The importance of bull fertility is easily under appreciated. In the table below it illustrates how a 20% difference in fertility can have a huge impact.
Assumptions:
Any cow not pregnant is replaced and is able to be breed during the first heat cycle. (no costs were include to replace open cows)
71 % of cow will move up one cycle and be available to be bred the following year. This is based on and average of 54 days for uterine involution and recovery.
The purpose of this table is for illustration only. However, it does show the importance of important aspects of the bull breeding soundness exam, especially of sperm morphology. You would not expect a bull with a 60% normal morphology to perform as well and one with an 80% normal morphology. The costs to the cow-calf producer is often hidden but quite substantial.
Notice that even with a 60% effective rate the final pregnancy rates continue to be 90% and over. Few producers would recognize the potential losses being given up do to a slightly sub-fertile bull.