Hitting the Right Target Weight is Critical to Replacement Heifers

By John B. Hall, Extension Animal Scientist, Beef, Virginia Tech.
calendar icon 15 November 2006
clock icon 4 minute read

Replacement heifers need to be of sufficient weight and age to breed successfully. To insure heifers are developed properly from a nutrition and weight aspect, we have used the "Target Weight" concept. The Target Weight is the desired weight of all heifers by the start of the breeding season, and it is expressed as a percentage of mature weight. Recently, considerable discussion occurred on the optimum target weight. Is it 55%, 60% or 65% of mature weight?

Recently, many producers may have read articles discussing the success some western ranchers and researchers had with developing heifers to a lighter target weight to reduce development costs. But is what works in the Sandhills of Nebraska right for Virginia? Let's review some facts.

All cows are not the same. The cows in the Nebraska studies were composite cows of a moderate body size. In addition, the composite was of several breeds known for reaching puberty early and at light weights. Finally, the cattle were well adapted to the limited resources of the Nebraska Sandhills. So the heifers in the Nebraska study tend to reach puberty at a younger age and lower weights than our Virginia cattle.

In contrast, Virginia cow/calf producers have been pushing for increased growth and milk production. While this makes our VA cattle potentially more productive because of our abundant forage resources, it also makes them more "high octane" cattle. Genetically, Virginian cattle will partition nutrients towards growth which may delay puberty. In addition, our cattle are large with the average cow in VA herds weighing between 1250 lbs and 1350 lbs. The combination of larger mature size, and greater growth and milking ability means the typical Virginia heifer will be older and heavier at puberty.

Not all operations are the same. In a recent article, a large ranch reported on significant decreases in cost of heifer development when heifers were developed to only 55% of mature weight. Because of the large size of the operation, small reductions in feed costs add up to big savings. For our smaller VA herds, the savings will not be as great.

Also, this large ranch had the luxury of developing all or almost all of their heifer crop then keeping the ones that became pregnant and retaining ownership on the open heifers. While retaining ownership on open heifers is certainly an option for Virginia producers, most operations in our state will have to work with other producers to put together a truckload of heifers to go to the feedlot or use the VA Retained Ownership Program (VA ROP) to add-value to these heifers. Also, many smaller operations can't gamble on having too many open heifers.

The 65% target is right for Virginia. Due to the type of cattle we produce as well as the current value of replacement heifers, the target of 65% of mature weight should be the goal of producers developing replacement heifers in Virginia. This means a majority of the heifers should be at least 65% of their mature weight by the beginning of the breeding season.

So how can we use target weight in developing heifers? Producers can use this method to estimate the average daily gain (lbs./day) each heifer must achieve from weaning to breeding. First, find the average weight of the mature cows in Table 1. Then subtract the average heifer weaning weight from the target weight. The result is the average pounds each heifer needs to gain from weaning until breeding. If you divide the pounds needed to gain by the number of days until breeding, the result is the average daily gain needed from weaning until breeding.

Table 1. Target weights for heifers using 65% of mature weight
Mature Weight of Cows in Herd (lbs)
Target Weight for Heifers (lbs)
1150 750
1200 780
1250 815
1300 845
1350 875
1400 910

Here's an example. The average cow at Mostly Vertical Farm (MVF) is 1300 lbs. The average weaning weight of MVF heifers is 525 lbs. Heifers are weaned on November 1 and the breeding season starts on May 1. That makes the number days from weaning until breeding is 181, so let's call it 180. Here's the math.

From Table 1 the target weight is 845 lbs
845 lbs - 525 lbs = 320 lbs needed to gain by May 1
320 lbs / 180 days = 1.78 lbs per day gain

So the MVF heifers need to gain about 1.8 lbs per day from weaning until breeding. By working with his Extension Animal Science agent or local nutritionist the MVF manager can design a diet to meet the needs of these heifers using resources that are on the farm or locally available.

Research indicates that reaching the target weight is the most important nutritional factor in heifer development. Whether heifers gain at a steady rate from weaning until breeding or gain most of their weight in late fall or early spring does not appear to have dramatic effects on the percentage of heifers that become pregnant. There may be some limited effects on milk production, but if highly nutritious forage is available for calves between 4 months and weaning there is little impact on weaning weight.

Now is the time that producers with spring calving herds should determine the target weight their heifers need to reach by breeding and the average daily gain to get heifers to that goal.

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