November 2010 Articles

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Continued from Selection and Management of Beef Replacement Heifers

Continued form Selection and Management of Beef Replacement Heifers Source: University of Arkansas
Management From Weaning to Breeding
The period between weaning and breeding is a very critical time for the long-term reproductive performance of replacement heifers. At weaning, heifers should be between 7 to 8 months of age and weigh 500+ pounds. It is very important to weigh the weaned heifer so that the weaning weight is known and not guessed. It is also recommended to determine the frame score of the replacement heifer. Frame score is a convenient way to describe the skeletal size of cattle. Hip height converted to frame score is a
measurement that helps determine mature body size. Larger-framed heifers tend to be heavier and be later maturing (puberty) compared to medium- and smallframed heifers. The recommended site for hip height measurement is a point directly over the hooks. The following table provides a conversion from hip height measures to frame score based on age of the heifers.
Table 3. Hip height (inches), frame score and mature
weight for heifers.
Age Frame Score (hip height in inches)
Months 3 4 5 6 7
6 38.2 40.3 42.3 44.4 46.5
7 39.2 41.2 43.3 45.3 47.4
8 40.1 42.1 44.1 46.2 48.2
9 40.9 42.9 44.9 47.0 49.0
Estimated
Mature 900 lb 1,000 lb 1,100 lb 1,200 lb 1,300 lb

Weight
Frame scores provide an estimate of a heifer’s mature body weight. For example, a 7-month-old heifer with a hip height of 43.3 inches would be a frame score 5 and expected to weigh 1,100 pounds when mature. When selecting replacement heifers at weaning time, it is recommended not to select heifers less than
frame score 4 or more than a frame score 6. Heifers on either end of the frame score scale will be either too small or too large for efficient production. Frame score 4, 5 and 6 heifers are moderate size and prove to be more efficient in most situations. The initial postweaning growing phase begins at the end of the weaning phase and continues to the time the heifers are exposed to the bull. The growth rate during this phase should be calculated to allow heifers to reach their target weight for breeding. The growth rate can be accelerated during this period so that heifers behind in development can catch up, but the gains should not exceed 2 lbs per day. The most critical point is that heifers be at the desired weight for breeding, which is approximately 65% of their mature weight. There are three ways to determine the mature weight of a heifer. One method is to use the frame score system described in Table 3. A second method is to use published breed averages as listed in Table 4, and a third method is to use the weight of the heifer’s dam. Table 4. Weight needed to reach puberty by breed composition.
Breed or Breed Type Weight (lbs)
Angus 650
Brangus 700
Charolais 775
Hereford 700
Charolais x British 775
Simmental Crosses 700
Limousin Crosses 700
Gelbvieh Crosses 650
Brahman x British 750
Puberty is a function of both weight and age. Some of the larger framed breeds or breed types may need to be older to reach puberty compared to the more moderate framed breed or breed types. A heifer could obtain the weight necessary for puberty but be too young for puberty to be expressed. Brahman influenced heifers may have a slower rate of sexual maturity compared to
non-Brahman breeds. Generally, the average daily gain of heifers will need to be about 1.25 lbs per day from weaning to first breeding, and while this can be achieved with pasture alone, typical hay or average pasture quality will require supplementation. The supplement may need to provide protein, energy or both,
and hay should be analyzed to determine which is needed and in what amounts. It is also recommended to weigh the growing heifers every 30 to 45 days to determine if their gain is satisfactory.
If the heifers are gaining too much or too little, supplementation can be adjusted. To ensure that all heifers reach the weights
recommended before the breeding season, they should be fed separately from the cow herd and, if possible, sorted into feeding groups according to size and/or age at weaning. Lighter weight heifers will require a higher concentrate ration for the faster rate of gain necessary to reach the desired weights than larger, heavier heifers. It is also important to have enough bunk space so that all heifers have an equal opportunity to the supplement. The following growing heifer example illustrates how to use the target weight concept to determine the desired rate of gain needed for heifer development.
Table 5. Growing heifer example.
Situation at Weaning:
Heifer age: 7 months or 210 days
Average weaning weight: 500 lbs.
Average frame score: 5
Weaning date: October 1
Target Estimates:
Target breeding date: April 1
Target breeding weight: 715 lb (1,100 pounds times
65%)
Calculations:
Gain needed: 715 minus 500 = 215 lb
Feeding period: 180 days (Oct 1 to April 1)
Average Daily Gain: 215 divided by 180 days =
1.19 lb/day
Once the forage is analyzed, a cost-effective supplement can be formulated to achieve the desired rate of gain. It is important to weigh heifers throughout the growing period to measure progress, and supplements can be adjusted accordingly. Another advantage of weighing heifers is it helps identify those heifers exhibiting poor growth. Those heifers that are not gaining well will not reach target weight and will probably not become pregnant or become pregnant late in the breeding period. The sooner poor growing heifers are identified and culled, the more efficient the growing program becomes. It is not unusual for heifers to have no weight gain or a loss of weight in the early spring. When the new young tender grass growth occurs, heifers would prefer to consume the young tender grass rather than harvested hay. Although the young tender grass is higher in quality, the quantity during this time of year is limited. This results in a reduced weight gain during this period. The reduction in weight gain is
short term and is quickly overcome.