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Beef Breeder MANUAL
Sperm quality can vary from one test to another, even in healthy bulls. Nutrition, temperature, illness, time since
last ejaculation, bull age, and the proiciency of semen collection can all inluence the results of a semen
quality test. Bulls with low semen quality results should be tested a second time at a later date before being
permanently excluded from the breeding program.
5.3.7. Ability to Mate Serving Capacity
A bull must have both the physical ability and the desire to mate with cows in order to be useful in a breeding
program. All bulls being considered for use must demonstrate the ability to mount, position themselves,
direct their penis into the cow, and ejaculate. Observing a bull while in the company of a cycling cow will quickly
reveal if he has any basic interest in mating, and whether he is capable of successfully mating.
Most bulls naturally exhibit a strong desire to mate with cows that are cycling, so it is usually the ability to
mate that is of most importance in a serving capacity test. The most common problem likely to be observed
is failure to align the penis with the vagina. Deviation ‘corkscrewing’ of the penis, or a loose, swinging sheath
may make alignment diicult, and bulls with these characteristics should not be considered for use in a
breeding program.
5.3.8. Bull Management and Preparation for Mating
Bulls should be assessed for general health and body condition score BCS at least two months prior to
joining. Ideally bulls should be a BCS of 3.0 to 3.5 during mating so provision of adequate nutrition in the months
prior to joining is essential to achieve this. Over-fat bulls above condition score four are prone to heat stress,
which can impact on fertility. Supplementary protein in the diet leading up to mating will improve testicular
development and sperm production.
Bulls intended for use in the same mob should be put together if not already at least two months prior to
joining to allow social hierarchy to be established before mating begins. This reduces the chances of ighting and
injury during the joining period.
During the joining period, bulls should be observed weekly to ensure they are actively working and are not
injured. Bulls should also be vaccinated annually against diseases that afect reproduction Refer Section 4.5.3.
When managed correctly, bulls may be used for breeding as yearlings. Yearling bulls are capable of successfully
breeding with heifers and adult cows, provided they are suiciently grown and meet the minimum bull
evaluation criteria. Yearling bulls can be used in multi- bull groups, but only with other yearlings. Mixing them
with older, bigger bulls increases their risk of injury during the joining period. Once they have been removed
from a mating group, young bulls should receive highly nutritious feed to help them regain body condition and
to continue their growth and development.
5.3.9. Bull to Cow Ratio
Bulls should be joined with 30 to 50 cows each, with 40 being the optimum number. Joining bulls to less
than 30 cows is an ineicient use of bulls and increases overall bull purchase costs. In multi-bull herds with less
than 30 cows per bull, increased competition for the few receptive females also often results in ighting and
injury to both bulls and cows. Single sire mating reduces bull injuries from ighting, but increases the potential for
poor conception rates if the bull becomes infertile or incapable of mating through injury or illness.
Young yearling bulls should not be joined with more than 30 cows each.
Reserve bulls are essential to replace any of the main working bulls that are injured or otherwise unable to
mate as soon as they have been identiied. A guide to the number of reserve bulls required is about 10 to 20
of the number of working bulls, with the cost of having extra bulls being compared with the risk of production
losses, if not enough reserve bulls were available when required.
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Cold Winter Climates
5.4. Cows
