Cattle Today

Cattle Today



by: Matt Hersom and Todd Thrift
University of Florida

Bulls, purchased or home raised, are large capital investments that need to guarantee a return on the investment. However, the bull is often the nutritionally forgotten or most marginalized component of the beef cattle enterprise. This is unfortunate because proper bull management, particularly nutrition, is vital to ensure the long term viability of the beef cattle enterprise.

The bull contributes one half of the genetics to each calf crop; without a functional bull that contribution and an adequate calf crop is not realized. Therefore, proper and adequate nutritional management of the herd bulls is paramount to the breeding season success and economic viability of the beef enterprise.

Nutritional management of the herd bull necessitates planning to ensure success. In light of the tightening of feed supplies, adequate planning is both nutritionally and financially imperative.

Nutritional Management of Beef Bulls

There are a number of well defined nutritional periods during a bull's life:

1. Pre puberal pre weaning.

2. Pre puberal post weaning to 30 to 60 days pre breeding.

3. Conditioning prior to the breeding season.

4. Management during the breeding season.

5. Management after the breeding season.

Pre weaning: During this period, the bull is at the dam's side and nutrition during this period is likely adequate to ensure normal growth and development. Exceptions would be indicated when the dam's nutritional environment limits milk production.

Creep feeding of potential herd sire bulls is utilized in some instances. Currently, there is little or no data that have evaluated the long term effects of creep feeding on bull performance.

Post weaning: This period of nutritional development should allow the bull to grow at nearly the bull's genetic potential. The nutritional design of many growing programs or bull test station diets is a concentrate based, low roughage, high energy diet. The goal of this period is to grow the bulls rapidly, but avoid excessive fat development.

The nutritional program should also be designed to avoid digestive upsets or affect soundness. The high energy, high plane of nutrition also stimulates the onset of puberty, particularly in later maturing breeds. Adequate research indicates that either under or over nutrition during this period can have detrimental effects on bull development, attainment of puberty and semen quality.

Well designed bull test diets or purebred bull breeders with sound development programs should allow bulls to express their growth potential without any deleterious effects on future performance.

Conditioning prior to the breeding season: This period is the most important next to the development phase, but that could be debated. Not only do growing bulls need this conditioning period, but mature bulls need to be conditioned before entering service during the breeding season.

Growing bulls generally have just gone through the development phase which consisted of high energy, concentrate based diet. As such, these bulls need to be cycled down from that high plane of nutrition. That means there needs to be a transition from the test diet or development diet to a conditioning or maintenance diet that is often forage based. The transition to a forage based diet often occurs when the bulls are losing their teeth, compounding the stress of the diet transition.

The conditioning period should be around 60 days. This time frame should allow adequate time for the bulls to adjust to a new diet. For well conditioned bulls, this time frame will allow bulls to moderate their fat cover and "harden up;" likewise thin bulls will have adequate time to increase their body condition if required.

Additionally, the 60 day timeframe provides adequate time for the sperm population to turn over and quality sperm to develop prior to the bull entering breeding service. The bull should enter the breeding season in a body condition score of 5.5 to 6.5 (9 point scale). This body condition score provides the bull adequate body reserves to draw upon during the defined breeding season.

Nutrition during the breeding season: The nutritional environment during this period is almost always the same as the cowherd. Therefore, special nutritional attention for bulls is nearly impossible. As a result, the conditioning period prior to initiation of the breeding season becomes all the more important.

Bulls, during the breeding season, can lose from 100 to 400 lbs. of body weight which equates to a loss of 1 to 4 units of body condition score. The amount of body weight and body condition loss will be influenced by the age of the bull, prior body condition, length of the breeding season, level of activity experienced by the bull, and breed type of the bull.

Young bulls and terminal sire type bulls in the Gulf Coast environment will likely lose more body weight and condition during the breeding season compared to older or maternal type bulls in the Gulf Coast environment.

Nutrition after the breeding season: The bulls, after the breeding season, likely will need some attention to restore their body weight and body condition. The amount of body weight and body condition that needs to be replaced after the breeding season can be considerable, depending upon how much body weight and body condition the bull mobilized.

A 2,000 lb. bull that loses 200 pounds could require up to 1,200 lbs. of 65 percent TDN feed to fully regain all of the body weight that was mobilized. As mentioned previously, young bulls and terminal sire type bulls likely will lose more body weight.

