Effects of Pentacyclic Triterpenes on in Vitro Fermentation of Bahiagrass Hay and a High-Grain Substrate

Triterpenes are the most representative group of phytochemicals, comprising more than 20,000 recognized molecules. The diversity of triterpenes is highly associated with their broad range of pharmacological effects. Previous studies have demonstrated their anti-microbial potential. Our objective was to determine potential effects of pentacyclic triterpenes (TT) on in vitro batch culture fermentation of bahiagrass hay and a high-grain substrate. A randomized complete block design was used to determine the effects of increasing concentrations of the following TT types: oleanolic acid (OA), ursolic acid (UA) and malsinic acid (MAL) on in vitro fermentation of bahiagrass hay (BGH) or a high-grain substrate (HG) comprised of 43% soybean hulls pellets, 42% corn gluten feed pellets, and 15% peanut hulls (DM basis). Treatments were arranged as a 4 × 3 factorial with 4 doses (0, 4, 25 and 100 mg/L of incubation volume) for each of the 3 TT types. Four ruminally cannulated crossbred steers (362 ± 30 kg BW) were used as ruminal fluid donors. Two steers were fed HG ad libitum, while the other two steers were fed BGH ad libitum for at least 14 d prior to the first incubation day. Each replicate d, 125-mL serum bottles containing 50 mL of a 4:1 buffer:ruminal fluid inoculum and 0.63 g of BGH substrate (DM basis) were incubated for 48 h, and a 2:1 buffer:ruminal fluid inoculum and 0.63 g of HG substrate (DM basis) were incubated for 24 h. Three d (block) of incubation were performed. In vitro OM digestibility (IVOMD) was determined in a separate set of tubes. Data were analyzed using PROC MIXED of SAS with the fixed effect of treatment, and random effect of incubation day. No effect was observed (P > 0.05) on total gas production, IVOMD, NH₃-N concentration and H₂S production. There was no effect (P > 0.05) of any TT types or doses on concentrations or molar proportions of VFA. No effect (P > 0.05) of TT type or dose were observed on acetate:propionate ratio (A:P). In conclusion, the acid form of the pentacyclic triterpenes did not affect ruminal fermentation of either substrate. Future studies should focus on increasing the solubility of these pentacyclic triterpenes by using a sodium salt.