UNDERSTANDING

EBVs

FOR BETTER BALANCED BEEF

EBVs are published for a range of traits covering fertility, calving ease, maternal performance, growth and carcase merit. When using EBVs to assist in selection decisions it is important to achieve a balance between the different groups of traits and to place emphasis on those traits that are important to your herd, your markets, and your environment.

EBVs

Calving Ease EBVs (%) are based on calving difficulty scores, birth weights and gestation length information.  More positive EBVs are favourable and indicate easier calving.

CE % Daughters = Daughters’ Calving Ease – The EBV for daughters’ calving ease indicates how easily that sire’s daughters will calve at two years of age.

Gestation Length EBV (days) is an estimate of the time from conception to the birth of the calf and is based on AI and hand mating records.  Lower (negative) GL EBVs indicate shorter gestation length and therefore easier calving and increased growth after birth.

Birth Weight EBV (kg) is based on the measured birth weight of progeny, adjusted for dam age.  The lower the value, the lighter the calf at birth and the lower the likelihood of a difficult birth.  This is particularly important when selecting sires for use over heifers.

200-Day Growth EBV (kg) is calculated from the weight of progeny taken between 80 and 300 days of age.  Values are adjusted to 200 days and for age of dam.  This EBV is the best single estimate of an animal’s genetic merit for growth to early ages.

400-Day Weight EBV (kg) is calculated from the weight of progeny taken between 301 and 500 days of age, adjusted to 400 days and for age of dam.  This EBV is the best single estimate of an animal’s genetic merit for yearling weight.

600-Day Weight EBV (kg) is calculated from the weight of progeny taken between 501 and 900 days of age, adjusted to 600 days and for age of dam.  This EBV is the best single estimate of an animal’s genetic merit for growth beyond yearling age.

Mature Cow Weight EBV (kg) is based on the cow weight when the calf is weighed for weaning, adjusted to 5 years of age.  This EBV is an estimate of the genetic difference in cow weight at 5 years of age and is an indicator of growth at later ages and potential feed maintenance requirements of the females in the breeding herd.  Steer breeders wishing to grow animals out to a larger weight may also use the Mature Cow Weight EBV.

Milk EBV (kg) is an estimate of an animal’s milking ability.  For sires, this EBV indicates the effect of the daughter’s milking ability, inherited from the sire, on the 200-day weights of her calves.  For dams, it indicates her milking ability.

Scrotal Size EBV (cm) is calculated from the circumference of the scrotum taken between 300 and 700 days of age and adjusted to 400 days of age.  This EBV is an estimate of an animal’s genetic merit for scrotal size.  There is also a small negative correlation with age of puberty in female progeny and therefore selection for increased scrotal size will result in reduced age at calving of female progeny.

Days to Calving EBV (days) indicates the fertility of the daughters of the sire.  It is the time interval between the day when the female is first exposed to a bull in a paddock mating to the day when she subsequently calves.  A negative EBV for days to calving indicates a shorter interval from bull-in date to calving and therefore higher fertility.

Carcase Weight EBV (kg) is based on abattoir carcase records and is an indicator of the genetic differences in carcase weight at the standard age of 750 days.

Eye Muscle Area EBV (sq cm) is calculated from measurements from live animal ultrasound scans and from abattoir carcase data, adjusted to a standard 400 kg carcase.  This EBV estimates genetic differences in eye muscle area at the 12/13th rib site of a 400 kg dressed carcase.  More positive EBVs indicate better muscling on animals.  Sires with relatively higher EMA EBVs are expected to produce better-muscled and higher percentage yielding progeny at the same carcase weight than will sires with lower EMA EBVs.

Rib Fat and Rump Fat EBVs (mm) are calculated from measurements of subcutaneous fat depth at the 12/13-rib site and the P8 rump site (from live animal ultrasound scans and from abattoir carcases) and are adjusted to a standard 400 kg carcase.  These EBVs are indicators of the genetic differences in fat distribution on a standard 400 kg carcase.  Sires with low, or negative, fat EBVs are expected to produce leaner progeny at any particular carcase weight than will sires with higher EBVs.

