Abstract
In one-carbon metabolism, methionine (Met) is methyl donor and folic acid (FA) is responsible for the transfer of methyl groups. Approximately 25 % of coated methionine (CMet) and coated folic acid (CFA) released in the rumen at 24 h of incubation. Therefore, the present study investigated the effects of CMet or/and CFA on growth performance, nutrient digestibility and rumen fermentation in bulls. Forty Simmental bulls, 464 ± 15.9 kg of body weight (BW), were blocked by BW and randomly assigned to four groups in a 2 × 2 factorial arrangement of treatment, with factors being CFA 0 or 6 mg FA/kg dietary dry matter (DM) and CMet 0 or 0.66 g Met/kg dietary DM. The experiment period was 81 days long with 20 days for adaptation and 61 days for data and sample collection. Dry matter intake increased (P = 0.001) with CFA or CMet addition. The CFA × CMet interaction was noticed on average daily gain (ADG; P = 0.001) and feed conversion ratio (FCR; P = 0.020); the improvements in ADG and FCR were greater for supplementing CMet in diets with CFA than in diets without CFA. The digestibility of DM, organic matter, neutral detergent fiber and acid detergent fiber increased (P < 0.050) with CFA or CMet addition. When CMet was supplemented, crude protein digestibility increased in CFA diets and was unchanged in diets without CFA. Ruminal pH decreased (P < 0.050), but total volatile fatty acid concentration increased (P < 0.050) with CFA or CMet addition. Acetate to propionate ratio was unchanged with CFA addition, but decreased (P = 0.039) with CMet addition. Rumen ammonia-N concentration decreased (P < 0.050) for either CFA or CMet addition. The activities of carboxymethyl cellulase, protease, α-amylase and cellobiase and populations of protozoa, total bacteria, fungi, dominant cellulolytic bacteria, Ruminobacter amylophilus and Butyrivibrio fibrisolvens increased (P < 0.050) with CFA or CMet supplementation. The CFA × CMet interaction was noticed on Ruminococcus albus population (P = 0.014); when CMet was supplemented, R. albus population increased for diets without CFA and was unchanged for diets with CFA. The activities of chymotrypsin in duodenum increased (P < 0.050) with CFA or CMet supplementation, and that of amylopsin and trypsin in ileum increased (P < 0.050) for bulls receiving CFA addition. The concentrations of glucose, albumin and urea nitrogen in blood were unchanged and homocysteine decreased (P < 0.050) with CFA or CMet supplementation. The CFA × CMet interaction was noticed on blood total protein concentration (P = 0.045); when CMet was added, blood total protein concentration increased for diets without CFA and was unchanged for diets with CFA. The concentration of folate in blood increased (P = 0.001) for CFA addition. The concentration of Met increased (P = 0.002) for CMet supplementation. The results indicated that dietary CFA or/and CMet supplementation improved growth performance, nutrient digestibility and rumen fermentation, and the greatest daily gain was observed for combined addition of CFA and CMet in bulls.
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