This tutorial will help you understand the concepts behind switching from making bunk calls on an as fed basis to a dry matter basis. Although it is different, making bunk calls on a dry matter per head basis is much easier.
When feeding it is important to realize that the moisture in the feed does not really affect growth. So when you are targeting a specific amount of growth you need to make sure that the dry matter portion of a ration stays balanced and consistent. But the reality is that the moisture content of the ingredients will change over time.
Look at the picture on the left in the Dry Matter Tutorial window. It represents a ration, shown on an as fed basis so you can see the moisture content of each ingredient. This moisture is shown on the y-axis. The yellow is the dry matter content and the blue is the water. You can drag the horizontal lines to change the moisture content of each ingredient. The x-axis shows the percentage of the ration that each ingredient makes up. You can grab the vertical line separating ingredients and drag it left or right to change the ration composition.
At the top of this window you can see controls to change the ration, bunk call, head count, and weight of animals is a pretend pen. To the right of the picture you will see a load and other information. You can get an idea of how these values need to change when you change the ration, bunk call, head count, or weight. They will also change when you change the composition of the ration or the moisture content of ingredients by dragging the lines in the picture.
If you are used to making bunk calls on a per pen basis, you will appreciate how much easier and consistent it is to make bunk calls on a per head basis. This is simply because you don't have to change the bunk call when the pen count changes. To see this, drag the head count slider above to change the number of head in the pen. Notice that the As Fed Call/Pen must change where the regular bunk call can remain constant. If you made bunk calls on a per pen basis you would have to recalculate the bunk call each time the head count changed. With Fusion and per head bunk calls, you don't have to worry about this. Fusion will take care of adjusting the load and pen delivery amounts automatically when the head count changes.
Try changing the normal bunk call by moving the slider. Notice that as you do, the resulting load and other information all change. This is because a dry matter per head based bunk call drives everything else.
For example, let's say the moisture content of an ingredient changes. Change the moisture content of one of the ingredients by dragging in the picture. Notice as you do both as fed calls have to change but the normal bunk call does not change. If you were making as fed bunk calls, you would have to recalculate them each time an ingredient's moisture content changed. But with a dry matter bunk call, Fusion can do this automatically for you.
The same is true if the composition of a ration changes. Try changing this aspect of the picture and watch the as fed bunk calls. Again, they must change to reflect the difference but the normal bunk call does not. You can even switch to a different ration and notice the same thing. The as fed bunk calls will have to change, but the normal bunk call does not change.
Following are three rules of thumb to help you as you learn to think on a dry matter per head basis with bunk calls. Keep these in mind as you play with the ration and sliders and watch the DMI%BW value change.
In the Bunk Call/Feed Delivery window where you make bunk calls, Fusion shows the DMI%BW value as you change the bunk call so you can use these rules of thumb until are comfortable thinking on a dry matter basis. (It can also shows the equivalent as fed values as well if set up this way in the Preferences window.)
Although making bunk calls on a dry matter per head basis may seem uncomfortable at first, it will definitely be easier once you get used to it. Playing around with this window can help you get a feel for what values depend on other values and recognize that the normal (dry matter per head) bunk call is what drives everything else.
You can open this window by going to Fusion Feed → Feeding → Dry Matter Tutorial.