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 progeny.
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 characteristics.
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 to readers.
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 high birth weight bull. So far so good, most people realize this.
2. More confusingly, Birth Weight has a moderate positive correlation 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 correlation with 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 (DIRECT) genetics.
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 for this:
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.
(This article is the property of Millah Murrah Angus and may not be reproduced without express permission of the writer. Views expressed herein are the writer’s opinion only and no liability is assumed for action taken by others based on this article.)