Retail Beef Yield EBV (%) indicates genetic differences between animals for retail yield percentage in a standard 400 kg carcase.  Sires with larger EBVs are expected to produce progeny with higher yielding carcases.

Intramuscular Fat EBV (%) is an estimate of the genetic difference in the percentage of intramuscular fat at the 12/13th rib site in a 400 kg carcase.  Depending on market targets, larger more positive values are generally more favourable.

Docility EBV (%) is an estimate of the genetic differences between animals in temperament.  Docility EBVs are expressed as differences in the percentage of progeny that will be scored with acceptable temperament (ie. either “docile” or “restless”).

There are currently three selection indexes calculated for Angus New Zealand animals. These are Self-Replacing, AngusPure and Heifer/Dairy Terminal. Each selection index describes a different production/market scenario and relates to a typical commercial herd in New Zealand that is targeting the following specifications.

Selection Indexes

Index values are reported as EBVs, in units of relative earning capacity ($) for a given market. They reflect both the short-term profit generated by a sire through the sale of his progeny, and the longer-term profit generated by his daughters in a self-replacing cow herd. More information is available on selecting animals using a selection index. The Index values are derived using BreedObject technology. More information is available from the BreedObject web site.

Self-Replacing Index ($) – Estimates the genetic differences between animals in net profitability per cow joined in an example self-replacing commercial herd that targets the production of grass finished steers.  Steers are assumed marketed at approximately 480 kg live weight (265 kg carcase weight and 7 mm fat depth) at approximately 16 months of age. Selected heifers are retained for breeding and the balance marketed at approximately 16 months weighing 415 kgs (230 kg carcase weight and 8 mm fat depth) As some daughters are retained, maternal traits are also of importance.

AngusPure Index ($) – Estimates the genetic differences between animals in net profitability per cow joined in an example self-replacing commercial Angus herd that targets the production of grass finished steers for the AngusPure programme.  Steers are assumed marketed at 530 kg live weight (290 kg carcase weight and 10 mm fat depth) at approximately 20 months of age. Selected heifers are retained for breeding and the balance marketed at approximately 20 months weighing 450 kg (240 kg carcase weight and 10 mm fat depth). A significant premium for carcase quality was assumed and, as some daughters are retained, maternal traits are also of importance.

Heifer/Dairy Terminal Index ($) – Estimates the genetic differences between animals in net profitability per female joined in an example herd where all progeny are marketed. All progeny are marketed at approximately 510 kg live weight (280 kg carcase weight and 7 mm fat depth) at approximately 24 months of age.

Note that $Index values for individual animals are sensitive to the assumptions used in the BreedObject analysis to calculate the selection index.  More information is available on the weightings used in the Angus New Zealand Selection Indices.

Accuracy

Accuracy (%) is based on the amount of performance information available on the animal and its close relatives – particularly the number of progeny analysed.  Accuracy is also based on the heritability of the trait and the genetic correlations with other recorded traits.  Hence accuracy indicates the “confidence level” of the EBV.  The higher the accuracy value the lower the likelihood of change in the animal’s EBV as more information is analysed for that animal or its relatives.  Even though an EBV with a low accuracy may change in the future, it is still the best estimate of an animal’s genetic merit for that trait.  As more information becomes available, an EBV is just as likely to increase in value, as it is to decrease.

Accuracy values range from 0-99%. The following guide is given for interpreting accuracy:

Accuracy RangeInterpretation
less than 50%EBV should be considered as a preliminary estimate.
It could change substantially as more performance information becomes available.
50-74%Medium accuracy, usually based on the animal’s own records and pedigree.
Still subject to substantial changes with more information,
particularly when the performance of progeny are analysed.
75-90% Medium – high accuracy and includes some progeny information. 
Becoming a more reliable indicator of the animal’s value as a parent.
more than 90% High accuracy estimate of the animal’s true breeding value. 
It is unlikely that the EBV will change much with the addition of more progeny data.

As a rule, animals should be compared on EBVs regardless of accuracy. However, where two animals have similar EBVs the one with higher accuracy could be the safer choice, assuming other factors are equal.

For further information please contact AngusNZ or TACE.