Cindy:
There is a difference between a fixed formula ration and a fixed ingredient listing ration. I would not want a fixed formula ration because of changes in the nutrition found in feed ingredients. On the other hand, having a fixed feed ingredient feed allows the feed manufacture adjust...
You really don't want a fixed formula since the nutrient content of the ingredients change over time, especially from crop year to crop year. Also having a fixed formula can have dramatic effects on the price of the feed as ingredient prices change.