High level of reproductive efficiency resulting in more and heavier calves is one of the most important requirements for profitability of cow-calf operations. To get a high level of reproductive efficiency, a ranch must properly manage the four Bs of beef herd fertility:

1) Body condition of cows — Cows and replacement heifers that calve in good body condition have high pregnancy rates.

2) Bugs (reproductive tract infections) — Reproductive tract infections are controlled through biosecurity and vaccination practices.

3) Balanced minerals — Balanced salt-trace minerals that contain adequate concentrations of the minerals needed for reproduction must be offered to the cattle at all times.

4) Bulls — Bulls that have passed a fertility test have higher conception and pregnancy rates.

Economics of fertility testing ranch bulls

One reason to fertility test all bulls every year is to prevent a reproductive disaster. This can happen when the bull in a single-sire breeding group of cows, or the dominant bull in a multi-sire breeding group of cows, is of low fertility.

Pregnancy rates can be below 50 percent in those situations, resulting in severe economic losses. Using only bulls that have passed a fertility test is an insurance policy against those major economic losses.

An equally important reason to fertility test bulls is to obtain increased profits through improved reproductive performance.

We have routinely observed increases in pregnancy rates when bulls are fertility tested every year on ranches served by Texas A&M University, College of Veterinary Medicine, Field Services. That would be predicted from breeding trials with bulls classified differently at their fertility test.

In single-sire breeding trials, pregnancy rates of 75 percent, 52 percent and 12 percent were found for bulls classified as satisfactory, questionable or unsatisfactory. First-service conception rates were 60 percent, 52 percent and 30 percent for the three groups.

In multiple-sire breeding groups, the impact of the benefit noted in the single-sire trials is less clear. The old idea that fertile bulls will compensate for bulls of low fertility in multiple-sire breeding pastures is false. Studies conducted on the King Ranch demonstrated five to six percent higher pregnancy rates in large numbers of cows bred by multiple bulls that had passed a fertility test compared to similar numbers of cows bred by untested bulls.

Those field trials and others have lead to the conclusion that using bulls which had passed a fertility test will improve pregnancy rates by six percent.

An estimate of the economic advantage of using bulls that had passed a fertility test can be made from data accumulated in breeding trials. We realize this is an estimate and not a guarantee. The studies were done with cattle in good condition, with proper mineral supplements and free of reproductive diseases.

There must be successful management of all four Bs of beef herd fertility to attain improvements in fertility predicted in breeding trials using bulls that have passed a fertility test.

A conservative estimate of the economic benefit of using bulls that had passed a fertility test would be to calculate a benefit:cost for the six percent increased pregnancy rate.

In a group of 100 cows bred by four bulls that had passed a fertility test there would be a predicted advantage of six more pregnancies. According to Standardized Performance Analysis (SPA), there is an average loss of six percent of the calf crop between pregnancy diagnosis and weaning in Texas. Thus, it’s likely that one of the extra pregnancies would not survive to weaning leaving five extra calves to sell.

Average weaning weight for Texas beef calves in the SPA data base for the years 1991 to 2004 is 536 pounds. At an arbitrary $1.00 per pound sale price, each of the five extra calves would be worth $536.00 for a total of $2,680.00 benefit of using bulls that had passed a fertility test to breed the 100 cows.

That is a very conservative estimate of the benefit, because in addition to getting more cows pregnant, bulls that have passed a fertility test get the cows pregnant earlier. Their calves weigh more at weaning because they are older.

Although there is little research data, some cattle reproduction specialists feel increased income from improved weaning weight could exceed the value of extra calves to sell! Therefore, a valid estimate of the financial benefit of bulls that have passed a fertility test must include the value of increased weaning weights.

A conservative estimate would be to move the mean calving date back seven days (one-third of a heat cycle). Seven days growth at two pounds per day would make each calf weigh an extra 14 pounds at weaning.

The average herd in the SPA data base had an 82 percent calf crop. In our 100-cow herd, there would be 1,148 pounds (82 calves x 14 pounds) more pounds to sell due to higher weaning weights. That would add $1,148.00 to the $2,680.00 resulting from five more calves to sell for a total benefit of $3,828.00.

