by: Stephen B. Blezinger
Ph.D., PAS

About this time every year thousands of cattle operations are hip deep in calving so attention is given to this important event. And while this is obviously extremely important for the producer and insures a paycheck in the fall, at this same time it is important the proper ground work be laid for the NEXT calf crop, the one we will calve next winter/spring.

One of the most important steps the producer can take at this time of the year, for his spring calving cow herd, is to insure that his bulls are properly prepared for the breeding process. Many producers have run into the situation where they have turned the bulls out and anticipated that the result will be a pasture full of pregnant cows only to discover several months down the road that they had a collection of open cows or at least way more than they would have liked. The reason being that the bull or bulls they were using was not fertile, structurally sound or any number of other problems.

This article will take a moment to discuss getting bulls ready for the breeding season and insuring they are capable of doing the job they are there to do!

Insuring Fertility

Fertility in the cow herd, for both male and female animals is absolutely critical. Insuring fertility in the herd is having ALL the necessary components or factors in place that allow for the fertilization/impregnation process to occur on either the male or female side of the equation. In all mammals this is a factor of nutrition, age, health, stress, environment, endocrinology, temperament, etc.

Whether the producer uses a limited or year-round breeding season, he needs to understand the factors that affect the fertility of the bull and what strategies he can use to improve or maximize the fertility of the bull or bulls in his herd. This improves overall herd performance, individual calf performance and longevity of the bull's usefulness in the herd.

Fertility in a livestock enterprise is 5 to 10 times more important economically than any other production measure. While factors such as average daily gain, yearling weights and milking ability are all important, they are irrelevant if cows aren't bred and calves aren't born. Cows bred to high-fertility bulls bear more calves earlier in the season, resulting in more pounds of beef weaned and marketed per cow, which is a direct measure of profit. Bulls with identical semen quality in terms of physical assessment vary in actual fertility. The capability to identify bulls on the basis of fertility potential could result in higher pregnancy rates, leading to larger calf crops.

Step 1 - Breeding Soundness Evaluation

A very useful, important but underused tool to producers is the Breeding Soundness Evaluation (BSE). Important considerations include:

1) A Breeding Soundness Examination (BSE) is the best assurance of satisfactory bull fertility.

2) A bull should have a BSE done every year. It is good, inexpensive insurance.

3) Utilization of a BSE has the potential to return at least $20 for each $1 invested in the procedure. A bull may be big and masculine in appearance, but may not be a satisfactory breeder. A BSE provides the best evaluation of the bull's reproductive potential. Normally, a BSE should be done at least 45 to 60 days before the start of the breeding season. For the breeding season starting May 1, the BSE should be done between March 1 and March 15.

4) Bull fertility affects the pregnancy rate, average calving date, average weaning weight, uniformity of calf crop and age of puberty in replacement heifers — all of which have a significant effect on economic importance.

5) Bull scrotal circumference is positively related to both bull and heifer puberty as well as semen quality. This is largely a genetic issue.

6) Surveys report that 15-20 percent of bulls have problems which adversely affect fertility.

Detecting high fertility bulls (or identifying low fertility animals) is the key to increasing livestock production and thus profitability. Working with your veterinarian to properly evaluate your bull or bulls is a valuable tool and insures that your overall breeding program will not be diminished or delayed, both of which are extremely expensive.

To put this on a larger scale, a one percent increase in fertility in the U.S. beef industry would return a net profit of $55-60 million to U.S. producers. Obviously, on a global scale, billions of dollars of income could result from identifying higher fertility bulls and males of other livestock species. On a local scale, a rancher who bred proven fertility bulls to heifers in a higher ratio than usual–one bull to 20 heifers instead of the industry standard rate of one bull to 15 heifers–found that he got the same 92-95 percent pregnancy rate during the first 45 days while using a third fewer bulls and no additional feed.

Step 2 – Evaluating Stress, Nutrition and Excercise

On-going research by a group at KSU group is searching for ways to detect not only infertility in bulls but also to maintain fertility and maybe even improve fertility. The vast majority of cattle are still being bred naturally, and bulls are obviously an important part of the equation. Polls of producers and veterinarians have shown that about 20 percent of bulls have some sort of fertility problem. Unfortunately, relatively few bulls are tested for fertility so some (many) ranchers may not recognize that a problem exists and certainly do not know where the problem may be.


Fertility issues don't necessarily mean that bulls with these types of problems are sterile. They just have poorer calf crops than should be. Bull infertility can result from stress, caused by the weather, transport, handling, and so on as well as nutrition.

In some areas of the country extreme combination of cold temperatures and blizzard conditions during winter months is always a concern to cow-calf producers because of the added difficulty in feeding and caring for the cattle herd. Winters such as the one we are currently experiencing can be especially hard on bulls.

Herd bulls, which are generally kept separate from the main cow herd in those with limited breeding seasons, may experience hardship if proper nutrition and shelter are neglected. The future reproductive success of the herd will suffer if bulls are not prepared for or protected from winter weather. Bulls need to be maintained in a body condition score of 5-6 in order to be in ideal breeding condition. Low temperature and windy conditions can easily increase feed requirements 25-30 percent above normal maintenance requirements. Also, lack of wind protection and proper bedding will increase the chance of frost damage to the scrotum and testicles. During normal winter conditions frostbite is not a common problem with breeding bulls, but prolonged exposure to extreme cold and wind increases the incidence of frostbite and is a problem that must be considered when planning for the breeding season. Evidence of frostbite to the scrotum is usually apparent a few days after freezing in the form of noticeable inflammation and swelling. The heat generated from the inflammation directly affects the sperm that are maturing and stored in the epididymis, which surrounds the testicle at the lower end of the scrotum. The resulting damage may cause temporary or, in more severe cases, permanent sterility in the bull. A scab may appear on the lower portion of the scrotum as healing occurs. However, the absence of a scab does not indicate that frostbite injury has not occurred. Severe frost damage to the testicle and epididymis may cause tissue adhesions, affecting mobility and circulation within the scrotum.

