Performance Testing

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(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 shape                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.

Information that is used for the Breedplan Calving Ease EBVs

1.  Calving ease codes:  The most important information to generate accurate calving ease EBVs are scores for calving ease which are recorded by all Breeders.   
2. 
Birth Weight:   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.

3.  Gestation length 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                     Birth Weight

Like all 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 predictions for:

    ■  The direct 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

The following exercise shows the format in which calving ease EBVs are presented and demonstrates some principles of their use:

Buyer 1 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 the females. 
Buyer 3 is straight breeding and seeks a sire to join with heifers.  Calving ease is of considerable concern to this breeder of grass finished yearlings.

Sire Birth Wt 400d Wt Calving Ease (%)
Kg Acc Kg Acc Direct (CED) Daughters (CEM)
                 
A +.2 65% +6 60% +10 35% -6 30%
B +.5 79% +25 75% +9 67% -9 51%
C +1.3 83% +21 80% +1 58% +5 60%
D +0.7 95% +18 93% +8 85% 0 75%
 Breed av +1   +16   0   0

Answers

Buyer 1
Bull B (Positive CED with moderate accuracy and with the highest 400 day weight EBV).

Note: bull A has a similar, but lower accuracy calving ease EBV; but lower 400 day weight.
 

Buyer 2

Bull C (Positive CEM EBV with acceptable 400 day weight)

 

Buyer 3

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.

 

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