Energy value and use of glycerol for growing pigs

Glycerol is a by-product of biodiesel production from fat sources whose availability is increasing. The objectives of the present study were to determine the nutritive value and the conditions of its use for growing pigs. In a first trial, digestible (DE) and metabolizable (ME) energy of crude glycerol (99%) and glycerol urine content were assessed with increased levels of glycerol in the diet (3, 6, 9 and 12%). Urinary excretion of glycerol became high at 9 and 12% inclusion rate and represented 12 and 24% of glycerol intake respectively. Therefore, while glycerol digestive utilization was high (95%; DE = 16.8 MJ per kg) irrespective of diet level, ME (16.6 MJ per kg) decreased when the daily intake of glycerol exceeded 3 g per kg bodyweight and per day. Net energy (NE) value of crude glycerol was estimated in a second trial in respiratory chambers, with 7.5% glycerol in the diet corresponding to a low urinary excretion. Considering a 13.3 MJ NE/kg dry matter of crude glycerol, 4 levels of glycerin (82.5% glycerol) were compared in 30‐115 kg pigs. No significant effect of glycerin level was observed on growth performances and carcass characteristics, except a decrease (3%) of average daily gain between 30 and 70 kg bodyweight in pigs fed with 4 and 6% of glycerin in the diet.