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The maternal female - What
makes a good cow?
____________________________________________________
Source:
www.breedplan.une.edu.au/extension-services/resources/use-of-resources
A female plays an important role in the herd. Not only does
she contribute 50% of her genetics to her calf, but she is
also required to get pregnant, give birth, wean her calf,
and get back in calf, all while maintaining her own
condition at an acceptable level. This article will examine
the traits that make a good maternal female and explore how
genetics can help to improve compliance levels within the
herd for each of these important life stages.
THE MATERNAL FEMALE
The job of a female (whether a maiden heifer or an older
cow) in the breeding herd is to:
1. Get in calf (in the first or second cycle) and carry the
calf to term.
2. Give birth to a live calf (without assistance).
3. Wean the
calf.
4. Get back in
calf, thus repeating the cycle in the next year.
In addition,
she should do all of this without consuming excessive
amounts of feed (in turn improving the stocking rate
for the property and thus giving
producers the option to run more animals).
While beef producers will often cull cows from the herd that
do not perform at each step, simply removing the individual
cow does not remove the underlying poor genetics from within
the herd (as the parents and/or progeny are not culled).
Without making genetic improvement within the herd to
improve compliance levels at each step, the problems will
simply repeat themselves in subsequent calving drops.
A
classic example of this is seen in the change in docility in
Australian Limousin. While breeders were culling animals
with poor temperaments from each calving drop. It wasn’t
until the Docility EBV was introduced that breeders were
able to make informed decisions about which sires and dams
to select (previously, poor temperament was passed on
because the environmental effects confounded the underlying
genetics of the trait – e.g. a “quiet” bull, who was quiet
because he had been broken in, was still producing calves
with poor temperament). As genetic progress was made within
the breed for docility, the incidence of calves that needed
to be culled for poor temperament decreased.
Similarly, genetics can be used to improve the percentage of
females in the herd that are getting in calf, giving birth
to a live calf (unassisted), weaning the calf, and getting
back in calf. Let us explore which of the BREEDPLAN traits
are important for a maternal female throughout her life,
particularly during pregnancy, calving, while raising the
calf to weaning, and in maintaining her own condition.
1.
PREGNANCY
The first test, for any female, is to get in calf and carry
the calf to term. Ideally, a female should get pregnant in
the first or second cycle. This allows the producer to have
a short joining period (in a fertile herd, this shouldn’t
compromise pregnancy rates) and thus calve down over a
shorter time (reducing the number of weeks the producer
needs to check pregnant heifers and cows for calving
difficulties). Calves born from matings in the first or
second cycle also have a significant age, and thus weight,
advantage over their late-born herd mates.
Failure of a heifer to get pregnant is often due to her not
being sexually mature at the time she was out with the bull.
A heifer may not be sexually mature because she is a
late-maturing type (e.g. a tall, lanky animal), or because
she was born late in the season and is younger than the
other heifers (e.g. a small, young animal). In both
situations, the
fertility traits (Days
to Calving and Scrotal Size EBVs)
are important.
The
Days to Calving EBV
describes the genetic differences between animals in the
time from the start of the joining period (i.e., when the
female is introduced to the bull) until subsequent calving,
and is expressed in days. Most variation in this trait
occurs in how long it takes the female to get pregnant
(e.g., did she get pregnant in the first cycle, second
cycle, or not at all), with only a small amount of variation
in this trait being due to gestation length. Lower, more
negative Days to Calving
EBVs are more desirable, as they indicate shorter Days to
Calving (e.g., females that conceive earlier in the joining
period).
Similarly,
Scrotal Size EBVs
are another important indicator of fertility in the female
herd. While this may seem counterintuitive (after all, a
heifer does not have a scrotum), research has shown that
bulls with higher Scrotal Size EBVs tend to be more early
maturing than those with lower Scrotal Size EBVs. In turn,
bulls with higher Scrotal Size EBVs tend to have daughters
that mature earlier than the daughters of bulls with lower
Scrotal Size EBVs.
