How Many Replacement Heifers Should You Keep Each Year?
Matching the number of cattle to the grass and
feed resources on the ranch is a constant challenge for any cow-calf producer. Also producers strive to
maintain cow numbers to match their marketing plans for the long term changes in the cattle cycle. Therefore
it is a constant struggle to evaluate the number of replacement heifers that must be developed or purchased to
bring into the herd each year. As a starting place in the effort to answer this question, it is important to
look at the “average” cow herd to understand how many cows are in each age category. Dr. Kris Ringwall,
director of the Dickinson, North Dakota Research and Extension Center recently reported on the average number of
cows in their research herd by age group for the last 20 years. The following graph depicts the “average”
percent of cows in this herd by age group.
The above graph indicates that the typical herd will, “on the average”, introduce
17% new first calf heifers each year. Stated another way, if 100 cows are expected to produce a calf each
year, 17 of them will be having their first baby. Therefore this gives us a starting point in choosing how
many heifers we need to save each year.
Next, we must predict the percentage of heifers that enter a breeding
season that will be come pregnant. The prediction is made primarily upon the nutritional growing program that
the heifers receive between weaning and breeding. Researchers many years ago, found that only half of heifers
that reached 55% of their eventual mature weight were cycling by the time they entered their first breeding
season. If these heifers were exposed to a bull for a limited number of days (45-70), not all would have a
chance to become pregnant during that breeding season. Therefore, it would be necessary to keep an additional
50% more heifers just to make certain that enough bred heifers were available to go into the herd. However if
the heifers were grown at a more rapid rate and weighed 65% of their eventual mature weight, then 90% of them would
be cycling at the start of the breeding season and a much higher pregnancy rate would be the result.
Even in the very best scenarios, some heifers will be difficult or impossible to
breed. Most extension specialists and researchers write about the need to always expose at least 10% more
heifers than you need even when they are grown properly and all weigh at least 65% of the expected mature
The need to properly estimate the expected mature weight is important in understanding
heifer growing programs. Cattle type and mature size has increased over the last half century.
Rules of thumb that apply to 1000 pound mature cows very likely do not apply to your herd. Watch sale weights
of culled mature cows from your herd to better estimate the needed size and weights for heifers in your
program. Most commercial herds have cows that average about 1150 pounds. This requires that the heifers
from these cows must weigh at least 747 pounds at the start of their first breeding season to expect a high
percentage to be cycling when you turn in the bulls.
This short article is just a STARTING PLACE in the decision to determine the number of
heifers needed for replacements. Ranchers must keep in mind the over-riding need to understand where they are
in the cattle cycle, grazing capacity and many other variables in order to make their best