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Most spring calving farms, particularly those in the southern half of the country have completed six weeks of AI. Six weeks of AI and six weeks of natural service with bulls is the traditional approach to breeding.
However, just because the bulls are out does not mean the breeding season is over. In fact, the second six-week period is often a higher risk period for problems compared to the first six-week period.
Every year we hear of problems with bulls causing higher than normal empty rates, or delayed calving interval.
Bull infertility brought on by lameness, disease or stress is a common problem. In many cases this infertility is transient, as the bull can start off OK, but go infertile or sub-fertile for periods.
The highest risk of a sub-fertile bull causing a problem is where only one bull is being used. All the workload is on that bull so if something goes wrong with him, cows that come in heat during the period he is infertile will not go in-calf.
The bull doesn’t have to be infertile for there to be problems though. Sometimes, young bulls take a week or so to get the hang of it.
Even older bulls can often take time to adjust to life as a stud. Effectively, these bulls have been starved of sexual activity for the last 11 months, so they can be a bit too eager when they get the chance.
Best policy is to continue with AI for a week or 10 days after the bull is let out. Use more than one bull to reduce the risks of infertility or sub-fertility affecting breeding performance.
Keep an eye on the bull’s activities. During a mount, check that his rod is normal and he is able to serve the cow.
Record the numbers of the cows that he is serving and check, in three weeks’ time that the cows are not coming around bulling again.
Remember that bulls are dangerous and even ‘quiet’ bulls can turn cross and pose a risk. Always have an escape plan in mind when moving bulls. If bulls turn dangerous, remove and replace them.
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