When a feed is abruptly switched, the bacterial population doesn't have time to adapt to the new mix of ingredients. One kind of bug may multiply quickly and start producing acid or gas which can cause pain and discomfort to the animal. Now we have one type of bug dominating and the bacterial population is out of balance. This doesn't have to happen. By adding new feeds very slowly to the diet, all the bugs will have time to adapt to the new ingredients and the bacterial population stays in balance.
Balanced bugs mean no excess acid or gas and no upset stomachs.
Also remember you should Not Increase Total Feed During the Adaptation Period. If your animal is growing or working hard and losing weight, you can begin to slowly increase the total amount of daily feed intake. These guidelines may seem very slow, but if they are followed, the digestive tract bugs should stay balanced, your animal will stay happy and healthy and you will save time in the long run.