The effect of glycerol inclusion on broiler performance and nutrient digestibility

1. Crude glycerol from biodiesel production was offered ad libitum to broiler chickens in a 21-d feeding and digestibility trial. The study was designed as a 3*2 + 1 factorial design with 3 concentrations (33, 67, 100 g/kg) of glycerol from 2 sources, A and B (PRS Environmental Ltd and John Thompson and Sons Ltd) and a control diet. The diets were formulated to contain apparent metabolisable energy (AME) of 12·95 MJ/kg (assuming 14·6 MJ/kg for glycerol). 2. No significant interactions occurred, so only the main effects were discussed. At 7-14 d, feed conversion ratio (FCR) showed a significant linear response with increased glycerol inclusion. However quadratic responses on FCR were observed for the 21-28 d period and 7-28 d. 3. Glycerol digestibility was significantly greater with birds offered the 67 g/kg and 100 g/kg glycerol-based diets in contrast to the digestibility of 33 g/kg glycerol-based diets. 4. Glycerol inclusion level also had an effect on AME, which increased linearly with increasing glycerol inclusion. Birds offered the diets containing glycerol also required less energy per unit gain in contrast to birds offered the control diet. 5. When examining the effect of source of glycerol, source A glycerol resulted in the highest AME (15·20 vs. 14·72 MJ/kg). There was no significant effect of glycerol source on the other performance parameters. 6. Glycerol digestibility was significantly greater with glycerol from source B (John Thompson and Sons, Ltd) with a mean value of 0·848 in contrast to source A (PRS Environmental), which had a somewhat lower mean glycerol digestibility of 0·757. 7. In conclusion, glycerol source did not affect performance and increasing level of glycerol improved FCR, with 67 g/kg inclusion resulting in the most efficient conversion of feed to gain without any negative effects upon nutrient digestibility.