Managing Newly Purchased Yearling Bulls

Twig Marston
Extension Beef Specialist
Department of Animal Sciences and Industry
Kansas State University, Manhattan


Yearling bulls represent a large commitment to beef operations. Besides their purchase price, they are the future genetic material of the herd that can influence several generations of stock. Because yearlings still have a significant amount of growth and development ahead of them, they require a higher level of care and management than their older counterparts. This is especially true now as yearling bulls can possess considerably more genetic potential for growth than their ancestors.


Nutritional Management

One of the most common complaints of yearling bull purchasers is the run down condition these bulls can exhibit after their first breeding season. This situation can be largely avoided with good bull management. Whether the bulls were developed on the ranch, in a commercial facility, or at a centralized bull test, they were probably fed to gain from 2.5 to 4.0 pounds per day from weaning to one year of age. After coming off of test, and until they are turned out with females, they should continue to gain around 2.0 pounds per day.

Table 1 was created to show examples of diets formulated to grow yearling bulls at various weights. Dry matter intake, energy and protein requirements as well as diet formulation is provided as a management aid. Bulls grazing a grass paddock may need to receive 8 to 13 pounds of grain per day, similar to those on dry hay. Some will argue that bulls should not be pampered with grain supplements, but to insure a long and reproductive life, their basic nutrient requirements must be met. Quality of forage is extremely important to formulating proper bull diets. Many diet formulations can easily satisfy yearling bull maintenance and growth requirements. For example, some producers will allow bulls to graze cereal grain pastures with minimal supplementation, while others will have to feed a complete diet in a drylot situation.

Fat vs. Thin Bulls

If yearling bulls are fat they will need to be toned up before the breeding season. This may mean that energy intake will be set below the levels indicated in Table 1. However, fat bulls should not be let down too quickly, or their performance during the breeding season may be impaired. Conversely, thin bulls may need to be fed harder than indicated by Table 1. Ideally, yearling bulls should be purchased several months prior to their first breeding season so there is adequate time to prepare for the rigors of duties. At turn out time, ideally, a yearling bull should exhibit a body condition score of 6 (the upper end of moderate, scale 1 to 9).

Protein Requirement

After achieving their first birthday, bull’s protein requirements settle to about 10% of their total diet, depending on their dry matter intake. Usually this requirement can be met by adding one pound of a protein supplement per day to the grain portion of the diet. If high quality forage (pasture or hay) is fed, the additional protein supplement may not be needed. Forage testing and balancing the diet will pinpoint supplemental needs.

Mineral Requirements

Calcium and phosphorus are major minerals. Diets that contain approximately .40% calcium and .20% phosphorus are sufficient to meet dietary goals. The ration between calcium and phosphorus should be maintained at 2:1 or greater. In addition, trace mineral requirements should be met. Research has shown that feeding zinc at 60 ppm of the diet is beneficial to male reproduction. Other trace minerals like copper, manganese, and selenium should be monitored. Many commercial sources of trace minerals are available, but if desired a mixture of 40% dicalcium phosphate, 20% limestone, 30% trace mineral salt and 10% Selenium 90 premix can be used.

Vitamin Requirement

Any diet that includes high-quality, green forages should provide enough vitamin A to meet the yearling bull’s requirement. Vitamin A is inexpensive to feed, and therefore diet fortification near 30,000 IU per day would be cost effective. If forages are weathered and/or of low quality, an intramuscular injection of 3 million IU of vitamin A is advisable. Injectable vitamin A will maintain adequate liver stores for over 100 days.

Breeding Soundness Exam

All yearling bulls should have a complete breeding soundness exam (BSE) prior to herd turn out. A complete BSE includes a scrotal circumference measurement, a semen exam and a physical exam. Breeding soundness exam research has reported that bull with scores greater than 71 have a dramatically higher conception rate than those scoring 70 or less points. When compared to the cost of using a sterile or sub-standard bull, the money invested in a BSE is well spent. Table 2 can be used as a guide for minimum scrotal circumference measurements. Research indicates that bulls with larger scrotal circumferences are more fertile and tend to be more sexually mature than their lesser endowed contemporaries. Generally, bulls should have scrotal circumferences of 32 centimeters or more by their first birthday for breeding considerations.

