Using Ndf Digestibility Information in Dairy Cattle Feeding Programs

Dry matter intake (DMI) is related to dietary NDF content (Mertens, 1987) and in vitro NDF digestibility (NDFD, % of NDF; Oba and Allen, 1999). The NRC (2001) summative energy equation is based on fiber digestibility calculated using lignin. Whole-plant lignin content was found to have a strong negative relationship with in-vitro NDFD within comparisons of brown midrib (bm3) hybrids to isogenic counterparts (Oba and Allen, 1999b). However, stover NDF and lignin contents increase while NDFD decreases with progressive maturity, while whole-plant NDF and lignin contents are constant or decline as the grain proportion increases (Russell et al., 1992; Hunt et al., 1989). This my partially explain why for 534 corn silage samples, NDFD calculated using lignin according to NRC (2001) accounted for only 14% of in vitro NDFD variation (Schwab and Shaver, unpublished). Michigan State workers (Oba and Allen, 2005; Allen and Oba, 1996; M. S. Allen, personal communication, 2003 Tri-State Nutr. Conf. Pre-Symp.) reported that lignin (% of NDF) explained only half or less of the variation for corn silage in vitro NDFD. These observations coupled with the NRC (2001) suggestion that in vitro NDFD measurements could be used directly in the NRC model led us to implement in vitro NDFD rather than lignin-calculated NDF digestibility in our milk per ton model for corn silage evaluation (MILK2000; Schwab et al., 2003).