Contract-bred young Ultrablack bulls on the Barkly Tableland

OVER the past few months thousands of bulls have been sold to producers in every state.

These bulls are now moving into roles with new breeding teams. One of the challenges for any new bull is to find a place within the team and to undertake mating duties to his full capacity.

However, the impact of social structure within herds and among bull teams does play a significant part in determining how successful a new bull will be in achieving those duties.

While in more intensively-managed southern Australian herds, new bulls can be used in small teams or as single sires, northern Australian herds have greater challenges. The extensive and often harsh environment in this region, combined with the nature of multiple-sire mating systems commonly used, requires producers to understand how bulls interact within herds to maximise the investment they have made in new bulls this season.

The three areas of dominance, competition and mating behaviour directly affect reproductive success, impacting the overall calf output and herd productivity.

In multiple-sire herds, where two or more bulls are allowed to mate with a group of cows in a given paddock, dominance behaviour is a significant determinant of reproductive success.

Disparity

Geoff Fordyce

Dominance refers to the ability of a bull to control access to females in oestrus. In a paper published in FutureBeef discussing bull power, Dr Geoffry Fordyce highlights the fact that dominant bulls typically have higher mating success because they can establish territories near water sources or prime grazing areas, which increases their chances of encountering and mating with females.

These bulls often exhibit behaviours such as challenging other bulls, fighting, and patrolling, which reinforces their dominance over subordinates. Research conducted on northern Australian properties has shown that dominant bulls sire a significantly higher proportion of calves.

In herds where multiple bulls are present, approximately 14pc of bulls may sire more than 30pc of the calves, while up to 58pc of bulls sire less than 10pc​. This disparity in calf output underscores the importance of social hierarchy in determining reproductive success.

A bull’s dominance is influenced by several factors, including age, physical size, and temperament. Older bulls tend to be more dominant, as they have established themselves within the herd hierarchy over time. Bulls with larger body size and greater physical strength are more capable of defending their territory and access to females​.

Temperament also plays a role in dominance and mating success. Bulls that are more aggressive or confident tend to rise higher in the social hierarchy, giving them greater reproductive opportunities.

However, excessively aggressive bulls may be prone to injuries, largely because of their willingness to fight with other bulls.  This can see an impact in reduced fertility or incapacitate them during the breeding season.

It is important to recognise that dominance is not always related to the most favourable reproductive traits. Studies have shown that some dominant bulls may have poorer semen quality than subordinate bulls, but their behavioural traits and control over mating opportunities allow them to sire more calves​.

The size of the bull group within a herd can significantly affect individual calf output. In large bull groups (8 to 24 bulls), the maximum proportion of calves sired by an individual bull is typically around 26pc, with dominant bulls controlling a smaller share of the mating opportunities. However, in smaller bull groups (2 to 7 bulls), dominant individuals can sire up to 94pc of the calves​.

This dynamic suggests that smaller bull groups, combined with effective selection of dominant and fertile bulls, can lead to more predictable and concentrated calf output.

When fewer bulls are present, competition is reduced, and dominant bulls have more opportunities to mate without the constant threat of being displaced by challengers. However, the challenge with smaller groups is ensuring that all bulls can perform consistently, as fewer bulls mean each individual has a greater impact on reproductive success.

Timing of mating

The timing of mating within the breeding season also plays a role in calf output. Dominant bulls are often more effective early in the breeding season when females first come into oestrus. In extensive systems where cows are spread across large distances, the ability of dominant bulls to locate and mate with females during the peak oestrus periods is critical to achieving high conception rates.

As the breeding season progresses, subordinate bulls may have more opportunities to mate, particularly if dominant bulls become fatigued or injured from fighting​. This gradual shift in mating opportunities can help ensure that all cows are bred, but it may also lead to lower calf output if the subordinate bulls are less fertile or less aggressive in pursuing females.

In addition to dominance, behavioural traits such as libido, serving capacity, and sexual interest are key predictors of calf output.

Studies have demonstrated that bulls with higher libido and more frequent displays of sexual interest, such as mounting behaviour, tend to sire more calves. These traits can be measured through serving capacity tests, where bulls are observed in controlled mating environments to assess their sexual behaviour.

Bulls that perform well in these tests are more likely to be successful in multiple-sire herds, as they actively seek out mating opportunities. Conversely, bulls with lower libido or less aggressive mating behaviour may be outcompeted by more active bulls, leading to lower calf output.

Given the importance of dominance and behaviour in influencing calf output, effective management strategies are essential to optimise reproductive success in northern Australian herds.

One approach is to reduce the number of bulls used in multiple-sire herds while ensuring that each bull is fertile and has strong behavioural traits.

As noted by Geoffry Fordyce, once the ratio of bulls to cows exceeds 3.5pc, fighting and subsequent injuries increases significantly. Reducing numbers, provided all bulls have successfully passed a Bull Breeding Soundness Examination (BBSE), will ensure that smaller teams are as effective as possible as well as reducing the risks associated with fighting or with a less fertile but more dominant bull restricting mating opportunities.

By selecting bulls with strong behavioural traits, managing group sizes, and implementing sound breeding practices, producers can maximize calf output and improve overall herd productivity.

Click this link to read tonight’s second story on this topic: Traits that predict dominance in bulls – keys to understanding herd hierarchy

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