The accuracy of laboratorial methods to estimate the digestibility and energetic value of beef cattle diets was evaluated. Experimental diets were isonitrogenous and composed by corn silage, and 25, 40, 55, or 70% of concentrate. Digestibility values measured in vivo were compared to those obtained in situ, in vitro, and in vitro/gases assays, as well to values estimated from mathematical equations based on the chemical composition of diets. The in vivo assay was carried out using four cattle in a Latin Square experimental design. Four animals were used for in situ assay and four runs were carried out for in vitro assays. Significant interaction of method vs. diet was not observed. As single indicators, degradation rates calculated from in situ and in vitro/gas assays were not accurate to estimate the nutritive value of feeds. Among all tested methods, the in vitro assay was the most accurate to estimate the digestibility of diets. Weiss equation overestimated the nutritional value of diets by overestimated fiber digestibility and by underestimated fecal endogenous excretion. However, it was more accurate than McDowell equations.
ruminant; digestibility; equations; in situ; in vitro; in vivo
