Genetics

Traits that predict dominance in bulls – keys to understanding herd hierarchy

Genetics editor Alastair Rayner 10/09/2024

IN cattle production, particularly in multiple-sire herds, dominance among bulls significantly influences reproductive outcomes and herd dynamics.

As noted in tonight’s weekly genetics review, dominance dictates which bulls have the greatest access to females, affecting calf output, mating success, and overall herd productivity.

While dominance is often established through direct competition and social interactions, several key traits consistently predict which bulls will rise to the top of the hierarchy.

Understanding these traits can help cattle producers select and manage bulls more effectively, reducing conflicts and optimising reproductive success.

Age and physical size are among the most important predictors of dominance in bulls. Older bulls tend to dominate younger ones because of their experience, established roles within the herd, and greater physical maturity.

Older bulls are both larger and stronger, making them better equipped to defend their access to females. Size, in particular, correlates strongly with dominance, as larger bulls are often better able to win fights and hold territory within the herd​.

Studies conducted on cattle herds in northern Australia show that dominant bulls often control a significant portion of the mating opportunities. In multiple-sire herds, a dominant bull can sire a disproportionate number of calves, sometimes accounting for more than 30 percent of the total offspring.

Size and physical power play a central role in their ability to fend off rivals and secure these reproductive advantages.

Beyond age and size, muscle mass and general physical fitness are critical components of dominance. Bulls in prime physical condition are not only more capable of competing with other males but are also more attractive to females.

Strong, well-muscled bulls are better able to withstand the physical demands of competition, which often involves head-butting, charging, and physical combat during the breeding season​.

Maintaining bulls in peak physical condition through proper nutrition and health care is essential for ensuring that they can effectively assert dominance when necessary. Bulls that are under-nourished or fatigued may lose their dominant status to more physically fit rivals, resulting in reduced mating opportunities.

Aggression, temperament

One of the strongest predictors of dominance is a bull’s aggression and temperament.

Bulls that exhibit higher levels of aggression are often more dominant because they are more willing to engage in direct physical confrontation with rivals. Assertive bulls are more likely to win fights and establish control over territories where oestrous females are present​.

However, aggression needs to be balanced with social intelligence. Bulls that are overly aggressive may injure themselves or others, reducing their ability to mate.

In contrast, bulls with a balanced temperament – confident and assertive without being reckless – tend to maintain their dominance more effectively over time. These bulls are often more successful in large herds, where maintaining social order and avoiding injury are critical for long-term reproductive success​.

While physical strength and aggression are critical, social intelligence – the ability to navigate herd dynamics and understand social cues – also plays a role in predicting dominance.

Bulls with more experience in the herd are often more dominant because they have learned how to assert control without constant physical confrontation. These bulls understand when to engage in fights and when to use social signals to maintain their status​.

Real estate

Experienced bulls often occupy the most desirable territories, such as areas near water or food sources, where females are more likely to congregate. By holding these prime positions, they increase their chances of mating with oestrous females without needing to engage in constant physical battles.

Libido, or sexual drive, is another significant predictor of dominance. Bulls with higher libido are more active in seeking out oestrous females and engaging in mating behaviour.

This increased sexual activity often translates into greater reproductive success, as these bulls are more likely to be present during peak mating periods and less likely to miss opportunities to mate. ​In multiple-sire herds, bulls with high libido may outcompete others for access to females, further reinforcing their dominant status​.

Inheriting Dominance?

There is evidence that certain aspects of dominance, such as libido, fertility, and even temperament, have a genetic basis.

Bulls from genetic lines known for strong reproductive traits are more likely to exhibit dominance within the herd. Scrotal circumference, for example, is a heritable trait linked to fertility and reproductive success. Bulls with larger scrotal circumferences often produce more sperm, which correlates with higher reproductive success and can enhance their dominance​.

Genetic selection programs that prioritise reproductive traits can help cattle producers select bulls with a higher likelihood of becoming dominant. By choosing bulls from lines with proven fertility and strong behavioural traits, producers can improve herd reproductive performance and reduce the need for constant bull replacement.

Dominance in bulls is a multi-faceted trait influenced by physical, behavioural, and genetic factors. Age, size, muscle mass, aggression, libido, and social intelligence all play critical roles in determining which bulls will rise to the top of the hierarchy in multiple-sire herds.

By understanding and managing these traits, cattle producers can select bulls that not only contribute to higher reproductive success, but also maintain the balance of power within the herd, reducing injuries and optimising productivity.

Effective bull management involves balancing these dominant traits with sound health care, regular fertility evaluations, and strategic herd management practices to ensure long-term success in breeding programs.

 

Click this link to read tonight’s second story on this topic: What are the dominant bulls doing in your herd?

 

Alastair Rayner is the General Manager of Extension & Operations with Cibo Labs and Principal of RaynerAg.  Alastair has over 28 years’ experience advising beef producers & graziers across Australia.   He can be contacted here or through his website www.raynerag.com.au

 

 

 

 

 

 

 

 

 

 

 

 

 

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