Using Physically Adjusted NDF in Formulating Rations for Dairy Cows

Physically effective fiber (peNDF) is defined as that fraction of NDF that stimulates chewing activity and contributes to the floating mat of large particles in the rumen. A limitation of using peNDF is that it does not account for differences in rumen fermentability of nutrients, most notably rumen-degraded starch. The physically adjusted fiber (paNDF) system can be used to estimate TMR particle size and diet compositions needed to maintain target rumen conditions. The system is based on equations derived from a meta-analysis and estimates dietary physical and chemical characteristics required to maintain desired rumen conditions in lactating dairy cows. Effective fiber feeding recommendations are based upon diet ADF, NDF, forage NDF (INDF), starch, and proportion of the ration as forage or cottonseed, as well as particle size measures.