Indigestible internal markers for estimating the digestibility of feedlot beef cattle diets
The aim of the present work was to evaluate the adequacy of indigestible neutral detergent fiber (NDFi) and indigestible acid detergent fiber (ADFi) as internal markers to estimate the digestibilities of three feedlot beef cattle diets containing 60% corn silage and 40% concentrates, including sunflower meal and urea plus either 25% ground corn grain (GCG); 8.2% GCG, and 19.3% soybean hulls; or 8.5% GCG and 20% corn germ meal. Twenty-seven Nellore steers in confinement were distributed among the three treatments. The NDFi and ADFi percentages were quantified after 144h of in vitro incubation of ingredients, orts and faecal samples. The mean digestibilities of dry matter (59.9 vs 59.8%), crude protein (54.4 vs 54.3%), NDF (52.2 vs 51.8%) and ADF (40.4 vs 40.9%) estimated by NDFi and ADFi, respectively, were similar with no effect of ingredients used. It was concluded that the NDFi (18.9%) and ADFi (11.8%) concentrations of the 25% GCG diet were adequate to estimate the digestibility coefficients in diets with 40% of concentrate, independent of the inclusion of fiber-rich ingredients in partial substitution of ground corn.