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Beef Breeder MANUAL
5.7.4. First Mating
Heifers should be bred at about 15 months of age to calve the following year as two year olds. Providing
that growth rates and condition score targets are met, calving heifers at two years of age is more proitable
than delaying calving until three years of age. Only heifers that have not met condition score and weight
targets should be considered for delayed mating if it is not economical to supplementary feed them to achieve
the targets. Cattle have an oestrus cycle about 21 days in length.
Mating heifers for six weeks 42 days permits each heifer to be exposed to the bull during two successive cycles,
during which it is expected most fertile individuals will become pregnant. A six-week mating period also
ensures that greater management control of the heifers can be exerted, including;
• Ensuring that the nutritional needs of the heifers are met
• A reduced period of intense supervision of calving is required
• Weaning and marking can be carried out at the same time for the entire drop of calves
• Replacement heifers can be mated as a group as they will reach target weights and condition score at
a similar time when well managed. However, if the enterprise is in a herd build-up phase,
where increasing the total number of breeders is desirable, an extended joining period to three oestrus
cycles 63 days will increase the total number of calves subsequently born, but these later-calving heifers will
likely have lower rates of pregnancy when joined a second time as their period of recovery between calving
and being expected to conceive again is reduced. Some beef enterprise managers join heifers a month
before the main herd to allow greater supervision of the heifers at calving, and provide them with an extra
month to regain body condition in readiness for the next breeding cycle.
However, in an environment with a deined window of ideal weather such as Russia, calving heifers a month
earlier when extreme cold weather is still a risk is not recommended unless the enterprise operators have
considerable experience in managing calving at this time.
5.7.5. Selecting Appropriate Sires for Heifer Mating
Bulls selected for use with heifers must have characteristics that favour easy birth of their ofspring,
such as narrow shoulders and smooth body conformation. Where possible avoid sires known to
sire high birthweight calves andor display a broad shouldered phenotype that may contribute to dystocia.
Additionally, if rapid genetic improvement of the breeding herd is desired, use of superior performance
bulls with heifers the most genetically advanced generation in a breeding herd is desirable if such
performance information is available.
Young bulls up to three years old are usually physically smaller and lighter than when mature from four years
of age and are less likely to injure heifers during mating.
Artiicial insemination AI is an alternative breeding strategy that, when well-managed, eliminates the risk
of injury to the heifer during mating and allows easy access to leading genetics in the breed. However, AI
has signiicantly lower conception rates than natural mating and this needs to be carefully considered before
embarking on an artiicial breeding program.
Care must be taken to ensure older bulls or AI sires used for several years are not mated to their own daughters
when selecting sires to use with heifers. If heifers are irst calved at two years of age, a bull in his third mating
season will likely have sired some of the heifers being joined for the irst time that year. Mating closely related
animals decreases herd productivity and should be avoided. Consequently, sires for use with heifers need
changing at least every second year.
5.7.6. First Calving
By the time they calve, heifers should weigh at least 440kg or about 80 of their expected mature body weight, and
be in BCS 3.0 to 3.5. If these targets are achieved, the heifers will have less problems calving, as their body size
will more easily cope with the delivery of the calf.
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Cold Winter Climates
This is further helped by the use of bulls selected specially for use with heifers, and which produce lower
birth weight calves. Heifers that calve early in the calving period are also less likely to have dystocia issues as the
shorter gestation period tends to reduce the size of the calf.
First calving heifers must be fed suiciently well to ensure that they milk well and support good calf growth, but
also to enable the mother to continue their own growth and development. This involves feeding to at least a level
that enables the heifer to maintain liveweight during the lactation period, and particularly between calving and re-
mating to ensure that she resumes cycling quickly, and is able to achieve a second pregnancy in the shortest
timeframe. If heifers are not achieving target condition scores
they must be relocated to better quality and quantity of pasture, supplementary feed, or the calves weaned
early.
5.8. Relationship Between Feeding
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