Likewise, external heat or internal heat can be detrimental to bull fertility. Here are some ways to manage this problem. Bulls depend on a number of mechanisms to keep the testicles in optimal operating temperature. The mechanisms include the tunica dartos, cremaster muscle, counter current function of the pampiniform plexus and the testicular arterial branching. The important thing for producers and veterinarians to realize is when a heat related insult occurs, it is important to consider several things, including the severity of an insult, prognosis and what processes, whether pathologic or management-induced, are involved. These factors can affect the efficiency at which any of these reproductive related processes function, resulting in higher testicular temperature that can lead to increased problems with sperm formation and function. Increases in testicular temperature have resulted in reduced semen quality. Sources of thermal insult include high environmental temperature, fever and excessive lying down. Any of these conditions can negatively impact semen quality. The breeding soundness examination can help identify these potential problems.


Nutrition and feeding practice can have a profound affect on fertility. Fertility can be negatively affected by feeding certain materials such as excessive gossypol, the pigment in cotton products (cottonseed meal, cottonseed hulls, etc.). This does not mean that cottonseed by-products cannot be fed to bulls, only that they should be fed at moderate levels – no more than 3-4 lbs of cottonseed by-product feeds per head per day. The good news about this situation is that it is reversible. Research has shown that bulls with poor fertility due to the consumption of excessive gossypol will regain normal fertility several weeks after the gossypol is removed from their diet. Additionally, several studies have been done with vitamin E, an antioxidant and commonly included nutrient in feeds and mineral supplements, in combination with gossypol. Not only did the vitamin E protect against gossypol, it appeared to be favorable toward bull fertility. Other research into alleviating stress effects are being done with vitamin A, C and the trace mineral selenium.

In the last couple of years, the cattle industry has dealt with two significant factors that subsequently have affected the nutritional programs for many operations. One has been the droughts that have been experienced. The availability of forages, the base of any herd's nutritional program is severely affected by drought, causing producers to have to find alternative sources of forage. This has been coupled with exceptionally high feed prices meaning that not only have forages been hard to source in some areas, they have been extremely expensive in some areas as well. Additionally in many cases the forage sources that have been available have also been of very low quality thus requiring additional supplementation to meet the animal's needs. Supplemental feeds that would be needed have also been very expensive. Putting all this together, for many producers this meant feeding poorer forages than they would have preferred as well as lower amounts or quality of supplements simply because they had limited dollars to spend. This results in a less than optimal nutrition program and potential problems with fertility.

Energy intake can have a great deal of effect on the breeding soundness of bulls. Ideally a bull should be in a body-condition score of 6 to 7 prior to the beginning of the breeding season. In many cases young bulls purchased at production sales are in excessive body condition. If this is the case, it is recommended that young bulls carrying excess flesh should be "let down" from the time of purchase until they are turned out with the cow herd. It is suggested that the producer, when buying a new bull get information on the type of diet the bulls have been eating and then slowly step down the amount of concentrate and increase the percentage of forage over a period of 60 days. Avoid any major feeding changes.

Good management practices and providing balanced nutrients are critical for maintaining cow and bull fertility. In addition to protein and energy, adequate trace mineral intake and absorption is required for reproduction. Reproductive performance may be greatly affected if zinc, copper, manganese or selenium levels are marginal to deficient. In bulls, zinc deficiency causes lower fertility due to poor sperm quality and reduced scrotal circumference. Likewise, male reproductive performance is affected by low manganese status which can inhibits libido and lowers spermatozoa numbers. Another consideration for bull fertility is bone soundness and the ability to travel. Zinc, copper and manganese are needed for skeletal development and maintenance as well as hoof integrity. A bull suffering from lameness or joint problems will breed fewer cows. Selenium deficiency in bulls decreases spermatogenesis, the development and maturation process for sperm.

Feeding beef cattle complexed/chelated copper, zinc, manganese and cobalt has been shown to enhance reproductive performance early in the breeding season. Additionally, use of an injectable trace mineral such as MultiMin® three to four times per year (or at least 45 to days prior to the breeding season) can help overcome absorption issues and stimulate trace mineral-dependent reproductive processes.

As producers look at their mineral programs, two important considerations exist. First, the best approach to supplementation is to include a balance of all minerals that impact production and especially reproduction. Increasing the level of a single mineral due to identified deficiencies can create an imbalance, an antagonistic effect, on another mineral. For example, zinc and copper become antagonistic if either mineral is supplemented at extremely high levels. Optimum copper: zinc ratios are 1:3 to 1:5. Secondly, the strategic period for use of complexed trace mineral to improve reproduction and breeding performance in bulls is 60-80 days prior to the start of breeding season


Finally, exercise is important for bulls. Bulls have to be able to potentially walk miles in a given day. Plus during breeding, the energy level required can quickly wear a bull down if they are not is adequate physical condition. To increase the exercise level of these bulls feed them on a hill and provide water at the bottom of the hill. This type of exercise not only pulls any excess weight off these bulls, but it also strengthens the feet, legs and back.


Bull management to insure fertility and maximum productivity requires a considerable amount of understanding and input. The benefits are significant, however, when bulls perform optimally and provide the maximum genetic influence.

Dr. Steve Blezinger is a management and nutritional consultant with an office in Sulphur Springs, TX. He can be reached at or at (903) 352-3475. For more information please visit us on at www.facebook/reveillelivestockconcepts.

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