Page 6 - Ranui Angus 2021 ebook
P. 6


       An animal’s breeding value is its genetic merit, half of which will be passed on to its progeny.  While we will
       never know the exact breeding value, for performance traits it is possible to make good estimates.  These
       estimates are called Estimated Breeding Values (EBVs).
       In the calculation of EBVs, the performance of individual animals within a contemporary group is directly
       compared to the average of other animals in that group.  A contemporary group consists of animals of the
       same sex and age class within a herd, run under the same management conditions and treated equally.
       Indirect comparisons are made between animals reared in different contemporary groups, through the use
       of pedigree links between the groups.
       EBVs are expressed in the units of measurement for each particular trait.  They are shown as + ive or - ive
       differences between an individual animal’s genetics difference and the genetic base to which the animal is
       compared.  For example, a bull with an EBV of +50 kg for 600-Day Weight is estimated to have genetic merit
       50 kg above the breed base of 0 kg.  Since the breed base is set to an historical benchmark, the average
       EBVs of animals in each year drop has changed over time as a result of genetic progress within the breed.
       The absolute value of any EBV is not critical, but rather the differences in EBVs between animals.  Particular
       animals should be viewed as being “above or below breed average” for a particular trait.
       Whilst EBVs provide the best basis for the comparison of the genetic merit of animals reared in different
       environments and management conditions, they can only be used to compare animals analysed within the
       same analysis.  Consequently, TransTasman Angus Cattle Evaluation EBVs cannot be validly compared with
       EBVs for any other breed.
       Although EBVs provide an estimate of an animal’s genetic merit for a range of production traits, they do not
       provide information for all of the traits that must be considered during selection of functional animals.  In all
       situations, EBVs should be used in conjunction with visual assessment for other traits of importance (such
       as structural soundness, temperament, fertility etc).  A recommended practice is to firstly select breeding
       stock based on EBVs and to then select from this group to ensure that the final selections are otherwise
       EBVs are published for a range of traits covering fertility, calving ease, milking ability, growth, carcase
       merit and feed efficiency.  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
       the particular herd, markets and environment.  One of the advantages of having a comprehensive range of
       EBVs is that it is possible to avoid extremes in particular traits and select for animals with balanced overall
       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 % Direct = Direct Calving Ease - The EBV for direct calving ease indicates the influence of the sire on
       calving ease in purebred females calving at two years of age.
       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.

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