Minimising Calving Difficulties
Calving difficulties (dystocia) contributes heavily to production losses in suckler
herds. The obvious losses are due to calves or cows that die at or soon after calving.
Studies from the USA have shown have that calves which experience difficult births
are 4 times more likely to be born dead or die within the 1st 24 hours of birth
compared to those born without difficulty.
Table 1 – Comparison of calf mortality rates
Calving Difficulty Unassisted Normal Calving
Study 1 16% death rate
4% death rate
Study 2 20% death rate
5% death rate
Study 3 11.7% death rate
3% death rate
Less noticeable losses that are due to calving difficulties include delayed return to
heat, poorer conception rates and subsequent higher barren rates and extended
calving patterns. Labour and vet and med cost also escalate the more problems you
have. While occasional calving problems are almost unavoidable, minimising dystocia
by careful management and selection of genetics will obviously improve calf survival
rates and the profitability of your herd.
Many factors influence the incidence of dystocia, but broadly they can be spit into
two groups.
1. Factors affecting the size and shape of the calf
2. Factors affecting the ability of the cow to give birth
The interaction between these two groups determines the likelihood of problems.
Factors Affecting Calf Size and Shape
CALF BIRTH WEIGHT
The bigger the calf the bigger the problem and it is no surprise to anyone that as
birth weights increase the number of assisted calvings increase. It therefore follows
that a reduction in dystocia can by achieved by producing calves of a lower birth
weight. But as birth weight is highly correlated to growth rates a lot of producers
may strive to “challenge” their cows by choosing matings that result in birth weights
near to the threshold of their herd.
As long as this threshold is not exceeded, this practice will keep dystocia at a
manageable level and maximise calf performance. As a guide, producers should be
aiming for calf birth weights of 6-8% of the weight of their mothers.
(600kg cow - 36 – 48kg calf).
BREED AND GENETICS OF SIRE
Few farmers would dispute that calf shape affects ease or difficulty of birth. In
Simmental bulls work has shown that their chest girth size at year of age is highly
correlated to subsequent ease of calving of their offspring. Another example is the
Belgian Blue and other double muscled breeds, or bloodlines within breeds that have
this trait. Bulls that produce calves that are “smooth” in appearance (correct
shoulder placement, absence of coarse muscling) produce calves that are born more
easily than the opposite type even if their birth weights are identical.
POSITION AND PRESENTATION IN THE UTERUS
Most calves are presented front feet first with the nose resting on the front legs.
Occasional the calf will be abnormal presented (head back, breach etc), and will need
assistance. Abnormal presentations are thought to be repeatable (cows that have
had one abnormal presentation are more likely to do it again), but there is little that
can be done to reduce the small percentage of calves that experience dystocia due
to abnormal presentations.
Factors Affecting the Ability of the Cow to Give Birth
COW’S PELVIC AREA
It makes sense that cows with small pelvises that carry large calves will experience
calving difficulties and opposite for cows with large pelvises and small calves. Pelvic
area is roughly correlated to frame size, but it should not be assumed that a big cow
has a big pelvis, think of the Jersey cow. The only way is to make a direct
measurement of the cow’s pelvis. Some producers are now making use pelvic
measurements to cull replacement heifers with small pelvis. As pelvic size is a
heritable trait, like growth rates. Removal of animals with inadequate pelvic area will
help over time produce a reduction in dystocia
AGE AND BREED OF COW
Heifers account for the majority of calving difficulties and associated calf losses,
despite often being more closely observed, and assisted more readily at calving than
mature cows.
Replacement heifers must be fed to grow and develop rapidly enough so that they
cycle and become pregnant early enough to calve at 24 months of age. The further
advantage of this is they will closer to their mature skeletal size when they calve for
the 1st time. As a rule of thumb heifers should be 65% of expected adult weight at
bulling and 85% of adult weight at calving. Weighing heifers occasionally and adjusting
diets will help produce the desired gains without making heifers too fat.
Breed of cow obviously influences ease of calving; but within breeds differences are
due to pelvic area, muscling and fatness.
NUTRITION & CONDITION
Some farmers try to limit feed prior to calving in order to reduce birth weights and
dystocia. This will reduce birth weights, but as it will limit cow nutrition it can
actually increase calving problems as underfed cows will struggle to progress through
a normal calving despite having a lighter calf. Additional as underfed cows will take
longer to return to heat this practice is not recommended.
Aim instead to maintain condition avoiding excessive body condition loss or gain.
Spring calving cows aim for a condition score 2-2.5, autumn calvers aim for a
condition score of 3.
Genetics – Estimated Breeding Values
Genetic solutions are not straight forward as the heritable of calving ease is fairly
low as it is influenced by management, feeding and season of calving, hence it can be
hard to predict in an individual animal. It can be improved by comparing information
from different sources. These sources include the animals own records for calving
ease, its contemporaries in the same herd, those of relatives in other herds and also
the animals and relatives genetic merit for other recorded traits (e.g. birth weights,
200 day weight, 400 day weight, gestation length, muscle score and muscle depth.)
This will improve the accuracy of the animals calving ease EBV and birth weight EBV
which then can be used as tools in reducing the incidence of dystocia along with
other physical performance traits to maximise the productivity of your herd.
Recommendations for Reducing Dystocia
1. Mate bulling heifers and small cows to bulls that will sire small calves.
2. Consider the breed, estimated birth weight variation, actual birth weight,
calving ease and physical structure of the bull.
3. Aim to calve heifers down at 85% of their expected mature weight.
4. Monitor body condition score and target spring calving cows to be in BCS 22.5 at calving, autumn calving cows to be in BCS 3.
5. Consider measuring pelvic area in replacement heifers and culling those that
are too small if your herd has had problems. Target pelvic area sizes will vary
from one breed to the next. As a rule of thumb heifers of medium sized
breeds should have pelvises of at least 160 cm2 at breeding, larger breeds 180
cm2 or more.
6. Don’t retain daughters of cows that have a record of calving difficulties.
7. Aim to calve heifers 21-30 days prior to the planned start of calving for cows.
It will allow more observation of heifers and allow them an extra period to
resume cycling prior to bulling.
8. Feeding the herd later in the day will encourage more cows to calve in
daylight.
9. Keep a record of calving ease for calves you observe born. If this changes
over time consider reasons for this.
10. When assisting cows at calving. Provide adequate time for a cow or heifer to
calve prior to interfering. Don’t rush in.
11. House assisted calves for a few days post calving. Studies have shown that
this improves their chance of survival than if left outdoors in the immediate
period post calving. If housing is limited these should be top priorities.