Beef Cattle Semen Fertility

Beef Cattle Semen Fertility from Artificial Insemination Sires

     Is there a variation in fertility of semen from artificial insemination (AI) sires?

     Have you ever suspected that semen from some bulls gets cows pregnant more often than semen from some other bulls? Could this be a beef cattle semen fertility issue?

     Do conception rates for a specific AI sire tend to be similar over time?

     Sometimes an AI bull gets a reputation as having poor semen fertility. Have you ever considered if this lack of beef cattle semen fertility reputation is deserved? 

Why is semen fertility important?
     Semen fertility is important because poor fertility semen requires more services to get a cow pregnant and this results in increased days open and subsequent calving intervals. In addition, semen with poor fertility requires more units of semen to result in a pregnancy and a subsequent calf. Both of these impacts are economically important to producers and, as a consequence, semen from sires with poor fertility is not nearly as good of an investment as semen from high fertility sires (assuming other genetic evaluations are similar).

     In some countries information on semen fertility is available on most AI sires that have been used heavily as service sires. In the US, the widely accepted measure of AI semen fertility is called Expected Relative Conception Rate or ERCR. Each individual bull has an ERCR and this ERCR is calculated much like we calculate genetic evaluations for production traits or other traits. These ERCRs are made available on bulls once they have been used for a significant number of recorded services and we have information on the outcome of these services.

     However, these ERCRs have a slightly different interpretation and use compared to other routine genetic evaluations.

     Breeding companies work diligently to ensure that AI semen is of the highest quality possible.

     Breeding companies continually monitor semen quality from each sire and work to optimize semen processing for specific sires. In some situations, breeding companies include higher sperm numbers per straw for some bulls in an attempt to increase the conception rate to a reasonable level. One of the most important things that breeding companies do to ensure the best semen quality is to eliminate bulls from their programs that are not good semen producers or who produce very poor quality semen. You can be assured that semen from the major breeding companies around the world is as good as possible given current technologies. However, breeding companies do not currently have the technology to make the fertility of semen from all AI bulls equal. As a consequence, it is true that semen from some AI sires is more fertile than semen from other AI sires.

     Large differences in fertility among AI sires are rare because of the efforts of the breeding companies, but AI sires can differ by several percent in conception rate. Some of the poorest bulls for conception may produce semen that has a conception rate of 5% to 10% lower than some of the best bulls for conception. For example, you might expect a first service conception rate for an outstanding bull to be 40% in a specific herd and a first service conception rate of 30% for very poor bull when used in the same herd. In this example herd, most bulls would be expected to have conception rates close to 35% but there would be variability among the other bulls as well.

     Research data from several studies in several countries indicates that AI sire fertility tends to be similar for specific bulls across time. Bulls that have had poor fertility in the past will very likely have poor fertility in the future. This means that semen fertility is very repeatable over time and this allows geneticists to use past data to predict future semen fertility. As a result, we can have confidence in the measures of semen fertility over time.

     What else might these semen fertility measures on AI sires tell us? Does semen fertility for a sire tell us much about what to expect for fertility of semen from his sons? Perhaps more important, does semen fertility tell us anything about the expected fertility of a sire's daughters?

     The answer to both questions, unfortunately, is that the semen fertility from an AI sire is not a very good predictor of his sons' fertility or his daughters' fertility. There are no studies in dairy cattle that have indicated a close association between semen fertility for a sire and the fertility of his daughters. Somewhat contrary to these results in dairy cattle, research results in beef cattle and swine do indicate that male scrotal measurements are useful for predicting female offspring reproductive performance.

     It is clear that, despite the best efforts of breeding companies, semen from AI sires do vary somewhat in fertility. This variability is predictable over time and poor fertility AI sires identified from past data will more likely have poor fertility in the future.

     Fortunately this variability in semen fertility is moderated by the work of the breeding companies so producers can expect reasonable conception rates from AI bulls marketed by reputable breeding companies.

     However, fertility of semen from AI bulls should be considered when making semen investment decisions.