128. In Vitro Incubation Times to Estimate the in Vivo Digestibility of Dry Matter and Organic Matter of Diets Based on Bolivian Giant Sorghum Silage Containing Different Levels of Concentrate

Abstract Digestibility is one of the main parameters used to define the nutritional value of a feed. Among the available methods, the in vivo approach is the most accurate for determining nutrient digestibility. However, it requires large amounts of feed and animals, making it costly and labor-intensive. This has encouraged the use of alternative methods, such as the in vitro technique, to evaluate feeds and complete diets. This study aimed to evaluate in vitro incubation times required to estimate in vivo digestibility of dry matter (DM) and organic matter (OM) in diets based on Bolivian Giant sorghum (AGRI-002E) silage with different concentrate levels. To determine in vivo digestibility, five non-castrated ruminal-cannulated Nellore bulls were used in a 5 × 5 Latin square design. For the in vitro method, ruminal inoculum was obtained from rumen-cannulated non-castrated F1 Nellore × Red Angus bulls. Five diets were evaluated with different concentrate inclusion levels: 0% (C0), 20% (C20), 40% (C40), 60% (C60), and 80% (C80) of diet DM. Animals were fed a 50:50 diet on a dry matter basis consisting of corn silage, ground corn, soybean meal, urea + ammonium sulfate, virginiamycin, and a mineral premix. About 0.5 g of each complete diet was placed in ANKOM® F57 filter bags and incubated in flasks within a TE-150 incubator (Tecnal Lab®). The incubation times were 0, 3, 6, 9, 12, 24, 48, 72, and 96 hours. For each diet, the mean, upper (UL), and lower (LL) limits of in vivo digestibility were estimated using 95% confidence intervals. The in vitro incubation time required to estimate in vivo digestibility was defined as the intersection between in vitro degradation curves and in vivo digestibility limits. Statistical analyses were performed using PROC NLIN in SAS. The means, LL, and UL of in vivo DM digestibility (g/kg) were: 532, 464, and 601 (C0); 579, 500, and 658 (C20); 646, 603, and 690 (C40); 690, 672, and 708 (C60); and 763, 729, and 797 (C80). For in vivo OM digestibility (g/kg), the means, LL, and UL were: 549, 484, and 615 (C0); 595, 513, and 677 (C20); 665, 624, and 707 (C40); 702, 682, and 722 (C60); and 773, 738, and 807 (C80). To estimate in vivo DM digestibility through the in vitro method, an average incubation time of 85 hours is recommended for C0. For both DM and OM of C40, an average of 82 hours is recommended, while for C60 and C80 diets, 49 hours are sufficient. In conclusion, in vivo digestibility of DM and OM can be estimated using different in vitro ruminal incubation times for diets based on Bolivian Giant sorghum (AGRI-002E) silage with varying concentrate levels.