By: Julie Walker, SDSU Extension Beef Specialist
Cattlemen can increase the breeding capacity of bulls through proper care prior to the breeding season. Because the production of sperm cells require 60 days with several factors having a potential negative impact on breeding ability, it is time to begin evaluating bulls now to ensure they are ready for the breeding season. Key components of a bull checkup are: 1) assessing body condition score, 2) breeding soundness evaluation and 3) physical soundness (structure and conformation).
Body condition score
Body condition score is a free method which allows producers to evaluate the nutritional status of animals. Assessing body condition score allows producers to determine if adjustment to the ration are required to ensure the bull is in breeding condition. Bulls should be in a body condition score of 6 on a 9 point scale (1 = being emaciated and 9 = being obese) at the beginning of the breeding season, since bulls normally lose about 100 to 200 pounds during the breeding season. Thin bulls (BCS ≤ 5) should be put on a ration with a higher level of energy, by replacing some of the roughage with energy dense feeds. Gradually increase the percentage of concentrate by 10% per week until reaching a ration that will achieve a rate of gain that will increase body condition. This must be a gradual process to avoid nutritional disorders associated with over-feeding grain such as acidosis, founder, or bloat.
Over conditioned bulls (≥ 7 BCS) should be provided less energy dense rations. Bulky feeds such as forages should be used to replace grain. Again, these changes should be made gradually. Remember yearling bulls should continue to gain 1.5 to 2.0 pounds per day, because they are still growing. Additional information on nutrient requirement is available in iGrow Beef: Best Management Practices for Cow-Calf Production.
An annual breeding soundness examination of each bull is the only way to predict that bulls will be reproductively sound during the breeding season. These examinations are conducted by veterinarians. The components of a breeding soundness examination include 1) measure of scrotal circumference, 2) sperm motility, 3) sperm morphology, 4) testicle palpation, 5) palpation of seminal vesicles, and 6) observation of physical problems. Research has shown that bulls with a large scrotal circumference have greater breeding capacity and endurance. They also produce daughters that reach puberty at an earlier age. Palpation of the testicles and seminal vesicles is looking for any possible infection or defects that could impact the amount or quality of sperm.
Sperm motility and morphology are examined under a microscopy at the time of collect. Sperm motility is the measuring the percentage of sperm with a progressive (headfirst) movement and sperm morphology is the percentage of normal sperm in the ejaculate. If you would like to see an example of sperm motility and morphology watch the SDSU iGrow semen handling video.
Evaluation of the physical soundness of bulls is critical for a successful breeding season. Bulls use both eyesight and smell to aid in detection of estrus, hence the importance of evaluating eyes. The structural soundness of the feet and legs is imperative due to the amount of exercise (walking) as well as the mounting of cows/heifers. Mobility evaluation within a squeeze chute is difficult, so it is key to observe bulls walking.
The bottom line
Producers invest substantial amount of money in bulls to continue improvement in the genetics of their operation. Ideally, that investment can be utilized in multiple years. Taking steps now to ensure that the bull battery will be ready for the breeding season allows producers adequate time to implement any required changes or the purchase of additional bulls.