Are your bulls sound?
Bulls can fail to mate successfully for many different reasons. They can have libido issues, back and feet problems, penile defects and poor quality sperm, all of which can lead to reduced pregnancy rates in beef and dairy herds. Many of the defects seen can be acquired, so just because a bull worked well last season and got his cows in calf, it doesn't necessary follow that he will do the same again.
There are several different ways to evaluate a bull's fertility. They all have their relative merits but at Totally Vets, we believe the most effective and comprehensive method is to collect semen from the bull using an artificial vagina (AV) while a cow or heifer in a bale is mounted. By using this method, adopted from Robyn How from Tararua Breeding Services, all the aspects of bull fertility mentioned above can be evaluated.
This may sound like a big issue to carry out but all that you need is a decent set of yards and a cow or heifer that is preferably on heat ( but not essential). We have a portable bale to put the heifer or cow in that we can fit just about anywhere. We can test from a single bull up to fifty or more in one session and can get through in the region of 20 per hour if they are working well. The efficiency of the testing can be improved considerably with some preparatory work on the bulls beforehand.
The other methods commonly used to evaluate bulls are the Blockey test and electro-ejaculation. With the Blockey test, a semen sample is not collected for evaluation; when testing large numbers of bulls, a heifer or cow is served many times which can have welfare implications for the heifer if not closely monitored. The Blockey test is weighted heavily towards libido and requires multiple serves by a bull in a given time frame. With electro-ejaculation, the penis is often not seen and a bull's libido and ability to mount are not evaluated.
Since we have been using our preferred method of evaluation,c ollecting with an AV, we have identified a few issues that would almost certainly have been missed if one of the other methods had been used. This was recently highlighted when we were asked to investigate a high empty rate in some beef cows. Of five bulls that had previously passed a Blockey test (i.e. demonstrated an ability to mount and serve) three had very poor semen when collected with an AV and evaluated. This poor semen was almost certainly the cause of the fertility issue.
No method of evaluation is perfect but Totally Vets and Tararua Breeding Services believe that the method we have adopted as our standard is the most comprehensive and welfare-friendly testing available. Please give us a call if you would like to find out more.
