(Summarized from the BREEDPLAN MANUAL with some additions - CP Massmann)
Calving Ease is affected by many environmental factors and
several genetic ones. It is of course the genetic factors which BREEDPLAN can
assist to improve. They include:
CALF - weight and
COW - pelvic area and calving “will'.
Birth Weight EBV
Many studies have consistently shown birth weight to be by far
the most important, though calf shape and the maternal factors also need to be
considered for best genetic improvement. Individual birth weight can be used as
a guideline for calving problems, but birth weight EBVs are far better
predictors of calving problems since they combine data from different sources.
The accuracy of the bull’s birth weight EBV improves with an increase in the
number of progeny and his own birth weight becomes of minor importance.
Although LOW birth weight EBVs are favoured for calving
ease, they are also generally associated with lower overall growth potential.
Consequently, birth weight and growth need to be carefully balanced. Excessive
emphasis on low birth weight can lead to smaller (lower growth) heifers in the
next generation , i.e. the calves from the low birth weight bulls. These small
heifers may then tend to have more calving problems (i.e. lower maternal calving
ease) because their frame size and pelvic openings are not large enough. Hence
advantages from selecting for low birth weight will be lost by the maternal
component of calving ease.
Unless kept in check, birth weight will increase over time as a
result of selection for higher weights. There are, however, bulls with low or
average birth weight EBVs, yet high EBVs for the 200-day and 400-day weight
traits. PLEASE NOTE: these bulls are only identifiable if birth and subsequent
weights have been recorded.
REMEMBER: THE LOWER THE BIRTH WEIGHT EBV, THE LOWER
THE EXPECTED BIRTH WEIGHT.
that is used for the Breedplan Calving Ease EBVs
Calving ease codes:
The most important information
to generate accurate calving ease EBVs are scores for calving ease which are
recorded by all Breeders.
As outlined above, it has a
major influence on calving ease, and must therefore be part of any calving ease
prediction. Cows also influence birth weight
through the maternal environment
they provide in the uterus. This is called birth weight maternal. It is not
highly heritable, but has an effect and is also used in the analysis.
is another factor that is
genetically influenced. Calves carried for shorter terms, are generally born a
little lighter and therefore more easily. Gestation
length is however not yet
recorded by Simmentaler breeders.
The BREEDPLAN Calving Ease EBVs for Simmentalers are therefore
calculated from two sets of records which can be reliably taken and which exert
most influence on calving ease, viz:
Calving Ease Score
BREEDPLAN records, comparisons are initially only made from calving ease scores
in like treated groups. They are then combined with available Birth weight and
Gestation length information and the pedigree links and correlations are also
used in the calculation. The EBVs developed from this information allow
effect bulls have on the ease with which their calves are born. i.e. CALVING
EASE DIRECT (CED on certificate).
The calving ease
of a bull's daughters i.e. CALVING EASE DAUGHTERS (CEM on certificate).
Interpreting Calving Ease EBVsINTERPRETING
CALVING EASE EBVs
Calving Ease (CED)
– calving ease EBVs are estimates of genetic differences in the ability of
bulls’ calves from two-year-old heifers to be born unassisted. The EBVs are
reported as differences in the percentage unassisted calvings. Higher, more
positive, calving ease EBVs are more favourable – for example, a bull with
an EBV of +5.0% would be expected, on average, to produce 3% fewer difficult
calvings from 2 year old heifers than a bull with an EBV of –1.0% (6% difference
between the Sires, then halved as they contribute half the genetics).
Calving Ease (CEM)
– These EBVs are estimates of genetic differences among animals in the ability
of their two-year-old daughters to calve without assistance. The EBVs
are also reported as differences in the percentage of unassisted calvings.
Higher, more positive, calving ease EBVs are more favourable – for example,
a bull with an EBV of +4.0% would be expected to on average produce 2 year old
daughters that have 3% less calving problems than the daughters of a bull with
an EBV of –2.0%.
Bull Buying Exercise
exercise shows the format in which calving ease EBVs are presented and
demonstrates some principles of their use:
seeks a terminal sire to join with crossbred heifers, for yearling production.
Calving ease is of moderate importance.
Buyer 2 is
straight breeding for yearling production and wishes to improve calving ease of
is straight breeding and seeks a sire to join with heifers. Calving ease is of
considerable concern to this breeder of grass finished yearlings.
||Calving Ease (%)
Bull B (Positive CED with moderate accuracy and with the highest 400 day weight
Note: bull A has a
similar, but lower accuracy calving ease EBV; but lower 400 day weight.
Bull C (Positive
CEM EBV with acceptable 400 day weight)
Bull D (Positive
CEM with the highest accuracy, as calving ease is so critical. CEM average for
the retained females)
Note to bull breeders:
Will I get the same
result mating a +10 birth weight EBV sire with a O birth weight EBV cow (+10
and 0 / 2 = +5) as when I mate a +5 sire with a +5 cow (+5 AND +5 / 2 = +5)?
Over enough matings
the average birth weight EBVs will be the same (approximately +5). The +10/0
combination will, however, almost certainly cause more calving difficulty (and
dead calves) than the +5/+5 mating.