Measure, Don’t Assume: Dr Ced Wise Highlights the Importance of Wagyu Bull Fertility at WagyuEdge’26
Wagyu’s reputation for exceptional fertility is well deserved, but producers should never take it for granted.
That was the key message from renowned cattle reproduction specialist Dr Ced Wise, who delivered an engaging and highly informative presentation on bull fertility at WagyuEdge’26 in Brisbane, challenging breeders to look beyond assumptions and place greater emphasis on measurement, monitoring and management.
Speaking to a packed audience of Wagyu producers, Dr Wise explored the science behind sperm production, testicular function, puberty and fertility assessment, while highlighting why bull fertility remains one of the most important drivers of herd productivity.
Fertile by Nature – But Not Immune to Problems
Dr Wise acknowledged that Wagyu cattle are widely recognised for their fertility and their ability to reach puberty earlier than many other breeds, traits that have contributed significantly to the breed’s expansion across diverse production systems throughout Australia.
However, he warned against assuming every Wagyu bull will automatically be highly fertile.
“Fertility spans the spectrum from sterile through subfertile to highly fertile,” Dr Wise explained, noting that even a single subfertile sire can have significant impacts on joining outcomes, particularly in single-sire mating systems.
His central message was simple: measurement matters.
“Please measure, don’t just assume,” he urged producers. “We do not want to lose that ability or that reputation for being highly fertile. It is a big part of the Wagyu breed.”
Understanding the Biology Behind Fertility
A large part of the presentation focused on the biology of sperm production and the remarkable complexity of the bull reproductive system. Dr Wise outlined how healthy sperm production relies on a combination of spermatogenesis, hormonal regulation, sperm maturation, transport and effective thermoregulation.
One of the most important factors is temperature control.
Bull testes must remain between two and six degrees Celsius below body temperature to maximise production of normal, motile sperm cells. A sophisticated cooling system involving blood vessels, specialised anatomy and the scrotum itself works continuously to maintain this temperature balance.
When that system is disrupted, fertility can suffer.
Heat stress, illness, inflammation, injury and even prolonged periods of inactivity can elevate testicular temperature and reduce sperm quality. The effects may not appear immediately and can persist for weeks or months after the initial insult.
Dr Wise explained that severe fertility setbacks can take more than 70 days to fully recover because of the time required to produce a new generation of sperm from the earliest stages of development.
Why Management Matters
Beyond heat stress, Dr Wise highlighted a range of everyday management factors that can influence fertility.
Physical trauma from fighting, transport stress, poor nutrition, mixing unfamiliar bulls and social hierarchy disputes can all negatively affect reproductive performance by disrupting testosterone production and sperm development.
Nutritional management was identified as a particularly important tool for breeders aiming to maximise reproductive performance.
Research has shown that feeding high-energy diets to young bulls before puberty can decrease the age at which puberty is reached, increase testicular size, improve daily sperm production and raise testosterone levels. Conversely, nutritional restriction can delay sexual development and reduce fertility potential.
Measuring Fertility
Dr Wise outlined the three primary tools currently used to assess bull reproductive performance:
- Scrotal circumference
- Sperm motility
- Sperm morphology
Scrotal circumference remains one of the most practical and useful indicators because it is strongly correlated with testicular weight, sperm production and age at puberty. It is also moderately to highly heritable, making it a valuable selection tool.
However, Dr Wise noted that Wagyu bulls continue to challenge industry assumptions.
While many breeds reach puberty at around 28 centimetres scrotal circumference, Wagyu bulls often demonstrate fertility at measurements that would be considered pre-pubertal in other breeds. Exactly why this occurs remains unclear.
“We know Wagyu can be fertile at circumferences that would be pre-pubertal in most other breeds,” he said. “What is the minimum scrotal circumference in a Wagyu? I don’t think any of us know for sure yet.”
Unanswered Questions About Wagyu Fertility
Throughout the presentation, Dr Wise repeatedly pointed to opportunities for further research.
He suggested several possible explanations for Wagyu’s fertility advantage, including higher sperm production per gram of testicular tissue, lower rates of cell loss during sperm development, or structural differences within the testes themselves.
He also raised the possibility that Wagyu may possess anatomical features that improve their ability to regulate testicular temperature, potentially helping explain their strong reproductive performance in northern Australian environments.
“We need more research in that area,” he said, particularly as Wagyu populations continue to expand into warmer production regions.
Balancing Genetic Progress with Reproductive Performance
Dr Wise concluded by discussing the growing pressure placed on young sires as genomic technologies continue to accelerate genetic gain and shorten generation intervals.
As elite bulls are identified at increasingly younger ages, producers and semen collection centres are being challenged to collect high-quality, freezable semen from animals that may not yet have reached full sexual maturity.
While genomic technologies offer enormous opportunities, Dr Wise reminded breeders that fertility must remain a core consideration alongside selection for performance and carcase quality.
“Wagyu are rightly renowned for their meat quality and their fertility,” he said. “But focusing only on selection for efficient production of the highest quality meat and assuming they will always be fertile is misguided.”
For Wagyu breeders, the message from WagyuEdge’26 was clear: fertility remains one of the breed’s greatest strengths, but maintaining that advantage will require ongoing measurement, sound management and continued investment in research.