Greater body weight loss by the bull will result in greater amounts of nutritional inputs that will be required to regain bull body weight. The length of the breeding season and length of the resulting recovery period will dictate the intensity of feeding to recover the lost body weight.

Maternal sire type bulls are likely to be expected to regain body weight on pasture alone or with minimal supplemental feed. Terminal sire type bulls may require supplemental feeds to regain lost body weight because pasture quality may not support the needed performance. Likewise, the use of young bulls that still have growth requirements will likely result in greater feed input requirements after the breeding season.

Transition Timeframe Considerations

As mentioned previously, the transition of a purchased bull from a test diet to a normal production type diet is critical. An assessment of the bull's previous level of nutrition and its characteristics on his current and future performance needs to be made.

Often, bulls come off of test diets rather well conditioned (i.e. fat, body condition score of 7+). While that conditioning may have been appealing in the sale ring, it will not be that great of an asset breeding cows on the ranch. How fat is the bull and how much fat needs to be shed and replaced by lean muscle is the issue?

Excessive condition can be detrimental to semen quality because fat deposition decreases the effective cooling of the testes. Likewise, excessive condition going into the breeding season can set the bull up for failure as the increased activity level and reduced feed intake cause him to "melt" as the breeding season progresses.

Therefore, the goal of the transition period should be to adapt (let down) the new bull from a high energy concentrate diet to a low to moderateenergy, roughage based or grazing diet over time. Continue the growth pattern as needed and adapt the bull to an elevated activity level.

The transition between diets should occur over several weeks to provide adequate time for the bull to adapt to the new diet. In that regard, the bull will need to receive a diet not that different from the test diet when he arrives at the ranch.

A supply of similar concentrate feedstuffs will need to be on hand for the bull upon arrival. The transition at the ranch could begin with a diet that contains 60 to 70 percent of the previous concentrate intake and then be decreased gradually over a number of weeks until the final diet formulation is reached. Therefore, it is imperative that planning go into the purchase, nutrition and overall management of a bull prior to his use during the breeding season.

Replacement of the concentrate portion of the ration can be replaced by bulky, fibrous feedstuffs (soybean hulls, citrus pulp) or replacement with moderate quality hay or silage.

Remember, young bulls still have a growth requirement and likely still need to gain 2.0 to 2.5 lbs./day of body weight during the transition. Therefore, depending upon the quality of the forage base utilized, complete removal of the concentrate portion of the diet may not be completely feasible.

The concentrate portion of the ration generally supplies the energy and most of the protein to meet the bull's growth requirement.

The body weight gains of bulls during the transition period is dependent upon a number of factors that include previous body weight gain, current body weight, current body condition. and desired body weight at the initiation of the breeding season. Gain achieved is then determined by dry matter intake, diet energy and protein density.

Bulls that are undersized for their desired breeding season body weight will need to be developed during the transition period at a greater rate of body weight gain compared to more fully developed bulls. In contrast, bulls that are overly conditioned but are not fully mature still require a positive plane of nutrition, albeit one that emphasizes lean body weight gain rather than fat deposition.

To that end, rations that are high in roughage content or utilize quality pasture, moderate the readily available carbohydrate concentration and provide adequate protein are desirable.

Another important consideration during the transition period is exercise. Likely, bull test animals came out of confined spaces/pens and are not acclimated to open space. Provide the bull adequate space to exercise and become accustom to a level of exercise.

If the pasture size is adequate in size, water, feed and mineral can be spread around the pasture to encourage a level of activity prior to the breeding season. An increased level of activity may increase the bull's nutrient requirements by 5 to 10 percent, so appropriate consideration should be given.


Key nutritional time frames exist in the lifespan of the bull in the beef herd. The appropriate nutritional management of growing bulls is a key component to the long term reproductive success of the beef cowherd. Like much of the management of beef cattle, the transition periods are management situations that can have significant effects on the success of the bull management program.

During the transition periods, the prior nutritional status, current body condition and body weight growth goals of the bull all need to be considered when designing a bull nutrition management program.

The take home message is, know your bull; what breed type is he, what is his current body weight/body condition, his expected mature body weight because that affects nutrient requirements, and what are his current nutrients requirements and his needs for a given production scenario.

Editor's Note: This article is Part I of a two part series on managing bull nutrition in commercial operations.


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