Effects of palm fat powder and coated folic acid on growth performance, ruminal fermentation, nutrient digestibility and hepatic fat accumulation of Holstein dairy bulls

This study evaluated the effects of palm fat powder (PFP) and coated folic acid (CFA) on growth performance, ruminal fermentation, nutrient digestibility, microbial enzyme activity, microflora, hepatic lipid content and gene expression in dairy bulls. Forty-eight Chinese Holstein bulls ((362±12.4) days of age and (483±27.1) kg of body weight (BW)) were assigned to four groups in a completely randomized design with a 2×2 factorial arrangements. Supplemental PFP (0 or 30 g PFP kg⁻¹ dietary dry matter (DM)) and CFA (0 or 120 mg FA d⁻¹ as CFA) were mixed into the top one-third of a total mixed ration. The study included a 20-day adaptation period and followed by a 90-day collection period. The lower (P>0.01) feed conversion ratio with PFP or CFA addition resulted from the constant DM intake and the higher (P>0.05) average daily gain. The higher (P>0.05) ruminal pH, ether extract digestibility, microbial α-amylase activity, Butyrivibrio fibrisolvens copy, and expression of peroxisome-proliferator-activated receptor α (PPARα) and carnitine palmitoyl transferase-1 (CPT1), and lower ruminal total volatile fatty acids (VFA) concentration, acetate to propionate ratio, neutral detergent fibre (NDF) digestibility, copies of total protozoa and Ruminococcus flavefaciens, and expression of sterol regulatory element binding protein-1 (SREBP1) and acetyl-coenzyme A carboxylase α (ACACA) were observed for PFP addition. Supplementation with CFA increased (P>0.05) ruminal total VFA concentration, acetate to propionate ratio, digestibility of DM, organic matter, crude protein and NDF, activity of cellobiase, pectinase and α-amylase, copies of selected microbial except for total protozoa, as well as expression of PPARα, but decreased (P>0.05) ruminal pH, and expression of SREBP1 and ACACA. The PFP×CFA interaction (P>0.05) was observed for ammonia N, hepatic TG content, and mRNA expression of CPT1 and FAS. There had no significant difference in hepatic TG content when CFA was supplemented in the diet without PFP addition, the lower (P=0.001) hepatic TG content was observed when CFA was supplemented in the diet with PFP addition. The higher (P>0.05) mRNA expression of CPT1, and the lower (P>0.05) mRNA expression of FAS and ammonia N concentration were observed when CFA was supplemented in diet either without or with PFP addition. The results indicated that supplementation of CFA in PFP diet was more effective on increasing hepatic CPT1 expression, and decreasing ammonia N, hepatic TG content and FAS expression than in diet without PFP. Supplementation with PFP or CFA improved growth performance of dairy bulls by promoting nutrient utilization, microbial enzyme activity, microflora, and hepatic gene expression.