Formulating with weight constraint <> 1

It is sometimes useful to formulate a given feed at a nutrient density different from that in the original feed. Instead of adjusting all the essential nutrients such that they remain in the same proportion to ME as in the base feed, a special feature in WinFeed allows the user to change the nutrient density without altering any of these nutrient concentrations. This is done by altering the value of the weight constraint.

The default upper and lower bounds of the Weight “nutrient” are 1.0. A feed in which the nutrients are supplied at least cost per unit of energy may be obtained by setting a range of weights, say, from 0.95 to 1.05, and then formulating. Alternatively, the weight bound may be set at a value lower than 1.0 for a higher density feed, or higher than 1.0 for a feed with a lower nutrient density than in the original feed

If the resulting weight is not 1.0, then essentially the sum of the ingredients is not 100%. However WinFeed recalculates the ingredient percentages so that they do add up to 100%, and you can see the actual nutrient concentration of the nutrients in the feed by clicking on the Weight=1 button that is only visible if the formulated value of weight does not equal 1. This will show the actual nutrient concentrations in the feed even though some will break the bounds that were set. By clicking on this button it is possible to see either the unadjusted or adjusted nutrient and ingredient values. The unadjusted ingredient solution will show what the ingredient values were that added up to the formulated weight (these values will not add up to 100). In the example below, weight was set with both upper and lower bounds equal to 0.9. These are the unadjusted figures, with the ingredients totalling 90.

By clicking on the Weight=1 button, the following adjusted values are shown, with the ingredient contents adding to 100%.

In this way it is possible to formulate a range of feeds differing in nutrient density – without having to alter all the nutrient concentrations each time (remember that nutrient density refers to the concentration of all nutrients in the feed). To produce a feed that is higher in nutrient density than the control (=100), the nutrients should be made to “fit into a smaller bag”, so the weight should be made smaller (e.g. 0.90). All the ingredients and the nutrients in the final solution should be multiplied by 1/0.9 to make the mixture total 100 percent. This will produce a feed with a nutrient density equal to 1/0.9 of the original density.

Similarly, by setting a weight of 1.2, and multiplying all the ingredient and nutrient concentrations in the final mixture by 1/1.2, a less dense feed will be produced. In both cases the nutrients will remain in perfect balance. In this way a range of feeds can be formulated, with weight varying between, say, 0.9 and 1.2 in ten steps; the cost of the different nutrient densities can be calculated, which is the first step in calculating the optimum nutrient density of broiler feeds.