by: Stephen B. Blezinger

About this time of the year, many producers are well into their calving season and many have already begun turning bulls back out with groups of cows to begin the breeding part of their program. In most cases, your bulls are the most costly animals on a cow-calf operation and provide the majority of genetic improvement for the cow herd (50 percent of each calf). It is extremely important for these animals to be healthy and in top physical condition to begin and carry out this process. Unfortunately, many producers may simply maintain their bulls through the non-breeding portion of the production year and automatically believe these animals are ready to go once the season is here. That may or may not be so. A number of important steps need to be taken to insure the bulls are in the best shape possible to re-enter the breeding herd and maximize their performance. This article will discuss these steps.


Bulls can be a challenging group of cattle to provide proper nutrition. They are a relatively small group compared to your herd as a whole and they can take up a lot of space. The tendency for many producers is to run all bulls together and hope that they won't do much damage to the facilities or each other. But, nutritional needs vary due to age and condition, so if young and old bulls are run together some bulls may not get the nutrition they need and others may get too much. There may also be injuries from fighting as the group establishes its pecking order.

Having bulls in the proper condition as they enter the breeding herd is critical. Bulls do not need to be under condition (too thin) or over conditioned (too fat). Either of these can create performance problems. It is important to monitor bulls throughout their “off-periods” to make sure they are in a proper body condition at least 60 days prior to breeding. Research has shown that for sperm cells to fully develop takes approximately 60 days under proper health and nutrition conditions. This means that at least two months prior to putting bulls back in with the cow herd they must be in proper condition for reproductive performance and in this case for proper sperm development.

This said, a correctly balanced diet must be provided for these cattle to insure proper nutrient levels in the animal. The diet or rations fed to these bulls prior to the breeding season will depend on forage types and availability as well as provision of protein and energy supplementation as necessary. Make sure that thin bulls are not pushed to fast with a high concentrate diet. Acidosis, abomasal ulcers, liver abscesses or seminal vesiculitis can ruin a bull prior to the breeding season if concentrates/supplements are not managed properly. A nutritionist can help you balance your supplements to your forages to meet these goals.

Below are some other considerations.

1) Minerals

One very important component for sperm development is mineral nutrition. Minerals must be properly balanced to insure the animal's reproductive system is functioning well and will produce sperm cells in the proper number and quality. For instance, it has been known for some time that a deficiency of zinc can reduce male fertility. Zinc plays a role in the production, storage, and secretion of individual hormones as well as in the effectiveness of receptor sites (McDowell et al., 1993). Zinc affects the production and secretion of testosterone, insulin and adrenal corticosteroids. Spermatogenesis and the development of the primary and secondary sex organs in the male are impacted by dietary zinc levels.

To expand on this a bit, a study by Arthington and co-workers in 1995 showed differences not only in the level of zinc fed but in the type as well. Bulls fed 60 ppm of zinc had higher liver zinc concentration than bulls fed 40 ppm of zinc supplied by zinc sulfate. But the bulls fed the 60 ppm of zinc had similar zinc liver concentrations to bulls fed 40 ppm zinc supplied by 1/3 zinc proteinate (an organic zinc source) and 2/3 zinc sulfate. There were no differences in average daily gain or scrotal circumference. The percentage of normal sperm cells was highest for the 40 ppm of zinc supplied by 1/3 zinc proteinate and 2/3 zinc sulfate (68.9 percent). Percent normal sperm cell levels for the 60 ppm zinc levels and 40 ppm zinc level supplied by zinc sulfate were 62.5 percent and 55.8 percent, respectively.

The use of organic zinc in growing bull diets may improve subsequent fertility measures. There are a number of different organic zinc (and other mineral) sources available on the market and there is no definitive research showing which of these sources is the best for bulls. However, inorganic zinc at an increased level (60 ppm) also improved fertility. One important point this study made was that for growing bulls, the NRC-recommended level of 30 ppm (13.6 mg/lb) in the diet may be too low. Zinc is not the only critical mineral for bulls. As with all animals, bulls require a full range of minerals and vitamins to complete their diet. A shortage of even one can make that particular nutrient the most critical if under supplied.

Another practice that is becoming increasingly common is to inject bulls with a trace mineral solution such as MultiMinTM prior to the breeding season. MultiMinTM includes levels of Zinc, Copper, Manganese and Selenium and can effectively raise trace mineral levels when used in combination with a sound total mineral program. Injections should be given 60 to 90 days prior to the breeding season.

2) What to Feed

Other considerations should be given to WHAT is being fed to bulls. Care should be taken when feeding cotton products (cottonseed meal, cottonseed hulls, cottonseed) to bulls. Cotton products include a chemical (pigment) known as gossypol. Gossypol is a naturally occurring substance found in the pigment glands of cottonseed that can be toxic (Lusby et al., 1991). Whole cottonseed has a significantly higher level of free gossypol than meal or hulls. Concern about feeding gossypol-containing products to bulls arose when Chinese researchers discovered that gossypol is a potent male contraceptive in humans. Gossypol appears to be more damaging to reproductive function in young males near puberty than to older, mature males. Studies where bull fertility has been reduced have involved feeding cottonseed products at high levels and/or for long periods of time (Chase et al., 1989). Research has also shown that the effect is reversible. In other words, if bulls were fed high levels of cotton products for an extended period of time and that it did have a negative effect on fertility, removing the cotton products from the diet would allow normal fertility levels to return.

