Effects of Fibrolytic Enzyme on in-Vitro True Digestibility of By-Products Commonly Fed to Cattle

In vitro true digestibility of DM, OM, NDF, and ADF with and without inclusion of a fibrolytic enzymes were evaluated in 12 byproducts. Ruminal fluid inoculum was collected from donors (ruminally cannulated beef steers; n = 4; BW = 463 ± 53 kg) during 4 periods (each period consisted in one in vitro batch [experimental unit]). Donors were fed forage-based diets (high and low quality) for 21 d prior collections (each in vitro batch was inoculated with a mixture of rumen fluid from both high and low quality diet donors). Incubations followed a randomized complete block design (block = in vitro batch). Substrates consisted of: corn cobs (CC), intact sorghum grain (ISG), wheat straw (WHST), cotton burrs (CTBR), corn stalks (CSTK), cotton seed hulls (CSH), grape pomace (GRPM), soybean hulls (SBH), high-quality alfalfa (ALFH), low-quality alfalfa (ALFL), sorghum stalks (SRST), and sorghum dry distillers’ grains (SDDGS). Samples were incubated in DAISYII Incubator (Ankom Technology, Macedon, NY) with fibrolytic enzyme (0.75 µl/g of substrate DM; ABVista, United Kingdom) within jar (24 bag plus blank). Quadruplicate samples were incubated according to unit instructions. Following 48-h incubations, analyses NDF, ADF, and ash were performed on bags in sequence. Data were analyzed using the GLIMMIX procedures of SAS, with enzyme, substrate type, and interactions as fixed effect and in vitro batch as random. An enzyme treatment × substrate interaction resulted in a 13.2% increase (P < 0.01) in IVTDMD of ISG as well an observed tendency (P = 0.10) for greater digestion in CSTK. Similarly, IVTOMD of ISG was enhanced (P < 0.01) with addition of enzyme. Sorghum grain also produced an enzyme treatment × ingredient interaction associated with NDF digestibility in which inclusion on enzyme increased (P < 0.01) digestion by 16.35% relative to no enzyme. Regardless of substrate type, addition of enzyme increased (P < 0.01) disappearance of ADF by approximately 13.6%. Ingredient differences (P < 0.01) associated with ADF digestibility resulted in SBHS being the highest (71.78%) whereas CTBR, CSHS, and GRPM had the lowest values (≤ 24.60%). Fibrolytic enzymes positively affected fiber digestion of commonly fed roughage sources in cattle diets, and might have additional benefit when used on sorghum grain-based diets.