Maintenance
of a quality cow herd requires a constant input of new breeding
females. With cattle prices at the levels they are currently however,
many producers are electing to hold off retaining females in order
to market more head and take advantage of the profit opportunities.
Nonetheless, while many ranches will buy many of the replacement
cows and heifers they need, a sound on-farm, heifer selection
and development program is very important to ongoing ranch management
and operation. It is estimated that about 30 percent of the heifer
calves produced in the U. S. are retained and developed for cowherd
replacements. Costs associated with heifer development represent
a significant up-front investment. Additionally, management of
the heifer during the development period can significantly affect
her lifetime productivity and must be carefully planned.
Research has shown us that heifers that calve early in their
first calving season continue to calve early in subsequent calving
seasons and wean heavier calves throughout their lifetime compared
to heifers that calve later in their first calving season. Therefore,
it is very important that heifers are managed to enhance productivity
and control costs.
The period from the time the heifer calf is weaned to the
time she is bred is critically important in replacement heifer
development. As a producer, your goals should include getting
heifers bred early, minimizing calving difficulties, weaning
acceptable calves, and having the heifer stay in the herd for
a long, productive life.
Preweaning Management
As with any growing calf, prior to weaning, the replacement
heifer is largely dependent on the dam to provide nourishment
and care. However, there are some management practices which
can impact the future productivity of heifers during this period.
If possible, heifers should be individually identified to allow
producers to base selection upon actual records of birth weight
and weaning weight. Other considerations include:
1) Creep feeding. Data regarding creep feeding
replacement heifers is controversial. In some instances, creep
feeding replacement heifers can result in reduced performance
when those heifers enter the cow herd. The problem is more prevalent
when the cows are good milkers and creep feed is consumed at
a rate of 3 to 6 pounds per day. Apparently, excess fat can
be deposited in the mammary tissue, resulting in lower milk
production potential and lower productivity when heifers enter
the cow herd.
In contrast, an extensive survey conducted by the American
Simmental Association and Montana State University indicated
no reduction in subsequent performance when creep fed heifers
were compared to non-creep fed heifers.
2) Selection. Traditionally, the biggest
heifers at weaning have been retained for replacements. This
method is simple and straightforward. This selection method
is not necessarily bad, since older heifers from earlier calving,
heavier milking dams with good growth potential would be selected.
However, care must be taken to avoid selecting heifers which
may be overly fat. This can lead to reduced milk production,
or may have some endocrine imbalance leading to reduced fertility.
This method may also result in the gradual increase in mature
cow size, which at some point leads to herd production inefficiencies.
A strict selection process should be developed to select replacement
heifers. This process should use available weight and performance
records as well as visual appraisal. Select heifers from sires
that transmit desired milk production and mature size and have
demonstrated early sexual maturity. From this pool keep those
heifers of desired body type and frame size which are most likely
to breed early, calve without difficulty, and remain sound with
minimal inputs.
Age at Puberty
In order for a heifer to calve at 22 to 24 months of age,
she must reach puberty by 12 to 14 months of age. Table 1 shows
the breed group averages for age and weight at puberty based
on data from the US Meat Animal Research Center.
Breeds and breed types vary with respect to age at puberty.
In addition, sire selection within a breed also plays a role
in determining age and weight at puberty. Age and weight at
puberty are moderately to highly heritable traits. This means
that producers can use selection to improve these traits within
a given herd.
An easy method of selection for age at puberty in replacement
heifers is to select daughters of bulls with large scrotal circumference.
An interesting correlation, in general, bulls with larger scrotal
circumferences have daughters that reach puberty earlier.
Another related study at the University of Nebraska indicates
that exposing heifers (from weaning to breeding) to surgically
altered (gomer) bulls can reduce age at puberty by 40 days and
increase the number of heifers bred during the first 21 days
of the breeding season.
Target Breeding Weights
Heifers that breed and calve early their first year have been
shown to have an advantage in lifetime production. This is in
addition to a reduction in overall production costs to the initial
calving. For early breeding to occur, heifers must be cycling
at the start of the breeding season. Furthermore, conception
is greatly improved by breeding after several heat cycles compared
to the first estrus. Therefore, heifers should be cycling 60
days prior to breeding or by about 12 months of age.
