The impact of fiber digestion on dairy nutrition is complex, and all the measurements of fiber digestion listed on the forage report add to the confusion. Understanding fiber digestion requires knowledge of what actually happens in the cow (in vivo) as well as why and how we try to estimate it in the laboratory (in vitro).

Forage is an important ingredient in dairy cattle rations. However, it can be difficult to achieve high intake levels with certain forage-based diets. We have long recognized that NDF digestibility influences intake. In fact, researchers in 1999 made the observation that a one-unit increase in NDF digestibility (NDFd) is associated with 0.37-pound increase in dry matter (DM) intake and 0.55-pound increase in 4 percent fat-corrected milk.