Page 9 - Pukenui 2020
P. 9

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