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Calving Ability

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					HEALTH TRAIT SERIES



      Calving Ability
      A NEW PLAN TO ADDRESS AN OLD PROBLEM                                                                                               Kent Weigel
                                                                                                                                     University of Wisconsin
    A system for gathering farmer-assigned           breeding stock, and large calves tend to         calf heifers are considered as ‘difficult’,
    scores for calving difficulty, also known as      win blue ribbons. We could learn a lot from      corresponding to scores of 4 or 5 on a five-
    “dystocia”, was devised in the late 1970s,       our counterparts in the beef industry with       point scale, as compared with about 3% of
    and sire rankings for calving ease have been     regard this trait, as they learned early on      births involving second and later lactation
    available for more than two decades. The         how to identify bulls that could sire calves     cows. Likewise, about 13% of calves from
    sire evaluations that have been provided         with low birth weights that can, in turn,        first-calf heifers will be born dead or will
                           g
    refer to ‘direct calving ease’ (i.e., measured   grow very rapidly to achieve acceptable          die by 48 hours of age, as compared with
    as a trait of the calf), which is essentially    weaning or yearling weights.                     about 6.5% of calves from second and later
    a proxy for calf size. This information                                                           lactation cows. As shown in the example
    has been extremely valuable for dairy            Some major steps have been taken to              bulls listed below, tremendous genetic
    producers, because it has allowed them to        address the issue of calving problems in         variation exists for these four traits.
    identify ‘calving ease bulls’ that can safely    the past three years, with the introduction
    be used as mates for yearling heifers.           of national sire evaluations for three new       Calving ease evaluations are published in
                                                                                           g
                                                     traits. The first is ‘maternal calving ease’      terms of the expected percentage of difficult
    Despite the widespread use of calving ease       (i.e., measured as a trait of the cow),          births in heifers. For example, when
    information, little or no progress has been      which reflects the cow’s ability to have          014HO04099 Billion is mated to yearling
    made in reducing the overall incidence of        a calf without assistance from the farmer        heifers, 5% of the calves will be born with
    calving problems in the Holstein breed.          or veterinarian. The second is ‘direct           difficulty, whereas 12% of the calves will
    The reason is two-fold. The first reason is       stillbirth rate’, which measures the calf’s      be born with difficulty when 014HO03854
    educational – the advice given to farmers        ability to survive the birthing process and      Disco is used as a mate for yearling heifers.
    has been to use calving ease data to identify    the neonatal period (up to 48 hours of           Likewise, when 014HO02586 Sailor
    bulls that are safe as mates for yearling        age). The third is ‘maternal stillbirth rate’,   daughters grow up and calve for the first
    heifers. The implicit recommendation has         which reflects the cow’s ability to produce       time, about 5% of their calves will be born
    been that the remaining bulls (i.e., those       a live, healthy calf.                            with difficulty, whereas heifers sired by
    that are not safe because they sire large                                                         014HO04280 Professor will have difficulty
    calves that cause dystocia) should be used       In practice, these four measures of calving      at first calving about 10% of the time.
    as mates for lactating cows. As a result, the    ability are referred to as service sire
    genes that cause large calf size and dystocia    calving ease (SCE), daughter calving ease        Stillbirth evaluations are published in terms
    remain at high frequency in the population.      (DCE), service sire stillbirth rate (SSB),       of the expected percentage of dead calves
    The second reason is intentional – many          and daughter stillbirth rate (DSB). On
    Holstein breeders show cattle or sell            average, about 8% of births involving first-         Article continued on page 5.

    Table 1. Service Sire & Daughter Calving Ease and Stillbirth Examples
                                                                  Direct              Maternal                 Direct                     Maternal
                                                              (Service Sire)         (Daughter)           (Service Sire)                (Daughter)
                                                               Calving Ease         Calving Ease          Stillbirth Rate              Stillbirth Rate
                                                                  (SCE)                (DCE)                   (SSB)                        (DSB)
      014HO04099 BILLION                                            5%                   6%                     8.4%                         9.7%
      014HO03854 DISCO                                             12%                  11%                     7.3%                         5.9%
      014HO02586 SAILOR                                             6%                   5%                     9.6%                         8.1%
      014HO04280 PROFESSOR                                         11%                  10%                     8.7%                        10.8%
      014HO03571 DUTCH SCORE                                        7%                   6%                     6.4%                         6.0%
      014HO03738 MATT                                               6%                   6%                    10.0%                         6.2%
      014HO03597 POTTER                                             6%                   5%                     7.7%                         4.8%
      014HO04131 WRANGLER                                           7%                   9%                     8.9%                        13.4%
                                                                                                                         Source: January 2008 USDA/Holstein Association/NAAB

2                                                                                                                                          Genetic Trends - April 2008

				
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