Effects of dietary soybean oil and coated folic acid on ruminal digestion kinetics, fermentation, microbial enzyme activity and bacterial abundance in Jinnan beef steers

This study was conducted to evaluate the effects of dietary soybean oil (SO) and coated folic acid (CFA) supplementation on ruminal digestion kinetics, fermentation, microbial enzyme activity and bacterial abundance in Jinnan beef steers. Eight ruminally cannulated Jinnan beef steers, averaging 15 months of age and 415 ± 5.6 kg of body weight (BW; Mean ± S.E.), were used in a replicated 4 × 4 Latin square design by a 2 × 2 factorial arrangement. Two levels of CFA (0 mg [FA-] or 115 mg per kg dietary DM [FA + ]) were supplemented to the diets without or with SO supplementation (0 g [SO−] or 30 g per kg dietary dry matter [DM] [SO + ]). Steers were fed a total mixed ration with ensiled corn forage to concentrate ratio of 50:50 on a DM basis. The SO × CFA interaction was observed for ruminal pH, total VFA concentration, molar proportions of acetate and propionate, the ratio of acetate to propionate and ammonia N content. Ruminal pH increased with SO supplementation, but decreased with CFA supplementation. Ruminal total VFA concentration, acetate molar proportion and acetate to propionate ratio decreased with SO supplementation, but increased with CFA supplementation. Ruminal ammonia-N content decreased with SO or CFA supplementation. No SO × CFA interaction was observed for nutrient degradability and digestibility. Degradability of neutral detergent fibre (NDF) and digestibility of DM, organic matter, NDF and acid detergent fibre decreased with SO supplementation, but increased with CFA supplementation. Degradability and digestibility of crude protein was not affected by SO supplementation, but increased with CFA supplementation. Pectinase activity was unaltered, whereas, other microbial enzyme activity, bacterial abundance and total PD excretion were affected by SO × CFA interaction. Activities of carboxymethyl-cellulase, cellobiase and xylanase and abundance of R. albus, R. flavefaciens, F. succinogenes and B. fibrisolvens decreased with SO supplementation, but increased with CFA supplementation. Activities of pectinase, α-amylase and protease as well as total bacterial abundance were not affected by SO supplementation, but increased with CFA supplementation. Total protozoal abundance decreased with SO supplementation, but was not affected by CFA supplementation. Abundance of P. ruminicola and R. amylophilus increased with SO or CFA supplementation. Total PD excretion increased with CFA supplementation, but decreased with SO supplementation. The results suggested that ruminal fermentation, NDF degradability, protozoal abundance, cellulolytic bacterial abundance and enzyme activity decreased with dietary SO supplementation, but increased with CFA supplementation. The supplementation of CFA in the SO diet could relieve the negative effects of SO on ruminal fermentation.