The Samuel Roberts Noble Foundation, Inc.
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Supplement Conversion Ratio

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Most cattle producers are familiar with the term "feed conversion." It is simply the amount of feed an animal consumes as compared to the amount of body weight gained, expressed as a ratio. Feed conversion ratios in the neighborhood of 6:1 (6 lbs of feed per pound of gain) are common in modern beef cattle feedlots. Stocker cattle producers are also interested in feed conversion, but the calculation is a little different. When feeding stockers that are grazing forage, we are most interested in "supplement conversion," which is the amount of supplement fed compared to the amount of additional gain the cattle exhibit. This additional gain is over and above what the cattle would gain from the forage alone, without the supplement. Supplement conversion is hard for a producer to measure, because they usually don't have a control group of non-supplemented animals.

Stocker producers typically must rely on research experiments to help them estimate supplement conversion in different situations. There are a multitude of variables that can affect supplement conversion, making it difficult to confidently predict. Furthermore, there is limited research information available concerning the conversion of byproducts in these different situations. For this reason, the Noble Foundation has begun to conduct a few experiments to address this.

In the summer of 2008, Noble Foundation intern Jessica Evans conducted a 58-day research project at our Oswalt Road Ranch where heifers were fed free-choice medium quality grass hay. In addition to the hay, some heifers were also supplemented with about 10 lbs of either corn dried distillers grains (DDG) or soybean hulls (SBH) three days per week. This level of supplementation was equivalent to feeding 0.75 percent of the heifer's body weight per day. Another group of heifers served as controls and received no supplement. As you can see from Figure 1. Supplement conversion ratio of two byproducts when fed with freechoice medium quality hay." Figure 1, supplement conversion ratio of DDG was better than SBH (4.2:1 versus 5.6:1, respectively). In this experiment, both supplements were profitable to feed; however, DDG was more profitable than SBH even though the DDG cost more per ton. This exercise demonstrates the value of having good estimates of supplement conversion ratios when evaluating stocker programs. Good, controlled research is the best way to get those estimates.

Corn dried distillers grains and soybean hulls
A Noble Foundation research project evaluated heifers being fed free-choice medium quality grass hay while also being supplemented with either corn dried distillers grains (above, left) or soybean hulls (above, right). Both supplements were profitable to feed, but dried distillers grain had better conversion ratios.
Figure 1
Supplement conversion ratio of two byproducts when fed with freechoice medium quality hay.