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Improving female herds’ fertility
by using DTC EBVs
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By: IZAAN DU PLOOY: Technical Officer at the LRF
Reproduction is one of the key drivers of profitability in
any beef cattle farming enterprise. Without a thriving calf
on the ground, no product will be available for sale.
Fertility and reproduction should thus be the focal point of
a beef farmer’s decision-making process.
Reproduction is
one of the key drivers of profitability in any beef cattle
farming enterprise. Without a thriving calf on the ground,
no product will be available for sale. Fertility and
reproduction should thus be the focal point of a beef
farmer’s decision-making process.
does not do this; she is costing the farming
operation money and therefore decreasing the profitability
of the operation.
While many
producers manage the reproductive performance of their
female herd using different management
strategies, in particular the
culling of females that fail to conceive, research has shown
that female fertility is influenced by the genetics of the
breeding herd.
The question is thus, how does a beef breeder select for
improved fertility?
Available female fertility selection tools
Days to Calving (DTC)
is the female fertility trait that BREEDPLAN uses to
identify females that are genetically more fertile. DTC is
the time from the start of the joining period (i.e., when
the female is introduced to a bull) until subsequent
calving. As gestation length is constant, the main variation
in days to calving is due to differences in the time taken
for females to conceive after the start of the mating
period.
DTC is preferred over ICP as an indicator of female
fertility. The main reason for this is that with ICP, there
is a voluntary waiting period regarding when the bull is put
with the cows. The breeder decides when he puts the bull or
bulls with the cows. He can, for example, delay the start of
the breeding season, which will increase a cow’s ICP. This
increase is due to environmental factors rather than changes
in her genetics. This extra environmental noise makes it
more difficult to identify the genetic differences between
female animals with regard to fertility. Delaying the start
of the breeding season will not affect a female’s Days to
Calving.
Furthermore, when you only have consecutive calving dates
(which is used to calculate ICP), it is difficult to know
which cows were treated the same, mated together, and
therefore had the same opportunity to conceive. When the
mating information is available, you know which cows were
exposed to a bull and which were not. It is thus also easier
to identify non-calvers.
The Days to Calving EBV promotes cows that calve earlier in
the season compared to those that calve later, while
penalising cows that do not calve.
Why does it make sense to select for females conceiving
early in the mating season?
The aim of any beef cattle operation should be to
produce at least one calf per breeding female per year.
If the average gestation length of beef cows is about 283
days (depending on the breed, sex of the calf, etc.), there
are about 82 days (365 – 283) left for a cow to recover and
reconceive after giving birth. The postpartum anestrous
period in beef cattle varies from 45 – 90 days. There is
thus a very small window period for a cow to reconceive to
ensure that she calves down again within 365 days.
Scenario:
Every year, on the 1st of January, you put the bulls with
the cows for three months, and you take them out again on
the 31st of March. The mating period is thus 90 days. The
first possible date for the calves to be born is around the
10th of October.
Cows that calved on the 10th of October have 83 days to the
start of the next breeding season and thus have enough time
to recover and start cycling again. The last possible date
for calves to be born is around the 8th of January. Then the
next breeding season has already started. These cows will
need to recover and reconceive in a very short period;
otherwise, they will still be open at the end of the mating
season and will not produce a calf within 365 days.
There is thus a good argument for selecting those cows that
conceive early in the breeding season and therefore calve
early in the breeding season, as they will have enough time
to recover after calving and be ready to reconceive early in
the next breeding season. Furthermore, a calf born earlier
in the calving season is likely to be heavier at weaning as
it has had more time to grow up until weaning.
What information should be recorded:
As Days to Calving is calculated from when the females are
first exposed to the bull or bulls, the recording of mating
information is thus very important.
Breeders should record all ‘events’ associated with the
joining of their females from the start of the mating period
in each breeding season through to when the subsequent
calves are born.
Broadly, the information to be collected should include:
●
Mating details (bull in dates) of all females (heifers and
cows) mated within the herd.
●
Details of all females removed from the herd, particularly
those present at joining that were no longer with the herd
by the time of the subsequent calving.
●
Details of all calves (dead or alive) that are born because
of these matings.
Please note that, currently, the Days to Calving analysis
will only utilise information for females that have only
been naturally mated within the breeding season (i.e., they
have not also been included in artificial insemination (AI)
and/or embryo transfer (ET) programs, or artificially
induced to cycle before joining with the bull outside of
such programs). However, research is underway to utilise AI
records. Breeders who undertake such programs followed by a
natural “backup” mating are strongly encouraged to submit
details of their AI programs to assist in this research.
Understanding Days to Calving EBVs:
Days to Calving EBVs are estimates of genetic differences
between animals in the time from the start of the joining
period (i.e., when the female is introduced to a bull) until
subsequent calving. Days to Calving EBVs are expressed in
days.
Lower, or more negative, Days to Calving EBVs are generally
more favourable. For example, a bull with a Days to Calving
EBV of -5 days would be expected to produce daughters that
conceive earlier in the joining period than the daughters of
a bull with a Days to Calving EBV of +5 days. Females with
shorter Days to Calving EBVs also tend to be those that show
early puberty as heifers and return to oestrous earlier
after calving.
Days to Calving EBVs thus provide a useful tool that
breeders can use to improve the genetics of their females
for fertility, in conjunction with their routine management
and culling strategies.
How to submit Days to Calving information:
There are two different methods available to submit the
joining details and Days to Calving disposal codes to the
society:
●
A BREEDPLAN compatible herd recording computer program, such
as HerdMASTER.
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The BREEDPLAN compatible Microsoft Excel templates
(available to download from the Limousin website). Several
templates are available and are described below:
1. Submitting DTC Information - Natural & AI Joinings.
For providing natural joining and/or AI program information
to BREEDPLAN. Often submitted upon completion of joining.
2. Submitting DTC Information – ET Programs.
For providing ET program information to BREEDPLAN. Often
submitted upon completion of joining.
3. Submitting DTC Information - Preg Test Results.
For providing pregnancy test results. Often submitted
at completion
of pregnancy testing.
4. Submitting DTC Information - DTC Disposal Codes.
For providing DTC Disposal Codes for any female that left
the herd between joining and calving. Often submitted at
completion of pregnancy testing and/ or subsequent calving.
Sources:
BREEDPLAN tipsheets: Understanding Days to Calving EBVs &
Recording Days to Calving Information.
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