PSXII-22 Ruminal in situ dry matter and starch degradability in grain sorghum silage, as affected by processing and storage time

Abstract Our previous studies showed that processing sorghum silage at harvest and storing for approximately 150 d, improved average daily gain (ADG), feed efficiency (FE) and apparent total tract digestibility (ATTD) of starch when included as the basal ingredient in diets fed to growing Angus heifers. However, differences in animal performance and nutrient digestibility disappeared when the same sorghum silage was fed again after 1 yr of storage. An experiment was performed to evaluate the effects of kernel processing and storage time on ruminal in situ degradability of sorghum silage (SS). A grain sorghum (ADV2450IG, Advanta seeds, Irving, TX) was harvested (Claas Jaguar 930, Harsewinkel, Germany) at the late-dough stage of grain maturity. Treatments were applied at harvest and consisted of sorghum berry processing (PRO) with a specific SS kernel processor (196 mm rolls of 125 teeth each, 40% speed differential, 1.1 mm roll gap), or not processed at all (NPR). Silage was chopped at 15 mm theoretical length of cut and ensiled in polyethylene ag bags (60 m long and 2.74 m diameter), for 455 d. Samples were taken from each treatment on d 0, 66, 112, 157, 202, 246, 291, 336, 381, 426, and 455 and were kept frozen until analyzed. Samples were dried but not ground, to avoid affecting treatments. Ruminal in situ degradability of dry matter (DM) and starch was determined by incubating nylon bags for 24 h in duplicate, in the rumen of four ruminally cannulated steers consuming a corn silage-based diet. Data were analyzed as a randomized block design with repeated measures. The fixed effect of treatment, day and their interaction were included in the model and the repeated subject was considered the animal within treatment. A storage day × treatment interaction was detected for in situ DM degradability (P < 0.001). The PRO treatment increased (P < 0.05) in situ DM degradability at 66 and 202 d of storage and tended to increase it (P = 0.07) at 157 and 291 d of storage. An effect of storage day (P < 0.05) was observed for in situ starch degradability and because there was no interaction with treatment (P = 0.43), treatments means were compared across storage days. No differences were detected in ruminal in situ digestibility of DM or starch when silage was stored for 202 d, when compared with d 0 (P = 0.43), while starch degradability increased when silage was stored for 202 and 291 d (P < 0.03). At 381 d of storage, no differences were detected for starch degradability when compared with d 0. In conclusion, berry processing of sorghum when harvested for silage, increased ruminal in situ DM degradability. However, those differences disappear after more than 200 d of storage, in agreement with animal performance data previously reported by our group.