Generally, however, feeding three to five pounds of cottonseed meal as a protein supplement to bulls is unlikely to expose the breeding animals to the levels of gossypol needed to cause productive problems (Martin, 1990).

3) New or Young Bulls

In many cases, the bulls being turned out are young bulls which the producer has purchased either in the fall or more recently in the spring to replace older bulls or to bring new genetics into the herd. Many yearling bulls come out of feeding programs targeting two to four pounds of gain per day (perhaps more in an effort to show genetic potential) from weaning to sale day. Bulls on high energy diets need to be "let down" from the time they are purchased until they are turned out with cows. A common mistake made occasionally is to turn the bulls that have been on a high grain ration out on very lush pasture or place them on straight hay. This can lead to digestive upsets or imbalances, thus leading to potential reproductive problems or to these bulls “falling apart”. These bulls should continue gaining about two pounds per day from arrival until turned in with the cows. They are still growing and maturing and need extra energy reserves going into the breeding season. These young bulls should be turned in with lower numbers of animals and should also not be paired with groups of older, more aggressive bulls.

Bulls should be in a body-condition score of 6 prior to the start of the breeding season. It also may be necessary to continue to supplement the breeding group to insure proper nutrient levels not only for the bulls but for the cows as well.


Prior to starting the breeding season, bulls need to be in good health. One effective tool in determining the animal's health and breeding soundness is a Breeding Soundness Exam (BSE). A breeding soundness exam (BSE) is critical to determine if the bull will be capable of getting cows bred this year. A BSE should include a good physical exam paying close attention to eyes and feet and legs. Bulls need to be able to see and travel in order to breed cows. Bulls need to be able to travel freely, so pay attention to feet and leg problems. Long or curled hooves could be a result of nutrition, genetics or a combination of the two. A bull walking on smooth, level ground should put his rear hoof down in the track left by the front hoof.

The testis and seminal vesicles should be palpated to make sure they are normal. Lastly the semen should be evaluated for morphology and motility (indicators of quality). If a bull does not have normal active sperm he can be re-evaluated in 30 days. If BSEs are delayed there is no time to correct any abnormalities and re-evaluate.

Extremely cold winter (not a huge problem this year) may have damaged the testis of bulls if they did not have adequate dry bedding. Frostbite of the scrotum will not have any long term effects but if the epididymis was damaged the bull will no longer be a viable breeder.

Know the vaccination history of purchased bulls, and administer vaccines or boosters against respiratory and reproductive diseases as needed, and treat for parasites if needed.

If new bulls are being brought onto the operation they should have a BSE if they have not already had one recently. All new bulls should also have been tested for Bovine Viral Diarrhea Virus (BVD) and Johne's disease. If new bulls are not virgin bulls, they should also be tested for Trichomoniasis prior to breeding any cows. A vigorous preputial scraping with a sterile plastic infusion pipette is the best sample to detect Tritrichomonas foetus in bulls. Your veterinarian should be able help you with these evaluations.

While the bull is in the chute for the BSE it is a good time to vaccinate and de-worm them. Vaccination with a modified live respiratory virus vaccine should be done at least 30 days prior to the breeding season so spermatogenesis is not impacted. Also vaccinations for clostridia and reproductive diseases such as Leptspirosis and Vibriosis are also a good idea. Although most mature bulls do not have severe internal parasite problems during the breeding season they cannot afford any nutritional drain from parasites.

Physical Condition

Another overlooked aspect of bull management is their physical condition. Bulls should be in good flesh but not overly fat going into the breeding season as they will lose weight during the breeding season. Bulls should be in good physical shape as they will need to travel extensively during the breeding season. The most efficient method is to put the bulls in large pasture with the water at one end and feed or salt at the other to force the bulls to walk. Bulls kept in a small pen or pasture and do not require much exercise will result in a bull that is essentially a “couch potato.”

Finally, if problems turn up, it is not too late to purchase a new bull, but time is short. Avoid the temptation to just get any bull to “settle the cows.” Poor-performing bulls or bulls with poor EPDs are a liability that most producers can't afford.


Like an athlete preparing for a competition, bulls should be prepared and “trained” prior to entering or reentering the herd. Taking the steps indicated above can greatly help with his readiness to perform and insuring that the cow herd will perform properly during the breeding season and then later during calving.

Dr. Steve Blezinger is and nutritional and management consultant with an office in Sulphur Springs Texas. He can be reached at 667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992 or by e-mail at You can also visit us on Facebook at Reveille Livestock Concepts.

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