Page 9 - Oct12020
P. 9

Selecting Replacement                                                                       The Midwest Cattleman · October 1, 2020 · P9

      Heifers Based on Birth

      Date and Age of Dam

      By Aaron Berger, Nebraska Extension Beef Educator
         Two research studies at the  rate as a two-year-old during  more            calves
      University of Nebraska by Dr.  her  second  breeding  season.  had pregnan-
      Rick Funston, beef reproduc- Heifers born to first-calf heif- cy rates of 84%
      tive physiologist at the West  ers only had a 58% pregnancy  in their second
      Central Research and Exten- rate in their second breed-
      sion Center, suggest that the  ing season. Heifers born to                 continued on
                                                                                      page 16
      key  information  needed  to  cows that already had one or
      identify heifers most likely to
      be successful as replacements
      is knowing the day the heifers
      are born.
         The 2012 Nebraska Beef
      Cattle Report “Effect of Calv-
      ing Period on Heifer Progeny”
      and the 2016 Nebraska Beef
      Cattle Report “Effect of Dam
      Age  on Offspring  Productivi-
      ty” demonstrate that the date
      in a calving season when a
      heifer is born, as well as the
      age of her dam, significantly
      influence her success in be-
      coming pregnant as a year-
      ling heifer and subsequently
      becoming pregnant as a two-
      Birth date
         The “Effect of Calving Pe-
      riod on Heifer Progeny” study
      found that
         •heifers born in the first 21
      days of the calving season had
      an average pregnancy rate of
      90% as yearlings,
         •heifers born in the second
      21-day period had an 86%
      pregnancy rate, and
         •heifers born in the third
      21-day period had a 78%
      pregnancy rate.
         The pregnancy rate for
      these heifers in their second
      breeding season was 93%,
      90% and 84% respectively
      based on the heifer’s birth
      date being in the first, second
      or third 21-day interval of the
      calving season. In this study,
      heifer calves born in the first
      two 21-day calving intervals
      are older and more likely to
      conceive in the first breed-
      ing season. They also have an
      advantage in conceiving as a
      two-year-old in their second
      breeding season.
      Age of dam
         In the “Effect of Dam Age on
      Offspring Productivity” study,
      the age of a heifer’s dam when
      she is born significantly influ-
      enced a heifer’s pregnancy
   4   5   6   7   8   9   10   11   12   13   14