Effects of glycerol on rumen fermentation, urinary excretion of purine derivatives and feed digestibility in steers

The objective of this study was to evaluate the effects of glycerol supplementation on rumen fermentation, urinary excretion of purine derivatives and feed digestibility in the total tract of steers. Eight ruminally cannulated Simmental steers (450 ± 12 kg) were used in a replicated 4 × 4 Latin Square arrangement of treatments with experimental period of 21 days long. The treatments were: control (without glycerol), LG, MG and HG with 100, 200 and 300 g glycerol per head per day, respectively. Diet consisted of 60% corn stover and 40% concentrate (dry matter [DM] basis). Dry matter intake (averaged 9 kg/day) was restricted to a maximum of 90% of ad libitum intake. Ruminal pH (range of 6.58 to 6.23) was linearly (P < 0.05) decreased, whereas total VFA concentration (range of 93.40 to 99.61 mM) was linearly (P < 0.03) increased with increasing glycerol supplementation. Ratio of acetate to propionate decreased linearly (P < 0.02) from 4.56 to 3.64 as glycerol supplementation increased due to the increased in propionate production. In situ ruminal NDF degradation of corn stover was improved but the CP degradability of concentrate mix was decreased with increasing doses of glycerol. Urinary excretion of purine derivatives was quadratically (P < 0.02) changed with altering glycerol supplementation (65.0, 65.7, 71.1 and 67.2 mmol/d for control, LG, MG and HG, respectively). Similarly, digestibilities of OM, NDF and CP in the total tract were also linearly increased with increasing glycerol. The results indicate that glycerol supplementation potentially improves rumen fermentation with increased propionate production and feed digestibility in the total digestive tract of beef cattle. It suggests that feeding glycerol stimulates the ruminal microorganisms or digestive enzymes in a dose-dependent manner. Under the current experimental conditions, the optimum glycerol dose was about 200 g glycerol per head per day.