Angus Australia



The management of bulls has a large impact on herd reproduction. Bulls with low fertility lead to low pregnancy rates and/or increased calving spans. This ultimately leads to reduced throughput of weaners and animals meeting market specifications, and consequently reduced enterprise profits.

During joining, pay special attention to 1st year joining bulls. Observe the bull to make sure he is fit, able and working well. Check 3–4 times/week during joining and more frequently during the first cycle of joining. If a bull does break down or is suspect, remove, treat or replace if needed so as to cause minimal disruption to your joining program.[14]

Joining heifers

How a heifer calves in her first gestation, in relation to the calving span of the herd, determines the relationship for the rest of her life. Heifers that calve early in the calving season will continue to do so for the rest of their life.[21] It is therefore important to join bulls of highest serving capacity to heifers so the heifers have the highest chance of getting in-calf at their first joining. If they calve early in the first season they tend to be early calvers for the rest of their lives.[12]


Joining heifers a month earlier than the main herd is a management option that enables the heifers more time after calving to begin cycling before the start of mating.[22]

Ensure bulls of similar age are used together and that bulls spend their time serving cows rather than fighting.[14]

How many bulls?

Carefully consider the number of bulls allocated to mating groups or herds. Insufficient bulls for the number of cows in a herd may result in:[18]

  • lower pregnancy rates
  • reduced throughput of animals meeting market specifications

Having too few bulls can present a risk if a bull becomes infertile during the mating season.[7]

Too many bulls can also present a risk and may result in an increase in fighting amongst bulls and reduced fertility due to injury.[7]

Calculate the number of bulls required for joining, a minimum of 2 bulls per 100 cows or per herd (variable depending on terrain).[18]

  • Retain 1 in 10 of total bulls in reserve so that injured bulls can be replaced as soon as they are identified


Plan mating groups eight weeks before joining to ensure bulls are run together before mating so they can establish their social groups.[20]

Mating load, or bull power will vary with bull breed, size, age, testicular size and management factors.