Bull Breeding Soundness Evaluation

Lakeview Animal Hospital

Updated May 2011

Breeding soundness evaluations (semen testing) are a proactive approach to determine your bulls breeding capabilities. One can also look at their pregnancy and/or calving rate but this is an after the fact evaluation. A breeding soundness evaluation is a snapshot of the bull’s ability to breed. Knowing this can help you determine if more bull power may be needed for the upcoming breeding season or what bulls need to be culled from the herd.

What does a breeding soundness evaluation consist of? Basic exam for soundness, conformation, body condition of bull, and other obvious physical defects such as bad eyes or feet may be noted.  Scrotal circumference, sperm motility and sperm morphology are also evaluated.

Scrotal Circumference

Scrotal circumference is a measurement of the testicular size. A larger scrotal circumference positively correlates with increased sperm production of the bull and his sons, as well as earlier onset of puberty and increased fertility in his daughters.  Most breed standards recommend scrotal circumference to be 30 cm in bulls less than 15 months, 31 cm in bulls 15-18 months, 32 cm in bulls 18-21 months, 33 cm in bulls 21-24 months and greater than 34 cm in bulls over 24 months old. Many breed associations and veterinarians recommend only using bulls with 32 cm or greater scrotal circumference for breeding.

Sperm Motility

Sperm motility is the evaluation of the sperm’s ability to move in a forward manner. If it is unable to do this then the likelihood of a cow being bred by that bull greatly diminishes. Sperm motility should at least be 30% of sample having forward motion to be considered acceptable for breeding purposes.

Sperm Morphology

Sperm morphology is the evaluation of sperm size and shape. Sperm are produced in the testicle and develop in the testicle and epididymis (the button). Changes seen on evaluation can determine where the problem may be occurring if large amount of sperm are abnormal. Abnormal sperm are less viable and unlikely to result in pregnancy. Defects can occur in either development of the sperm in the testicle or with maturation of the sperm in the epididymis. Defects originating in the testicle are called primary defects and those originating in the testicle are called secondary. Both are equally important and no more than 30% of sperm should have either a primary or secondary defect to pass the exam.

Physical Exam

A general physical exam is done as the bull comes through the chute. If the bull is unsound he may be incapable of mounting a cow or traveling on the range either to the cows or to feed and water.  Also if a bull has a scarred or damaged eye he may be unable to locate cows, have a hard time finding feed and water, or be painful. The physical exam looks at the bull’s ability to physically mount a cow or survive on the range. If he is unable to travel to graze or drink the loss of body condition alone can cause infertility. The exam may also pick up heritable defects such as corkscrew claw.

As the exam is a snapshot, a bull’s semen quality may change. Young bulls that fail their first test may continue to improve and pass subsequent tests. Conversely a bull that passed may later on fail. Many things can affect sperm production including extreme weather, poor nutrition, illness, and physical injury.  If a bull fails he can be retested in 30-60 days to evaluate the new sperm that has been produced. A breeding soundness exam can be a very useful and cost effective tool for managing your bulls and cow herd.