Foot Care

A structurally sound, yearling bull should not require any foot care. Occasionally, however, foot rot, toe ulcers, and abscesses develop and require immediate attention. Excessive hoof growth may call for a foot trimming. If trimming is needed, it should be done well in advance of the breeding season (3 to 6 weeks) so the bull can recover from any soreness the trimming may have caused.


Exercise is important for good health and fitness. Many times yearling bulls need to harden up prior to the breeding season and the best accommodations are outside lots, fields or pastures. Bulls should be protected from severe cold and heat prior to turn out. Providing bedding during winter and spring storms will protest testicles from frost bite. Likewise, extreme heat can be detrimental to sperm production.



The newly purchased bull should be vaccinated against IBR, BVD, PI3, leptospirosis, and vibriosis. It is also a good idea to immunize him with a 7-way clostridial bacterin. The total cost of these vaccines are minor when compared to the cost of the diseases. Knowing the vaccination history will greatly influence your vaccination decisions. Bulls should also be treated for internal and external parasites.



Age and Size

Assuming all other factors are in good order (breeding soundness exam, body condition score, feet and legs, health, etc.) the newly purchased bull should be at least 13 months old and weigh a minimum of 1,100 pounds before being turned out for the first time. The older and larger he is, the better his chances are of coming through his first breeding season without problems.

Number of Females

Setting absolute guidelines for cow-to-bull ratio is difficult because there are several variables that have an impact on this number. Examples are a bull’s age, size, condition, and sex drive. Environmental factors like: size of the breeding pastures, type of terrain, climate, and length of the breeding season can also affect the correct cow-to bull ratio. Absolutely, a yearling bull will not be able to service as many cows as an older counterpart. As a rough guideline, however, the working range is approximately 10 to 25 females per yearling bull during a 45 to 60 day breeding season.

Length of Breeding Season

A maximum of 45 to 60 days is an ideal length of breeding season for yearling bulls. Ninety days is an absolute maximum. One method of saving wear and tear on a yearling is to turn him out after an older bull has been with the herd for the first one or two heat cycles. Some producers rotate bulls in and out of pastures to assure a lazy bull’s mates can get covered by another. Regardless of the management style, it is not advantageous to run yearling bulls with cows for long periods of time. They will waste a considerable amount of energy chasing cows and losing body condition instead of building up reserves for the next breeding season.


Try to observe the yearling bull closely to make certain he is detecting heat and breeding cows. Also, keep an eye on his condition. If he is getting too thin and rundown, he needs a rest. Thin bulls are more apt to hurt themselves, become less fertile, and have increased nutritional needs after the breeding season. Yearling bulls should not be pastured mated to cows that are extremely larger than themselves. Physically, this height mismatch may cause injury and failure to mate properly.

Running Multiple Bull Breeding Batteries

Research shows that when bulls are run together in a breeding pasture, they should be as close to the same size and age as possible. Larger, stronger, older bulls tend to dominate smaller, younger bulls and may prevent them from performing satisfactorily.




Yearling bulls will probably lose from 100 to 300 pounds during their first breeding season. In addition to gaining back this weight during their first rest, they must also gain enouch body mass as to achieve 75% of their mature weight by their second birthday. For example, if a bull’s potential mature weight is 2,000 pounds, he should weigh at least 1,500 pounds at two years. If he weighed 1,250 pounds at turn-out time as a yearling and lost 200 pounds during the breeding season, he would need to gain about 2.0 pounds per day during the nine months until his second birthday. In order to gain 2.0 pounds per day, coming 2-year-old bulls may need to be fed 13 pounds of grain, protein supplement, and a full-feeding of hay. High quality forages could be utilized to reduce the grain and supplement portions of the diet. A word of caution: do not try to bring a bull back too fast with too much grain because of risk of foundering him.

Health Management

In the fall, after the first breeding season, treat the bull for internal and external parasites. The following spring, when he is two-years old, deworm him again and give him annual booster vaccinations against the diseases listed earlier.

Table 1

Table 1. Feeding yearling bulls of varying weights to gain approximately 2.2 pounds per daya


Body Weight, pounds








Medium-quality hay, lb/day





Corn, lb/day





Soybean meal, lb/day





Limestone, lb/day





Dry Matter Intake, lb/day





Nutrient Composition:


NEm, Mcal/lb





NEg, Mcal/lb





TDN, %





Crude protein, %





Calcium, %





a Ingredient cost and availability will allow a wide array of correct diet formulations to be used.