AgWatch


Don’t Forget Your Herd Bull During The Calving Season

DR. TERESA L. STECKLER

SIMPSON, ILL.
   As I sit in my office I am thinking of the numerous bull sales that have occurred and those that are in the near future. Some cow-calf producers in southern Illinois may be just beginning to calve while others may have begun in January.  Probably the furthest thought in their minds right now is the herd bull. But the next breeding season will be here sooner than expected so plan ahead and manage you herd bull now. 
   Proper bull management, particularly nutrition and reproductive soundness, are vital to ensure the long-term viability of your beef cattle enterprise. Herd bulls contribute one-half of the genetics to each calf crop and without a functional bull that contribution and an adequate calf crop is not realized.  Therefore, proper and adequate nutritional management of herd bulls as well an annual breeding soundness evaluation before the breeding season is paramount to a successful breeding season and economic viability of the beef enterprise.
   If you purchased a new bull then you may be slightly ahead of the curve because these bulls are generally very fleshy and many consignors offer breeding soundness evaluation (BSE) results prior to sale. But remember these bulls generally have gone through a development phase which consisted of a high-energy concentrate based diet. These bulls must be transitioned from a test or development diet to a conditioning or maintenance diet that is often forage based otherwise they will fall apart.
   The transition/conditioning period should be around 60 days and is stressful for these bulls. This time frame should allow a sufficient amount of time for the bulls to adjust to the new diet. Well conditioned bulls during this time period will reduce their fat cover and “harden up”.
   If you are using your herd bull again this year, then it is advisable to conduct a BSE. Very few bulls are “sterile” and unable to produce any offspring. But, 10 percent to 25 percent of bulls have reduced fertility or possess physical problems which reduce their ability to sire calves. The BSE is a useful tool in identifying these bulls. Eliminating bulls with physical problems or reduced fertility from the breeding herd will improve overall reproductive efficiency of the herd.
   For the breeding soundness evaluation to be successful, bulls should be evaluated 30 to 60 days before the start of breeding. A complete BSE is normally conducted by a veterinarian and consists of a (1) physical examination (feet, legs, eyes, teeth, flesh cover, scrotal size and shape), (2) measurement of scrotal size and (3) semen evaluation for sperm motility (movement) and morphology (structure and shape). It is important to allow sufficient time to replace unsatisfactory bulls. Bulls could also be evaluated at the end of breeding to determine if their fertility decreased.
   The physical examination studies overall appearance. This part of the exam may be the most difficult to objectively assess. Some structural defects may have little or no influence on immediate mating ability but may predispose animals to early development of arthritis or injuries. Criticism of such defects often is taken as controversial opinion, but is important nevertheless. Aside from structure, flesh cover is another factor to evaluate. 
   Bulls can easily lose 100-400 lbs of body weight – equivalent to loss of 1 to 4 units of body condition. The amount of bodyweight 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. Ideally, bulls should have enough fat cover at the start of breeding so their ribs appear smooth across their sides. A body condition score 6 (where 1 = emaciated and 9 = very obese) is the target body condition prior to the breeding season. 
   The physical exam also includes feet and legs which are very important because if they are unsound, this can result in the inability to travel and mount for mating. The general health of the bull is critical since sick, aged and injured bulls are less likely to mate and usually have lower semen quality.  The external examination of the reproductive tract includes evaluation of the testes, spermatic cords and epididymis. Scrotal circumference is an important measure since it is directly related to the total mass of sperm producing tissue, sperm cell normality and the onset of puberty in the bull and his female offspring. Bulls with large circumference will produce more sperm with higher normality and also reach sexual maturity sooner.
   The standardized procedure of evaluation will result in a classification into one of three categories: “Satisfactory” potential breeder, “Unsatisfactory” potential breeder, or “Classification Deferred” (with a recommended date for re-evaluation).
   Any bull meeting all minimum standards for the physical exam, scrotal size and semen quality will be classed as a “satisfactory” potential breeder. Many bulls that fail any minimum standard will be given a rating of “classification deferred.” This rating indicates that the bull will need another test to confirm status. Mature bulls (that were listed as classification deferred) should be retested after four to six weeks. Mature bulls will be classified as unsatisfactory potential breeders if they fail subsequent tests.  Young bulls that are just reaching puberty may be rated as “classification deferred”, and then later meet all of the minimum standards. Therefore caution should be exercised when making culling decisions based on just one breeding soundness exam.
   Producers need to recognize that a BSE does not evaluate a bull’s breeding drive or ability. The producer should ensure that bulls, especially new ones, are observed during the breeding process and that they are interested and able to mount and inseminate females.
   Bull producers and buyers should understand the basis and protocol for a standard BSE. This will enable them to better interpret the test results and to ask questions about the procedures or the results. ∆
   DR. TERESA L. STECKLER: Extension Specialist, Animal Systems/Beef, Dixon Springs Agricultural Center, University of Illinois
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