Bulls are common on many beef operations. It is estimated that 90% of beef producers utilize a bull for breeding purposes. Therefore, the reproductive efficiency of the operation is dependent, not only on the reproductive efficiency of the dam, but also the sire. However, many producers do not have a breeding soundness examination conducted on their bulls. Often times the female is blamed for her inability to get pregnant.
Many factors can affect the reproductive capacity of a bull. Therefore, a breeding soundness examination should be conducted:
•With a new purchase
•On all new bulls
•Prior to semen collection for artificial insemination use
•Prior to sale
•If infertility or pathogen is suspected
Breeding soundness exam
What is a breeding soundness examination? A breeding soundness examination is an exam conducted by a veterinarian or trained professional in which they assess the fertility of the bull.
What is being assessed when a breeding soundness exam is conducted?
The overall condition of the bull including body condition score, feet and legs, and the eyes should be assessed for ulcers/cloudiness.
The condition of the reproductive anatomy should also be assessed. This includes palpating the testicles and observing the scrotum for scar tissue.
The motility and morphology of the sperm cells also needs to be assessed.
Why do these factors need to be assessed during a breeding soundness examination?
Body condition score of the bull is assessed because during the breeding season a bull will eat less and pull energy from fat reserves. It is not uncommon for a bull to lose up to 150 pounds in one breeding season. If the bull goes into the breeding season with too little condition he may come out of the breeding season under-conditioned.
Feet and legs are assessed to guarantee the bull is able to walk the pasture and get to the females that need to be bred. Eyes need to be assessed to ensure that the bull is capable of seeing the females that he needs to breed.
The scrotum should be evaluated for scar tissue as this thickened area of skin will interfere with testicular cooling.
Testicles should be palpated to check for firmness, soft testicles are a sign of degeneration and errors in spermatogenesis. Scrotal circumference is often taken to assess the sperm output capacity of the testicles. The larger the scrotal circumference, the more sperm produced. Scrotal circumference in mature bulls should be greater than 30 centimeters.
The penis should be observed for spiral deviation, persistent frenulum, penile hair rings, warts, and other defects that affect the bulls' ability to mate. The motility of the semen sample should be assessed to guarantee there is forward progressive motion of the sperm.
Morphology is assessed to determine the percentage of head and tail defects the sperm exhibit. A semen sample with less than 30% morphological defects is considered fertile. More tail defects can be tolerated than head defects because sperm with head defects will compete with normal sperm for fertilization of the egg.
It is important to remember that both hot and cold temperatures have the ability to affect bull fertility. Exposure to hot temperatures for more than eight hours will result in reduced motility and concentration of sperm produced. Cold temperatures also affect the concentration of sperm produced.
There is a two to four week delay before the effects of deleterious events such as heat stress, shipping, fever, or exposure to certain toxins can be observed by monitoring changes in the ejaculate characteristics. Six to twelve weeks are required before restoration of normal spermatogenesis can be accomplished after these events. To put this in perspective, if a bull experiences heat stress in July, you will not notice the effect until August and these effects can stick around until October. Conducting regular breeding soundness examinations will give you the knowledge you need to know about your bull's fertility.Schlesser is the Marathon County Extension agriculture agent