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Don’t Forget to Test Herd Sires Before Breeding Season

May 1, 2017

Herd bulls will soon be running with the cowherd and breeding season will begin, starting a new cow/calf production cycle. Yet, before turning out sires, make sure they can do their job effectively by conducting breeding soundness and health exams to help aid in their success this breeding season.

Breeding Soundness Examination
Breeding soundness examinations (BSE) include a physical exam (evaluating internal and external genitalia), scrotal circumference and semen exam. BSE’s should be conducted 30 to 60 days prior to the beginning of the breeding season in order to allow time for retesting if necessary. In order to pass a BSE, a bull must meet minimum criteria in each part of the exam in order to determine if he will be able to efficiently service cows.

Physical Exam
Physical exam begins with evaluating the health, body condition and conformation of the bull to answer questions such as: Is he healthy, in adequate body condition, and structurally sound to mount cows and move around the pasture? The physical exam also includes palpation of internal and external genitalia for abnormal adhesions, inflammation or abscesses that may impact his breeding ability or spread disease. Remember BSE’s do not measure libido; therefore, bulls should be frequently monitored in a breeding environment to ensure the desire is there and that he can fully insert and complete the breeding process. If bulls have any problems servicing cows, detecting cows in heat, or trouble with mobility and maintaining BCS, then a replacement should be found as he likely is not the bull you want servicing cows.

Scrotal Circumference
Scrotal circumference is measured during a BSE as an indicator of puberty and is utilized to set a minimum standard scrotal size to be reached at a certain age (regardless of breed). For example, to pass a BSE yearling bulls must measure 30 centimeters and 2 year-old bulls must have 34 centimeters.

Semen Evaluation
During a BSE, a veterinarian utilizes electro-ejaculation or manual stimulation to collect a sample of semen. This semen sample is then evaluated for motility and morphology, but not concentration. Motility evaluates the forward movement of the sperm in the sample and must have a minimum of 30% progressively motile sperm to pass. While this percentage seems low, differences in semen handling (processing and temperature) play a large role in variation between samples, thus the passing rate was adjusted to account for these differences. Morphology is an evaluation of the size, shape, development of the sperm cells, where 70% normal cells are needed as a minimum to pass. For this reason, morphology is commonly the section of a BSE where most bulls fail.

BSE Results & Ecnomoics

Bull Classification
After all sections of a BSE have been conducted, bulls are classified as satisfactory (if they pass all exams) or unsatisfactory potential breeders (fail to meet either one of the physical exam requirements or minimum semen evaluation values). In addition, if a bull fails in one minimum value of the BSE, veterinarians can classify them as “deferred” and retest 14 to 30 days later.

Although a producer is not required to have a BSE conducted, a $50 test equates to only $1 to $2 per cow exposed to that bull. If bulls are infertile and several cows come up open, that expense would be much more devastating. The risk lies more in small herds with only 1 or 2 bulls servicing all the cows. Therefore, no matter the size of an operation, bulls should be tested prior to breeding season to avoid turning out infertile bulls which could be disastrous to season

Reproductive Disease Tests
All non-virgin should also be tested for reproductive diseases before the breeding season. Bovine trichomoniasis or “trich” made a resurgence in several areas of SD last year causing early and late term abortions across the state and country. Trich is a venereal disease caused by a protozoal organism that lives in the sheath of a bull and can be passed to a female through the act of mating. Once infected, the organism will cause inflammation of the female reproductive tract that results in the loss of a pregnancy. Bulls remain positive for life and should be eliminated from the herd. To determine if an exposed bull may have trich, a swab of the sheath can be taken by a veterinarian and submitted to a lab for evaluation. If at pregnancy check time an uncommon number of cows are determined to be open, this may be a reason to test all bulls for possible trich infections.

The Bottom Line
At the end of the day, a bull’s job is to get cows pregnant and a BSE is one way we can determine if they are satisfactory breeders before turning them out with the cow herd. Remember, a BSE is not good for life, since a passing score means that bull is fertile only on that day. However, physical and environmental injuries, or diseases could affect future fertility; thus BSE’s should be conducted every year. Consult with your herd veterinarian, seed stock supplier, and nutritionist and SDSU Extension livestock specialists for assistance in preparing bulls for the breeding season.

Source: Taylor Grussing, South Dakota State University, iGrow