September is such a busy time on most dairy farms, calving is coming to an end, spring forage harvesting is (hopefully) getting into full swing and one of the furthest things from a farmer’s mind is preparing the bull team for the upcoming mating period if you plan to use bulls in your breeding program.
As dairy farmers, we put enormous time, money and energy into ensuring each breeding season is a success, carefully planning mating programs, managing cow nutrition, and scheduling joining dates to align with the herd goals.
Yet, one critical step is sometimes overlooked — procuring and testing bulls well before the breeding season begins.
Whether you run a natural service program or use bulls alongside artificial insemination, pre-breeding bull checks can mean the difference between a compact calving period and an extended, costly one.
No farmer should ever ‘test’ their bulls’ fertility by taking a chance with their entire livelihood.
The primary reason to test bulls before breeding is simple: fertility is not guaranteed.
Even the best looking bulls can have reproductive issues that won’t show up until we find that the cows are left empty months later.
Common causes of subfertility or infertility in bulls include low sperm count or poor semen motility, physical injuries to legs or feet that affect serving ability, testicular abnormalities or infections, age-related decline in fertility or previous illness or high fevers that may temporarily reduce semen quality.
A bull’s fertility can change from year to year — and sometimes even within the same season — so relying on past performance is risky at best.
Most veterinarians recommend a Bull Breeding Soundness Examination (BBSE) six to eight weeks before joining, allowing for any problems to be addressed and for replacement bulls to be sourced if needed.
The breeding soundness exam is not just a crush-side assessment of a semen sample — it also includes a thorough physical examination, palpation of the reproductive tract and appropriate measurements, and I also strongly recommend that semen morphology is assessed.
Semen morphology is assessed in the laboratory under high-powered microscopes looking at more than 200 individual spermatozoa to check for developmental abnormalities.
This is important because some semen defects do not necessarily affect the sperm’s ability to swim to the egg, but any resulting fertilisation will not result in a viable pregnancy.
So, a bull with a high percentage of mobile but abnormal sperm can dramatically increase the risk of an unsuccessful mating because if the sperm that penetrated the egg first is abnormal, that cow will return in three weeks’ time and can result in late calving animals who fall out of the desirable ‘high fertility cycle’.
The high fertility cycle is simple.
Early calving animals have calves that are older and likely better grown at their own first joining so they also become early calving heifers.
An early calving animal has longer to recover after calving before mating start date and therefore has a lifelong advantage.
Empty cows are expensive, not just this year but for years to come. When subfertile bulls are put with a mob, it may result in a higher number of late-calving or empty cows.
If using multiple bulls, it’s worth testing them all.
A single infertile dominant bull can suppress the activity of the other more fertile bulls, leading to poor conception rates. Ensuring bulls are a similar size, age and temperament can reduce this risk.
I absolutely love when a client contacts me early and asks me what steps they should be taking to ensure their bulls are in tip-top form rather than it being a huge rush at the end and bulls are not correctly managed, exposing a herd to unnecessary risks.
If there is plenty of time, not only can we ensure that the bulls are fertility tested prior to use but we can also ensure that they are ear notch tested for BVDV (pestivirus) and fully vaccinated against diseases like vibriosis, botulism, BVDV and up-to-date with 7-in-1 vaccines so they are less likely to succumb to, or spread diseases.
I strongly advise my clients against leasing bulls or buying aged bulls that have been used previously in other herds as it is just good biosecurity.
There are a lot of herds that I work with who tell me that they are a closed herd, having not bought any cows for years, yet they buy a handful of bulls each year.
Testing bulls before the breeding season is one of the most cost-effective insurance policies you can take out for your dairy herd.
A single infertile or subfertile bull can cause ripple effects that last for years in your calving pattern and bottom line.
By contacting your vet and investing in a BBSE and proactively managing your bull team’s health, you give your herd the best chance for a tight calving pattern, strong milk production and long-term profitability.
Dr Rob Bonanno is a ProDairy lead veterinarian based in Gippsland.