Page 9 - Oct12020

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
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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-
year-old.
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