Calving Ease (direct)
The ability of a two year old heifer to calve to this animal.
Calving Ease (daughters)
The ability of the subject animal’s two year old daughters
to calve without assistance
Average number of days from conception to birth of an animal’s
Average weight of an animal’s progeny at birth
Whole Herd Calving Ease
For cow/calf operations, in economic terms, herd wide calving ease
is a vastly more important issue than say, consideration of carcass
Presently the application of EBV’s to whole herd or inherent
calving ease is not well understood or promoted in the Australian industry. We
have gone to some lengths here to give explanations and food for thought
Breeders need to grasp the underlying trait
correlations involved in
calving ease. Reference to the correlation graphs (taken from the Angus
Society Web site) shown at the end of
this document indicate the following:
1. Birth Weight has a strong negative correlation with Calving
Ease (DIRECT). This means if all other variables are equal then a low
birth weight bull will give heifers an easier time at calving than a
weight bull. So far so good, most people realize this.
2. More confusingly, Birth Weight has a moderate
with Calving Ease (DAUGHTERS). This means if all other variables are
equal then the heifer progeny of a low birth weight bull will
have a harder time at calving than progeny of a high birth weight bull.
3. Most importantly, and a fact often neglected in breeding discussion,
is that Calving Ease (Direct) has a strong negative
Calving Ease (Daughters). This means if all other variables are equal
then using high Calving Ease (DIRECT) genetics will produce more
calving ease problems in descendant generations than low Calving Ease
To summarize, routinely using low birth weight and calving ease (direct)
sires is effectively selecting against whole herd or inherent calving
ease. (That is not to say there aren’t situations where it is sensible
to employ a low birth/high calving ease sire.)
Putting the theory into practical terms there seems to be two reasons
1. As they inherit 50% of the birth/calving ease genetics from the sire
(which in general terms implies small and narrow bulls), the female progeny
of so called “heifer bulls” are often narrower throughout
and do not grow out adequately by joining age. The result is inhibition
of pelvic development up to time of birth.
2. By using low birth/high calving ease sires and achieving 0% dystocia,
there is insufficient pressure placed on two year old heifers at calving.
Nil calving difficulties means there is no annual screening process to
weed out the poor calving genetics within the herd.
To maintain the inherent calving ease of a cow herd, it is best to complement
the course of nature with the use of the technology available in the
form of EBV’s. In the wild, heifers are mated on a first come,
first served basis (the other way around in fact!). Breedplan is useful,
as it allows us to preclude extreme events, such as the equivalent of
a +12 birth weight bull mating with a virgin heifer. We can use Breedplan
to form reasonable parameters for challenging our heifers whilst replicating
nature within our herd. Within this framework it is often sensible to
employ minimum limits for birth weight as well as maximums. This will
ensure the heifers are sufficiently challenged to bring about an acceptable
proportion of calving difficulties, thus creating the screening process
mentioned in point 2 above. Implementing this philosophy will ensure
long term, optimum, herd wide calving ease.
As a guide, at Millah Murrah when considering sires for our heifers,
we join them to the same sires as the cows. In EBV terms we are open-minded
but usually this means a birth weight EBV somewhere between +2 and +7.
Our belief is that birth weight and calving ease EBV’s are of
secondary importance to prudent heifer management in determining the
calving ease outcome each season.
There is though, no doubt that traditional “heifer bulls” are
counterproductive to establishing long term built in calving ease for
a breeding operation. Furthermore, when considering birth weight in bulls
for use over cows only, there are situations where, up to the point where
dystocia (other than breach calving) becomes apparent in cows, there
is only upside gain to be had from selecting high birth genetics.
As with all breeding decisions, choosing a sensible balance is the best
approach and individuals will have varying opinions as to what is best.
Calves grow fastest later in the pregnancy.
It is possible to see a three week spread in the gestation length of
calves conceived on the same date.
The effect of short gestation length then, is easier calving and more
time for recovery for the mother. So short gestation length has
a positive effect on calving ease and herd fertility.
Gestation length EBV’s are seldom given the recognition they deserve.
Short gestation genetics are essentially free, that is they have no detrimental
side effects (except where their influence makes birth weights lower
than desirable). Breeders are wise to pay attention to this trait when
examining EBV’s, especially for heifer mating decisions.
Calving Ease (Daughters)
The only reason this trait is not given greater “air time” is
that it takes so long to derive EBV’s of useful accuracy for an
animal. Sale age bulls will often have no EBV given for this trait and
where a number is available it will be of very low accuracy. Nevertheless
any EBV is better than none and breeders should be conscious to improve
this trait within their herd. For Breedplan recorded herds it is an EBV
of great importance as it indicates the herd wide calving ease position
via a genetic trend graph. Individual estimates for each active female
are also provided.
Summary of Calving Ease Management
Focusing on low birth weight “heifer bulls” is counterproductive
to establishing inherent, herd wide calving ease.
Focusing on high calving ease (direct) “heifer bulls” is
counterproductive to establishing inherent, herd wide calving ease.
Optimum level of dystocia is >0. Need to create a screening process
to sift out poor calving genetics and allow nature to take its course.
- Short Gestation length enhances calving ease (direct) and herd fertility
Calving Ease (daughters) is an important trait, especially where it can
be measured across the herd, as in genetic trend graphs for Breedplan
recorded herds. Any CE(dtrs) EBV’s for sale bulls will be low
accuracy, but best estimate available.
- Nothing can substitute for good heifer management to minimize dystocia.