Thus, the ideal maternal female should have more negative
Days to Calving EBVs (indicating a shorter Days to Calving)
and more positive Scrotal Size EBVs.
2.
CALVING
The next important test for a female in
the breeding
herd is to give birth to a live calf, without assistance.
Calving difficulty has a negative impact on the
profitability of the herd due to increased mortality rates
(of calves, heifers, and sometimes, cows), slower
re-breeding performance, and considerable additional labour
and veterinary expenses.
While
non-genetic factors can contribute to calving difficulty
(it’s still important to keep heifers and cows in optimal
condition in the lead-up to calving), several genetic
factors also influence calving difficulty. These include
birth weight, gestation length, shape of the calf, pelvic
area, and willingness of the cow to push. These factors are
covered by several BREEDPLAN EBVs; namely,
Calving
Ease
Direct, Calving Ease Daughters,
Gestation Length, and Birth Weight.
The
Calving Ease
Direct EBV
describes the
genetic differences in the ability of a sire’s calves to be
born unassisted from two-year old heifers, while the
Calving
Ease
Daughters EBV
describes the
genetic differences in the ability of a sire’s two-year old
daughters to calve without assistance.
Both EBVs are
reported as differences in the percentage of unassisted
calvings, with higher,
more positive
Calving Ease EBVs
(indicating less calving difficulty) being more desirable.
In a self-replacing herd system, where daughters are
retained for breeding, both Calving Ease EBVs are of
importance. It is important to note that both traits relate
to calving difficulty as expressed in two-year old heifers,
a bull that has had no calving issues when mated to mature cows
may still cause trouble for heifers.
The
Gestation
Length EBV
describes the
genetic differences between animals in gestation length and
is expressed in days.
Lower, more
negative Gestation Length EBVs
indicate a
shorter gestation length and thus are
more desirable.
In
general, a shorter gestation length results in a smaller
calf, which is usually born with less difficulty than a
larger calf and also gives the cow a longer period to
rebreed without falling later and later in the breeding
season each year.
The
Birth Weight
EBV
describes the genetic differences between animals, regarding
calf birth weight, and is expressed in kilograms.
Small or
moderate Birth Weight EBVs are generally more favourable,
as
they indicate lighter birth weights. In general, a lighter
calf at birth is likely to result in less calving difficulty
than a heavier calf, although there can be exceptions. This
is because birth weight, as mentioned above, is not the only
factor that influences calving difficulty.
The ideal
maternal female should have more positive Calving Ease
Direct- and Calving Ease Daughters EBVs (indicating less
calving difficulty), more negative Gestation Length EBVs
(indicating shorter gestation length), and a low-to-moderate
Birth Weight EBV (indicating lower birth weight).
3.
RAISING THE CALF TO WEANING
The next test for the female is to raise her calf to
weaning. A good maternal cow should provide adequate
nutrition to raise the calf to weaning and wean her calf
with an adequate weaning weight. The
Milk EBV
provides an estimate of the maternal contribution of a dam
to the 200-day weight of her calf. The Milk EBV is expressed
in kilograms and indicates the expected difference in the
weight of the calf at 200 days due to the maternal
contribution of the cow.
However, it is important to note that the optimum Milk EBV
is dependent upon the production system and the environment
in which the cows are run. Selection for increased milk
production may be warranted when cows are run under good
nutritional conditions (e.g., improved pasture), while other
poorer environments (e.g., scrubby rangeland) may not
support cows with higher Milk EBVs. In addition,
high-milking cows may not get back in calf as easily as
lower-milking cows in the following year.
Thus, while the
ideal maternal female should provide adequate nutrition to
raise the calf to weaning, the optimum Milk EBV for a
maternal female will depend on the environment in which she
is raised.
4.
MAINTENANCE
In addition to
getting pregnant, giving birth to a live calf, weaning the
calf, and getting back in calf, a maternal cow should
perform all these tasks without consuming excessive amounts
of feed. Given that feed costs are one of the most expensive
costs on a farm, the weight of a mature cow will have a
major influence on net profitability. This is because, in
general, lighter cows will tend to eat less, thus having
lower feed requirements and being less expensive to
maintain. Conversely, given that live
weight is the major determinant in the value of cull cows,
heavier cows may provide higher returns when selling cull
cows. It is important to achieve an appropriate balance
between feed requirements over the lifetime of the cow and
her value as a cull animal.
