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Development of replacement heifers--Beth Blevins, DVM

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Faster horses

Well-known member
Feb 11, 2005
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NE WY at the foot of the Big Horn mountains
There has been quite a few discussions on this forum regarding
development of replacement heifers. The following was an article
in the Mt. Angus News, written by Beth M. Blevins, DVM. I thought
the folks here would find it interesting:

One chore for fall
involves selection of replacement heifers and development of those heifers. The tendency to choose the large well doing heifers results from eye appeal. The biggest heifers just attract the most attention. Consistently choosing the largest heifers tends to increase frame score
on the herd. A hip height of 47 to 50" for a 10 month old heifer
would be a frame score of 5 or 6 which is a moderate frame score.
At 20 months that same heifer should have a hip height of 50 to 52"
as measured when the heifer is standing square, sighted at the hook
bones. Having an idea of the
desired frame score on the cow herd or even knowing the average height in the cow herd now and whether an
increase, decrease or maintenance of that frame is desired helps
determine a target weight for replacement heifers. Having a target
weight for the heifers gives a producer a tangible goal. Angus heifers,
as well as other breeds that are not Brahma or Brahma-cross, reach
puberty at 60-65% of their mature weight. Using the frame score to predict mature weight then allows computation of a target weight for puberty. For example a frame score of 5 in a 10-month old heifer
should have a hip height of about 48" and a mature weight of
1173#. Sixty percent of 1173# is 704# as the target weight for
puberty. Hitting the target weight at the start of the breeding season
gives that heifer the best chance of breeding. Ideally heifers
should have an average daily gain from weaning to the start of
1 to 1.5# per day. Adequate, but not excessive, gains ensure proper udder development and milking ability. Protein and energy requirements
met in a balanced ration to achieve a body conditon score of
6 is ideal. Heifers gaining on average from weaning to breeding, more
than 2# per day had decreased fertility as did thin heifers. In addition,
the fatter
heifers have a decrease in lifetime weaning weights because of decreased milk production. If heifers are thin for part of the period from weaning
to breeding, then fed more to hit the target weight, the fertility and
milking ability are preserved. Looking at the entire weaning to
breeding period for the average of 1 to 1.5# daily gain and reaching
the target weight with a body condition of 6 is vital.

Measuring pelvic area as a selection criteria for heifers facilitates the process if properly interpreted. Simply choosing the heifers with the
largest pelvic area will result in selecting for larger frame score. Unfortunately the larger frame score heifer has a larger frame
score calf and calving problems still encountered. Pelvic measurements taken with a caliper inserted rectally, finds the narrowest height
and width in centimeters. The product of those measurements yields
the pelvic area in centimeters. Instead of choosing bigger is better,
the best use of pelvic area measurement is to set a minimum of
150 sq centimeters at one year of age. Any heifer measuring less
is culled, but no preference is given to heifers measuring larger.

If pelvic area is
being measured a reproductive tract
score can be determinded at the same time.
If the uterine horn is less than 20 mm diameter and the ovaries are the size of peanuts at 6 to 8 weeks prior to the start of breeding season,
the heifer is either too young, too thin or was implanted as a calf.
Prospective replacement heifers should never be implanted with
growth promotants as implantation is associated with fewer heifers
cycling and conceiving, especially younger heifers and heifers
implanted more than once. A reproductive tract score of 1 would
be assigned to that heifer. A 5 reproductive tract score has a
uterine horn diameter greater than 30mm with good tone and ovaries
the size of a large lima bean with follicles and a CL (corpus luteum formed from the follicle after a heat cycle). A score of 4 would have
uterine diameter of 30mm and and lima bean sized ovaries with follicles.
Heifers should have a 4 or 5 reproductive tract score 6-8 weeks
prior to breeding season.

Choose well when selecting replacement heifers. Pay attention
to thier development with feed and vaccinations. The heifers are
the future of the cowherd.

Beth Blevins, DVM, has practiced in the Ronan, Mt. area since

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