Three experiments were conducted at the University of Murcia in Spain that determined the effects of dietary addition of crude glycerin on pellet production efficiency and the effects on growth performance and digestibility in growing-finishing pigs. Three dietary treatments were created by addition of 0, 2.5, or 5% crude glycerin to barley-soybean meal based diet, and 4 batches of each dietary treatment (2 each for grower and finisher diets) were prepared. In the manufacturing process, crude glycerin supplementation linearly increased the feeder speed and production rate (P < 0.05), resulting in a 20 to 29% improvement in the feed production rate compared with the control. Production efficiency (kg/kWh) increased linearly (P < 0.05) as the level of crude glycerin in feed increased.

A growth experiment with 240 barrows weighing about 30 kg showed that overall growth performance was not affected by dietary treatment, and there was no effect of dietary treatment on any plasma metabolite measured. A digestibility experiment involving nine pigs indicated that fecal digestibility of organic matter and ether extract were affected by dietary treatment, increasing linearly (P < 0.05) with increasing crude glycerin levels. However, neither CP digestibility nor N retention was affected by the glycerin content in either the growing or finishing period. Results of these experiments indicated that adding crude glycerin to the diet before pelleting improved feed mill production efficiency. The addition of crude glycerin up to 5% in the diet of growing-finishing pigs had no effect on growth performance, blood metabolites, nutrient digestibility, and N balance, but more studies are needed to determine how crude glycerin affects mineral metabolism and balance.