The cost would be the veterinary fee for the fertility tests. Not all bulls pass a fertility examination, so five bulls may need to be examined to find four that pass. Veterinarians charge a wide range of fees to fertility test bulls. For our example we will arbitrarily use $50.00 per bull and add a $50.00 outcall fee for a total of $300.00 to fertility test the five bulls.

The breakeven cost per fertility test would be $3,828.00 divided by 5 or $765.60 per bull. Anything less than a fee of $765.60 per fertility test is increased income!  

In the 100-cow herd, using bulls that have passed a fertility test would result in increased income of $3,528.00 or approximately $35.00 for every cow in the herd. The economic benefit is actually probably greater, because fewer bulls that have passed a fertility test are needed to breed the cow herd.

It’s easy to understand fertility testing all bulls every year is one of the most profitable management practices available to beef cow-calf producers!

The fertility test

We recommend bulls be fertility tested 30 to 60 days prior to the breeding season to allow time to purchase replacements for bulls that fail. The fertility test detects bulls with abnormalities in their reproductive system. Bulls that pass are physically sound and have good semen quality. They are classified as “satisfactory potential breeders” because the test does not evaluate sex drive or mating ability. That requires observing the bull in action in the breeding pasture, a duty reserved for the bull’s owner.

It is estimated that approximately one in five untested bulls have inadequate breeding potential either due to poor semen quality or inability to service cows.

The Society for Theriogenology was formed in the early 1950s by veterinarians and animal scientists to study fertility in animals. Guidelines for evaluation of bulls for fertility were developed by the Society and most recently were updated in 1992.

There are 3 parts to the fertility test:

1) Physical examination

2) Scrotal circumference

3) Semen examination (see sidebar)

A bull must pass each of the three parts to be certified as a satisfactory potential breeder. These guidelines are minimal recommendations and individual cattlemen, especially seedstock producers, may elect to use more stringent requirements.

Physical Examination — The physical examination concentrates on parts of the bull’s body most important to fertility. The bull is observed in motion, both walking and running. Special attention is given to conformation of the hind legs and feet which during the mating act must support the full weight of the bull.

Defects such as post-leggedness or corkscrew claws are detrimental to productivity. In addition to shortening the breeding career of a bull, many conformational defects of the legs and feet are passed on to the bull’s offspring. Common heritable hind limb problems that should be avoided include post-leggedness, sickle hocks, weak pasterns, corkscrew claw and corns.

The eyes are examined to be sure that they do not have lesions that would result in significant impairment of vision. Cancer eye or scarring of either eye would impair a bull’s ability to breed.

Examination of the reproductive tract includes visualization and palpation of the sheath, penis, scrotum and testicles and palpation of the internal sex organs. Careful physical examination often detects abnormalities that would interfere with a bull’s ability to properly serve a cow or that are predictive of poor semen quality.

Scrotal Circumference – It’s important that scrotal circumference is accurately measured. Both testicles are pulled side by side into the bottom of the scrotal sac. A reading is taken from a metal scrotal tape tightened snugly around the greatest diameter of the scrotum.

The Society for Theriogenology minimal scrotal circumference recommendations for different ages are listed on page 12. These are minimum recommendations and individual breeds have their own requirements.

Scrotal circumference is related to fertility and small testicles are definitely undesirable. Bulls that just reach the Society for Theriogenology’s recommended minimal scrotal circumference for their age are just as fertile as bulls the same age that have greater scrotal circumferences.

For example, a bull with a 34-centimeter circumference at 24 months of age is generally just as fertile as a bull the same age with 38 centimeters. Both bulls have an excess of sperm producing capacity in their testicles.

A scrotal circumference of 34 centimeters or greater in all breeds and ages indicates that the testicles are adequately developed. Scrotal circumference has no relationship to libido.

There are long-term herd fertility advantages, however, to selecting young bulls with larger scrotal circumferences. Large scrotal circumference at yearling is a reflection of a highly heritable, fine-tuned hormonal system.

Age at puberty is younger in heifers sired by bulls with larger scrotal circumferences at yearling than their herd mates. Strong ­genetic correlations have been found between scrotal circumference of sire and age at first breeding, age of first calving and pregnancy rate of offspring.

Thus, selection for bulls with larger scrotal circumference should improve the future reproductive performance of the cow herd. In addition, heifers sired by bulls with larger scrotal circumferences tend to produce more milk because milk production is under hormonal control.

