoofs. If one toe is obviously wider or longer than the other, there is probably uneven weight distribution caused by conformational faults further up the leg, says Mickelsen, resulting in uneven wear and abnormal hoof growth. In most of these cases, foot trimming is needed because of poor conformation.

As a bull with poor hind leg conformation ages, the problem becomes more apparent and tends to increasingly interfere with breeding ability. This type of bull is a poor risk because he not only sires fewer calves, but his structural faults are likely to be passed on to his offspring.

Other feet and leg problems (apart from inherited conformation faults) can stem from overfeeding when a bull is young and growing, says Mickelsen. "Bulls that have been pushed to gain four to five pounds a day are at risk of founder. And if a bull is overfed you should really question his breedability." An overfat young bull has too much stress on his immature skeleton; growing bones and joints can be permanently damaged by the extra weight. "If a bull on hot rations goes off feed even just a little (acidosis -- indigestion caused from too much grain in the diet) he may founder, and have later foot problems. He won't be able to travel," says Mickelsen.

When evaluating a bull, look at his overall condition. A bull too thin may not be able to handle the stress of breeding season, and a bull too fat won't have the athletic ability and stamina to breed a lot of cows; he'll be sluggish and tire easily, warns Mickelsen. Young bulls that have just completed weight gain performance testing are usually too fat, which interferes with their performance as breeders and can also hinder fertility -- since fat in the testicles provides too much insulation for proper temperature necessary for sperm production and viability. Overfat young bulls may also lose weight too rapidly their first breeding season. To avoid these problems, an over-fat young bull must be allowed at least two months "let down" period on a high roughage diet before being used for breeding, and even then some of them will not do well at pasture breeding cows, says Mickelsen.

SCROTAL SHAPE AND CIRCUMFERENCE -- Scrotal size and shape are good indicators of fertility. Shape is important, since a bull has to be able to raise and lower his testicles for proper temperature control. The testicles should hang down well away from the body in warm weather. There should be an obvious neck at the top of the scrotum with the testicles hanging down large and pear-shaped. A bull with a straight-sided scrotum or a "V" shaped scrotum is often not as fertile as a bull with a normal scrotum, says Dr. Mickelsen.

Don't choose a bull with odd-shaped testicles (one obviously smaller than the other) and note any abnormalities. "Scabby, thickened skin, especially on the back or bottom third may indicate frostbite, which can cause temporary or permanent infertility, depending on the extent of damage and scarring," says Mickelsen.

Testicle size is an excellent indicator of fertility since a significant correlation exists between scrotal circumference and sperm cell volume and percent of normal sperm cells. There is also a strong genetic correlation between scrotal size in bulls and the fertility (as measured by age of puberty) of their daughters. Bulls measured at one year of age should have scrotal circumference of at least 32 centimeters, preferably 34 to 36. For best fertility, and to insure high fertility in a bull's offspring, select bulls with above average scrotal circumference.

Bulls with small testes not only have lower sperm production but often suffer from other problems that make them subfertile or infertile, says Mickelsen. Infertility associated with small testicles may result from incomplete development or under- development of these organs and/or testicular degeneration, he says. Some bulls with scrotal circumference of 29 centimeters or less may produce no sperm at all. Bulls with smaller than average testicles may be fertile at first, then eventually become less fertile or completely sterile because the tubules within the testicles degenerate earlier and at a more rapid rate than in a normal bull. Also there is more abnormal sperm in the semen of bulls with small testes, probably because of early testicular degeneration, says Mickelsen. Keep in mind that all types of testicular underdevelopment are heritable.

VETERINARY EXAMINATION -- A semen check and physical examination of the bull's reproductive tract by a veterinarian will also help you tell if a bull will be a satisfactory breeder. The vet will check for adhesions caused by injury or bruising in the sheath or penis, and any abnormalities that might interfere with breeding. He will also examine and palpate the scrotum, testes and epididymides. Some bulls may have one testicle only partially descended into the scrotum, and some may have scrotal hernias. Normal testes and epididymides are usually symnetrical, says Mickelsen, so any deviation in size, shape or relative position should be viewed with suspicion. The vet will also check for tumors, and enlargements due to inflammation and abscesses.

A semen check will indicate whether the bull has adequate numbers of live sperm and whether he has a high or low percentage of abnormal sperm. If a bull has a high prevalance of a specific sperm abnormality, he is usually infertile, says Mickelsen. A high number of sperm with abnormalities may mean the bull is sexually immature or that there are degenerative changes in the testes. Abnormal sperm usually decrease as the young bull matures or his testes become larger. A bull that does not show normal sperm evaluation by 16 to 18 months of age is a poor risk as a breeder.

Jim White, who runs the Northwest Bull Test at Parma, Idaho, says there can be a lot of change in a bull between 12 months and 16 months of age. "Some of these bulls won't pass the test as yearlings--they are too immature. Out of 100 bulls there will be about 10 that don't check out, and some of those have a problem, such as small testicles or a soft testicle, but some bulls just need to be rechecked in a few months. Many will be ok in their sperm production by then." He also says you should not rely on just a semen check. Conditions can vary (bad weather, cold or hot weather, or other stresses) which can temporarily affect a bull's test score.

Mickelsen says one factor that can cause temporary increase in sperm abnormality (and resulting decrease in fertility) is heat stress. About two weeks after experiencing heat stress, abnormal sperm will appear in the semen and continue to increase for up to a month later. After that, the sperm will become more normal again, unless the heat stress continued for a period of time, in which recovery will take longer. Heat stress in July through early August may make a bull infertile through September, reaching full recovery as late as December. Fever can do the same thing, as when a bull suffers from illness or foot rot; he will have a period of infertility following the time when sperm production was adversely affected by the fever.

LIBIDO AND MATING ABILITY - Structural soundness and high quality semen are not enough to classify a bull as a satisfactory breeder if he cannot mount and service a cow. Libido, or sex drive, is a vital part of fertility and has little relationship with other traits such as semen quality. Libido is defined as the willingness and eagerness to mount and service a cow; mating ability is defined as ability to complete the service. Deficiencies in either can seriously limit a bull's ability to sire calves.

Libido is an important aspect of a bull's breeding ability, but is difficult to evaluate during a breeding soundness exam. The bull must be observed with cows. Young bulls must learn to identify cows in heat. It's always a good idea to expose young bulls to a few cycling cows before the breeding season, to evaluate their breeding ability. Shy breeders, fighters (prefering to fight other bulls rather than breed the cows), bulls that stay with one cow and ignore others in heat, and bulls with poor sex drive or poor mounting ability will not sire very many calves.

Strong sex drive or lack of it often has a genetic basis, but other factors may be involved, says Mickelsen. Some bulls raised in all male groups may show temporary low libido, as will bulls that have been overfed. Bulls in poor condition, or suffering from disease, pain, stress (handling or environmental) will also show decreased libido. Mating ability can be impaired by lameness, rear leg unsoundness, or back problems. Penile abnormalities and injuries can reduce mating ability, and if there is more than one bull in a breeding pasture, social dominance can also be a factor.

A breeding soundness exam gives a good clue to a bull's potential, but the only true test of his breeding ability is in the breeding pasture -- where cows are bred and settled. A careful evaluation of the bull beforehand, however, can often help you avoid choosing a bull with problems that may interfere with his future as a sire.

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