The
Mature Cow
Weight EBV
describes the
genetic differences between cows in their live weight at 5
years of age and is expressed in kilograms. A higher, more
positive Mature Cow Weight EBV indicates an animal that
would produce progeny with a higher mature weight than an
animal with a lower Mature Cow Weight EBV. While producers
need to optimise the balance between feed requirement and
cull value, the ideal maternal female should have a low to
moderate Mature Cow Weight EBV, as this will reduce her feed
requirements over her lifetime.
Another trait
that gives a measure of cow maintenance is net feed intake.
Net
Feed Intake (NFI) EBVs
are measures of
genetic differences between animals in feed intake at a
standard weight and rate of weight gain. The
NFI-Post
Weaning (NFI-P) EBV
is a measure of
feed efficiency when animals are in a growing phase, while
the
NFI-Feedlot Finishing (NFI-F) EBV
is a measure of feed efficiency when animals are in a
feedlot finishing phase. For both NFI EBVs, a more negative
EBV indicates a more feed-efficient animal (e.g., the animal
consumes less feed than expected given its weight and growth
profile). While an EBV for net feed intake in cows is not
available, research has shown that there is a positive
relationship between NFI EBVs, feed intake, and feed
efficiency of cows. Simply put, selecting for more feed-
efficient animals using NFI EBVs should also lead to more
feed-efficient cows.
5.
OTHER TRAITS
In addition to the BREEDPLAN traits discussed above, it is
important to remember that other traits are important for a
good maternal cow in the herd. A good maternal cow must
still have
good structural soundness;
after all, she spends much of her life moving around the
paddock to feed and thus needs
good foot and leg structure
to allow her to move about with ease. In addition, a cow
with good structural soundness may
last longer
in the herd, thus potentially improving her longevity in the
breeding herd. Similarly, a maternal cow should be in
good general health.
While not strictly related to her maternal ability, the
horn/poll status, genetic condition status, and pedigree of
the cow
should also be considered. Keeping an eye on the pedigree of
the cow (and the bull she is being mated to) allows
producers to manage inbreeding in the herd at an acceptable
level. Similarly, producers may be interested in the genetic
condition status of the female, as this will allow them to
avoid carrier-to-carrier matings. Although this becomes less
important when the bulls being used in the herd have been
tested and found free of the relevant genetic conditions. In
the same way, producers breeding for polled animals may wish
to know the horn/poll status of the females to avoid
producing horned calves (unless using a homozygous polled
bull). This is less of a consideration for those wishing to
breed only horned calves, given that horns are recessive;
simply select bulls and females with visible horns.
SUMMARY
A
maternal female should get in calf, give birth unassisted to
a live calf, raise that calf to weaning, and then get back
in calf, all the while maintaining good condition, without
needing to consume excessive amounts of feed.
BREEDPLAN produces several EBVs that are of importance when
considering a maternal female; namely, Days to Calving,
Scrotal Size, Gestation Length, Calving Ease Direct, Calving
Ease Daughters, Birth Weight, Milk, and Mature Cow Weight.
Ideally, a maternal female will have shorter Days to Calving
and Gestation Length EBVs than average (more negative EBVs
are more desirable), while having larger Scrotal Size,
Calving Ease Direct, and Calving Ease Daughters EBVs (more
positive EBVs are more desirable). She should also have a
moderate Birth Weight (lower or moderate EBVs being more
desirable) and a moderate Mature Cow Weight (lower or
moderate EBVs being more desirable). The optimal Milk EBV
will depend on the environment, where producers in good
country may prefer more positive Milk EBVs, while producers
in more scrubby marginal country may prefer more moderate
Milk EBVs.
For further information on using genetics to breed maternal
females, or to further discuss any of the topics raised in
this article, please e-mail
extensions@abri.une.edu.au. |