Semen Quality — Evaluation of semen quality involves observation of gross motility of sperm and calculation of percentage of normal sperm cells (sperm cell morphology).

Requirements for motility are lenient because motility is easily inhibited by cold or heat shock, or urine. A bull can pass a fertility test with only 30 percent progressive motile sperm cells. Percentage of normal sperm cells, however, is more highly correlated to a bull’s fertility than any other part of the fertility test. Thus, measurement of percentage of normal sperm cells is the most important single step in a fertility test.

The Society for Theriogenology guidelines require a bull to have at least 70 percent normal sperm cells to pass a fertility test. That cut-point is derived from research in the United States and Australia. An Australian study was performed over four years under extensive rangeland conditions. They performed thorough fertility evaluations including serving capacity tests with the bulls.

Calves were DNA-typed at weaning and compared to the DNA types of the bulls. Of all the measures of fertility evaluated on the bulls, percentage of normal sperm cells was correlated the most with fertility of the bulls.

The study showed bulls with 70 percent or more normal sperm cells sired higher numbers of calves, while bulls with 50 percent or less normal sperm cells sired lower numbers of calves.

To count the percentage of normal sperm cells, a slide is prepared by making a thin smear from a drop of semen mixed with a drop of dark blue eosin-nigrosin stain and classifying a hundred sperm cells as normal or abnormal under oil immersion magnification.

Study after study has found the most common reason bulls fail a fertility test is inadequate percentage of normal sperm cells. In a review of 453 fertility tests on bulls owned by a corporate farm in Texas, 105 (23 percent) bulls failed due to inadequate percentage of normal sperm cells. Those bulls would have passed their fertility test if the Texas A&M University clinicians that evaluated them had only looked at semen motility. Nearly one-fourth of the bulls would have been classified incorrectly!  

Unfortunately, too often sperm cell morphology is not done when bulls are fertility tested. This decreases the economic benefit of utilizing fertility tests, because bulls of low fertility are allowed to pass.

There is a long list of reasons the most important part of the fertility test is commonly not done. It’s not easy to calculate percentage of normal sperm cells on the ranch. Wind, rain, dust and sand often make it difficult to make a good semen smear and are hard on expensive microscopes. Some veterinarians have a policy of doing sperm cell morphology for fertility tests conducted at their clinic, but not on the ranch.

Making a semen smear and classifying 100 to 200 sperm cells takes five to 10 minutes, essentially doubling the time required to perform a fertility test. That is a problem when large numbers of bulls are fertility tested in one day. Fertility tests can be performed for a lower fee when sperm cell morphology is not done. In an effort to be low-cost producers, ranchers often elect to spend as little as possible for veterinary services. This forces veterinarians to skip sperm cell morphology to keep their charge for fertility tests low and remain competitive.

Also, some veterinarians feel that their fee for the time needed to do sperm cell morphology would make the cost of a bull fertility test prohibitive. That is not true with a very conservative estimated breakeven cost of $765.60 per fertility test.

Other veterinarians only evaluate semen motility and falsely feel that all bulls with good semen motility are of adequate fertility. Unfortunately, it’s common for bulls of low fertility to have good semen motility, because the very most detrimental defective sperm cells have good motility.

Part of the reason measure of percentage of normal sperm cells in fertility examinations is discouraged is many ranchers and veterinarians are unaware of the tremendous positive economic outcome of properly fertility testing all bulls, every year. University Beef Extension specialists and Extension veterinarians always stress the importance of doing sperm cell morphology in fertility tests, but have not empha­sized enough the huge economic benefit of using bulls with 70 percent or greater normal sperm cells.

The reasons for the profit-robbing problem of incomplete fertility tests of bulls are complex. Correction of the problem would lead to large increases in profits to cattle ranchers. Our estimates of the economic benefit of using bulls that have passed a fertility test are based on studies that used bulls that had passed a complete fertility examination according to Society for Theriogenology guidelines. A cattle rancher could not expect those levels of improvement in reproductive performance using bulls that had fertility tests that omitted percentage of normal sperm cells. Responsibility to correct the problem rests on the shoulders of us all. We are not getting the job done right!  We can do better!

Beefmaster Breeders United (BBU) is leading the way. Beefmaster bulls sold at official BBU sales are required to have passed a fertility test according to Society for Theriogenology guidelines.

Classification of bulls

The fertility test places bulls into one of three categories: