I am a proponent of Artificial Insemination in dairy animals.  However, not everyone shares my enthusiasm for A.I. so I will concede if one is going to use natural service one should make sure the bull is capable of getting cows or heifers pregnant.

Natural service bulls should be taken to your veterinarian for a Breeding Soundness Evaluation (BSE).  The results of the BSE will predict a bull to be fertile, subfertile, or sterile.  Only bulls in the fertile category should be used.

A bull BSE includes the following four components:

 1) Physical exam;

Evaluates the physical characteristics of a bull necessary for mobility and athleticism, structural soundness, overall internal and external reproductive tract development, etc.

 2) Scrotal circumference:

Evaluates testicular size and health, as well as estimating the bull's sperm-producing capacity.  Bulls must meet minimum scrotal circumference measurements based on age in order to pass a BSE.

 3) Sperm motility:

Ensures that the bull is producing sufficient numbers of live sperm.  Bulls must have at least 30 percent motility to pass a BSE.

 4) Sperm morphology:

Ensures that the bull is producing sperm that are properly shaped and capable of fertilization.  Bulls must produce at least 70 percent normal sperm to pass a BSE.


The recommended minimum requirements for scrotal circumference, sperm motility, and sperm morphology are outlined by the Society for Theriogenology.


A BSE does not evaluate a bull's libido, nor does it ensure that a bull will remain a satisfactory breeder.  If a bull suffers injuries to his feet, legs, reproductive tract, etc., such an injury may render him incapable of breeding your cows.  Therefore, it is still extremely important to observe your bulls regularly to ensure they are doing their job.  A BSE also does not guarantee that bulls are free of infectious diseases, so consult with your veterinarian on what diagnostic tests may or may not be appropriate for your bull.


Author:  George Heersche, Jr., Ph.D.

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