The level of nutrition the heifer receives the first winter
following weaning will influence her rate of development, weight
gain, and the age and weight at which she reaches puberty. Heifers
fed for a higher rate of gain will be heavier and younger at
puberty. Low rates of gain will delay puberty, but heifers will
reach puberty at a lower weight. The fact that weight has such
an important impact on sexual development allows use of a simple
nutritional management concept known as target weight. A heifer's
target weight is the minimum weight she should achieve by the
time she is exposed for breeding.
Current target weight recommendations call for heifers to
weigh 65 percent of their estimated mature weight at the time
of breeding. Mature weight of heifers can be estimated from
frame scores determined by measuring height at the hip or from
weights of similar cows in the herd.
Feeding management is especially important at this time. In
addition to greater feed costs, overfeeding heifers may also
contribute to decreased productivity. The period from about
three to nine months of age is critical to mammary growth in
heifers. Both inadequate nutrition and overfeeding in this period
have been shown to result in reduced milk production.
Target gains will vary depending on weaning weights, frame
size, breed type, and length of the backgrounding feeding period.
Typical gain targets from weaning to breeding are 1.25 to 1.5
lbs per day for British breed type heifers and 1.5 to 1.75 lbs
per day for Continental breed types. Research suggests that
the rate of gain in the development period does not need to
be constant as long as the target weight is reached. In fact,
some research identifies advantages to developing heifers in
stages of reduced energy and gain followed by periods of compensatory
growth. A slight reduction in feed expenses has been shown for
heifers developed at fairly slow rates of gain early followed
by a period of accelerated growth just prior to breeding.
Feeding and Nutrition
It is relatively easy to feed heifers from weaning to breeding
to accomplish targeted moderate rates of gain with fairly simple
rations. Replacement heifers have nutrient requirements which
differ from the rest of the cow herd; consequently, they should
be fed and managed separately.
Heifers are commonly developed most economically on high forage
rations supplemented with grains and grain by-products, protein
concentrates, and minerals as needed to meet their needs and
gain target. Modest levels of gain can be achieved solely on
high quality roughage fed on a free-choice basis.
In addition, it is important to understand the composition
and quality of feeds to be fed. Forages, in particular, vary
considerably in level of protein and energy and should be analyzed
in order to accurately balance rations. High quality hays are
those with over 12 percent crude protein and 58 percent TDN.
Hays with crude protein values between 8 and 11 percent and
TDN in the mid 50s would be considered average quality hays.
Hay with less than 8 percent crude protein and 52 percent TDN
would be considered low quality forage.
Insufficient energy intake which results in poor growth can
have negative effects on breeding performance of heifers as
yearlings and on their subsequent performance in the cowherd.
If large groups of heifers will be developed, producers should
consider splitting the heifers into two or more feeding groups
(based on weight). This will allow more precise feeding of each
group based on necessary target breeding weights and daily gains.
Proper feeding and nutrition of developing heifers is very
important. What are the costs of nutritional mismanagement?
Here are a few of the implications:
1. Increased age at puberty
2. Lower conception rates
3. Greater degree of calving difficulty
4. Increased calf morbidity and mortality
5. Calves born later in the calving season
6. Lighter weaning weights
7. First calf heifers with poor reproductive performance during
rebreeding
8. Later rebreeding of first calf heifers
9. Reductions in lifetime productivity
10. Increased rate of culling
Conclusions
Building a quality cow herd requires significant investments
of time, money and above all, dedication. It is up to the producer
to determine which methods he wishes to follow and implement
the appropriate strategies to achieve the desired goals which
is a cow herd that is profitable today and tomorrow.
Dr. Steve Blezinger is a nutritional and management consultant
with an office in Sulphur Springs, TX. He can be reached at
667 CR 4711 Sulphur Springs, TX 75482, by phone at (903) 885-7992
or by e-mail at [email protected].
