Effects of rumen-protected folic acid on ruminal fermentation, microbial enzyme activity, cellulolytic bacteria and urinary excretion of purine derivatives in growing beef steers

- Ruminal fermentation was modified by supplementary rumen-protected folic acid (RPFA).
- Microbial enzyme activities and ruminal degradability increased with supplementary RPFA.
- The growth of cellulolytic bacteria was promoted by supplementary RPFA.
- Urinary excretion of purine derivatives also increased with supplementary RPFA.

This experiment was done to investigate the influences of supplementary rumen-protected folic acid (RPFA) on ruminal fermentation parameters, microbial enzyme activity, cellulolytic bacteria and urinary excretion of purine derivatives in growing beef steers. Eight ruminally fistulated Jinnan beef steers (398.4 ± 1.9 kg) were used in a repeated 4 × 4 Latin square experimental design. The treatments were: control (without RPFA), low RPFA (LRPFA), medium RPFA (MRPFA) and high RPFA (HRPFA) with 0, 0.6, 1.2 and 1.8 g RPFA per steer per day, respectively. The dietary corn silage to concentrate ratio was 50:50 (dry matter [DM] basis). The dry matter intake was confined to 95% of voluntary intake. Mean ruminal pH was quadratically reduced with altering RPFA supplementation, and was the lowest for MRPFA and HRPFA, highest for the control, and intermediate for the LRPFA. Ruminal total VFA concentration was quadratically increased with increasing RPFA supplementation and was higher in MRPFA than in control. The ratio of acetate to propionate was quadratically increased due to the increased acetate concentration and the unchanged propionate concentration. Ruminal degradabilities of DM and neutral detergent fibre of corn silage, and DM and crude protein of concentrate mix increased quadratically with increasing RPFA supplementation. Ruminal enzyme activity of cellobiase, xylanase, pectinase and α-amylase quadratically increased and was higher in MRPFA than in control. The populations of B. fibrisolvens, R. albus, R. flavefaciens and F. succinogenes quadratically increased with altering the supplementary PRFA. Urinary excretion of purine derivatives quadratically increased with altering RPFA supplementation and was higher in HRPFA and MRPFA than in LRPFA and control. The results indicated that dietary supplements of RPFA improved ruminal fermentation, in situ ruminal degradation and urinary excretion of purine derivatives. It was suggested that the RPFA regulated the activity of rumen microbe or enzymes in a concentration-dependent manner. Under this experimental condition, the appropriate dose of RPFA was at 1.2 g/d for steer.