Yearling bulls should have a BCS of 5.5 to 6.5 (on a 9-point scale) at the start of the breeding season. As purchased bulls arrive at the ranch, assessing BCS (fat level), knowing previous nutritional management and making a nutritional management plan for overly conditioned or underconditioned (thin) bulls is needed.

Upon arrival, the nutrition goal for each operation should be focused on transitioning the bull from a high-energy concentrate diet to a low- to moderate-energy, roughage-based or grazing diet over time. The transition should occur over several weeks to provide adequate time for the bull to adapt to the new diet.

With that in mind, when they arrive at the ranch, new bulls should receive a similar ration to the bull-development ration used by the seedstock producer. The initial receiving ration could begin with a composition that contains approximately 60%-70% of the previous concentrate (e.g., corn, barley, etc.) intake, which can then be decreased gradually over the next several weeks until the final ration composition is reached.

Gradual changes in concentrate are needed to reduce the possibility of decreased ruminal health or metabolic disorders, as well as impaired breeding performance.

With each step down in ration, replace a portion of the concentrate in the ration with forage over several weeks until the bulls are either consuming primarily forage or forage plus a supplement. Keep in mind, yearling bulls should still be growing approximately 2 pounds (lb.) per day during this period. Depending on the quality of forage, a total forage diet may not always be feasible to achieve certain transition goals, and additional supplementation may be needed.

Effects on fertility

Implementing these nutrition strategies for when bulls arrive at the ranch is critical for future sperm development and quality. Spermatogenesis is a continual process. Roughly 61 days are needed for sperm development, which is followed by up to a 14-day residence in the epididymis prior to ejaculation. Due to this length of time, previous over- or undernutrition coming into the breeding season can have a negative effect on sperm quality and quantity.

Ideally, transition feeding should start at least 45-60 days prior to turnout. Therefore, planning is imperative to successfully transition newly purchased bulls and prepare them for the upcoming breeding season.

Marathon training

I think about preparing a newly purchased yearling or 18-month-old bull for the breeding season as preparing for a marathon. If you are running a full marathon today, getting off the couch and running without any training wouldn’t result in the best performance.

There is always a level of training that must occur, depending on the current level of conditioning prior to the event. The same philosophy can be used for training or conditioning bulls prior to the breeding season.

Essentially, we want to shed fat and replace it with lean muscle. Some may call this “hardening” up a yearling bull prior to breeding. Yearling bulls come out of confined feeding spaces and sometimes are not well-acclimated to exercise. During the breeding season, bulls will travel up to 6-7 miles per day, depending on the size of the pasture.

Once those purchased bulls arrive, we want to provide them with adequate space and the ability to travel. A good practice to encourage travel is to spread out the locations of water and feed. Feed in the opposite corner of a pasture from the water source. The level of the adaption to the new environment may vary from one operation to another due to differences in terrain, stocking density, pasture size, etc., in which the new bulls are expected to perform.

Bulls that are not properly conditioned for the breeding season or that are overly conditioned going into the breeding season can lose up to 400 lb. during the season. Research from North Dakota State University has shown that bulls in a negative energy balance will decrease bull scrotal circumference over time.

The effect on sperm quality is still unknown. However, new research from the USDA Meat Animal Research Center (USMARC) in Clay Center, Neb., indicated yearling bulls have reduced sperm production after a 28-day breeding season.

Although body weight loss wasn’t determined in that study, overly conditioned yearling bulls losing large amounts of weight during the breeding season may have a larger effect on sperm quality and result in a shorter effective breeding season.

Takeaway

Prior to your bull’s arrival, have a nutrition plan in place, including having commodities needed on hand. A key to nutrition management postarrival is a slow change in diet from high-grain to a forage base so there isn’t any negative effect on semen production and quality, which affect early breeding success. Allow for adequate space and room to allow bulls to exercise and start becoming conditioned to traveling prior to bull turnout.

Editor’s note: “The Digestive Tract” is a regular column focused on nutrition for the beef cattle life cycle. Our team is happy to welcome Travis Mulliniks as the newest contributor to this column. Mulliniks is the Glenn & Mildred Harvey Professor of Beef Cattle Management, as well as the associate head of the Department of Animal and Rangeland Sciences, at Oregon State University.