Page 36 - Hillcroft Catalogue 2021 ebook

ESTIMATED BREEDING VALUES (EBVS) EXPLAINED

EBVS Mature Cow Weight EBV (kg) is based on the cow weight when the
An animal’s breeding value is its genetic merit, half of which will be passed calf is weighed for weaning, adjusted to 5 years of age. This EBV is an
on to its progeny. While we will never know the exact breeding value, estimate of the genetic difference in cow weight at 5 years of age and
for performance traits it is possible to make good estimates. These is an indicator of growth at later ages and potential feed maintenance
estimates are called Estimated Breeding Values (EBVs). requirements of the females in the breeding herd. Steer breeders wishing
In the calculation of EBVs, the performance of individual animals within a to grow animals out to a larger weight may also use the Mature Cow
Weight EBV.
contemporary group is directly compared to the average of other animals
in that group. A contemporary group consists of animals of the same sex Milk EBV (kg) is an estimate of an animal’s milking ability. For sires, this
and age class within a herd, run under the same management conditions EBV indicates the effect of the daughter’s milking ability, inherited from
and treated equally. Indirect comparisons are made between animals the sire, on the 200-day weights of her calves. For dams, it indicates her
reared in different contemporary groups, through the use of pedigree links milking ability.
between the groups. Scrotal Size EBV (cm) is calculated from the circumference of the
EBVs are expressed in the units of measurement for each particular scrotum taken between 300 and 700 days of age and adjusted to 400
trait. They are shown as + ive or - ive differences between an individual days of age. This EBV is an estimate of an animal’s genetic merit for
animal’s genetics difference and the genetic base to which the animal is scrotal size. There is also a small negative correlation with age of puberty
compared. For example, a bull with an EBV of +50 kg for 600-Day Weight in female progeny and therefore selection for increased scrotal size will
is estimated to have genetic merit 50 kg above the breed base of 0 kg. result in reduced age at calving of female progeny.
Since the breed base is set to an historical benchmark, the average EBVs Days to Calving EBV (days) indicates the fertility of the daughters of
of animals in each year drop has changed over time as a result of genetic the sire. It is the time interval between the day when the female is first
progress within the breed. exposed to a bull in a paddock mating to the day when she subsequently
The absolute value of any EBV is not critical, but rather the differences calves. A negative EBV for days to calving indicates a shorter interval
in EBVs between animals. Particular animals should be viewed as being from bull-in date to calving and therefore higher fertility.
“above or below breed average” for a particular trait. Carcase Weight EBV (kg) is based on abattoir carcase records and is
Whilst EBVs provide the best basis for the comparison of the genetic an indicator of the genetic differences in carcase weight at the standard
merit of animals reared in different environments and management age of 750 days.
conditions, they can only be used to compare animals analysed within the Eye Muscle Area EBV (sq cm) is calculated from measurements from
same analysis. Consequently, NZ ANGUS TACE EBVs cannot be validly live animal ultrasound scans and from abattoir carcase data, adjusted to
compared with EBVs for any other breed. a standard 400 kg carcase. This EBV estimates genetic differences
Although EBVs provide an estimate of an animal’s genetic merit for a in eye muscle area at the 12/13th rib site of a 400 kg dressed carcase.
range of production traits, they do not provide information for all of the More positive EBVs indicate better muscling on animals. Sires with
traits that must be considered during selection of functional animals. In all relatively higher EMA EBVs are expected to produce better-muscled and
situations, EBVs should be used in conjunction with visual assessment for higher percentage yielding progeny at the same carcase weight than will
other traits of importance (such as structural soundness, temperament, sires with lower EMA EBVs.
fertility etc). A recommended practice is to firstly select breeding stock Rib Fat and Rump Fat EBVs (mm) are calculated from measurements
based on EBVs and to then select from this group to ensure that the final of subcutaneous fat depth at the 12/13-rib site and the P8 rump site (from
selections are otherwise acceptable. live animal ultrasound scans and from abattoir carcases) and are adjusted
EBVs are published for a range of traits covering fertility, calving ease, to a standard 400 kg carcase. These EBVs are indicators of the genetic
milking ability, growth, carcase merit and feed efficiency. When using differences in fat distribution on a standard 400 kg carcase. Sires with
EBVs to assist in selection decisions it is important to achieve a balance low, or negative, fat EBVs are expected to produce leaner progeny at any
between the different groups of traits and to place emphasis on those particular carcase weight than will sires with higher EBVs.
traits that are important to the particular herd, markets and environment. Retail Beef Yield EBV (%) indicates genetic differences between
One of the advantages of having a comprehensive range of EBVs is that it animals for retail yield percentage in a standard 400 kg carcase. Sires
is possible to avoid extremes in particular traits and select for animals with with larger EBVs are expected to produce progeny with higher yielding
balanced overall performance. carcases.
Calving Ease EBVs (%) are based on calving difficulty scores, birth weights Intramuscular Fat EBV (%) is an estimate of the genetic difference
and gestation length information. More positive EBVs are favourable and in the percentage of intramuscular fat at the 12/13th rib site in a 400 kg
indicate easier calving. carcase. Depending on market targets, larger more positive values are
CE % Direct = Direct Calving Ease - The EBV for direct calving ease generally more favourable.
indicates the influence of the sire on calving ease in purebred females Docility EBV (%) is an estimate of the genetic differences between
calving at two years of age. animals in temperament. Docility EBVs are expressed as differences in the
CE % Daughters = Daughters’ Calving Ease - The EBV for percentage of progeny that will be scored with acceptable temperament
daughters’ calving ease indicates how easily that sire’s daughters will (ie. either “docile” or “restless”).
calve at two years of age. ACCURACY
Gestation Length EBV (days) is an estimate of the time from Accuracy (%) is based on the amount of performance information
conception to the birth of the calf and is based on AI and hand mating available on the animal and its close relatives - particularly the number
records. Lower (negative) GL EBVs indicate shorter gestation length and of progeny analysed. Accuracy is also based on the heritability of the
therefore easier calving and increased growth after birth. trait and the genetic correlations with other recorded traits. Hence
Birth Weight EBV (kg) is based on the measured birth weight of accuracy indicates the “confidence level” of the EBV. The higher the
progeny, adjusted for dam age. The lower the value, the lighter the calf accuracy value the lower the likelihood of change in the animal’s EBV as
at birth and the lower the likelihood of a difficult birth. This is particularly more information is analysed for that animal or its relatives. Even though
important when selecting sires for use over heifers. an EBV with a low accuracy may change in the future, it is still the best
200-Day Growth EBV (kg) is calculated from the weight of progeny estimate of an animal’s genetic merit for that trait. As more information
taken between 80 and 300 days of age. Values are adjusted to 200 days becomes available, an EBV is just as likely to increase in value, as it is to
and for age of dam. This EBV is the best single estimate of an animal’s decrease.
genetic merit for growth to early ages. Accuracy values range from 0-99%. The following guide is given for
400-Day Weight EBV (kg) is calculated from the weight of progeny interpreting accuracy:
taken between 301 and 500 days of age, adjusted to 400 days and for As a rule, animals should be compared on EBVs regardless of accuracy.
age of dam. This EBV is the best single estimate of an animal’s genetic However, where two animals have similar EBVs the one with higher
merit for yearling weight. accuracy could be the safer choice, assuming other factors are equal.
600-Day Weight EBV (kg) is calculated from the weight of progeny For further information please contact NZ Angus or TACE.
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.