Biodiesel is an alternative to petroleum-based diesel fuel and according to the National Biodiesel Board, there are currently 105 biodiesel production facilities operating in the United States, and 77 facilities are in the planning or construction stage. If all of these facilities are realized, the estimated US biodiesel production capacity will exceed 9.5 billion liters. This level of production would yield nearly 1.2 million metric tons of crude glycerol, the primary co-product of the biodiesel production process. Crude glycerol has the potential to be used as a feed ingredient in animal diets. However, little is known about glycerol’s nutritional value or how it impacts feed quality and feed production. Consequently, experiments sponsored by the National Pork Board, were carried-out to evaluate the effects of glycerol on feed characteristics, the pelleting process, and nursery pig growth performance.
The first experiment was designed to quantify the effects of added glycerol, soybean oil, or a 50:50 soy oil/glycerol blend on the flowability characteristics of ground corn or ground corn and 15 or 30% spray-dried whey. The experiment was conducted using corn ground by either a hammermill or a three-high roller mill. Feed flowability was determined by measuring the angle of repose four times for each sample. As was expected, roller mill ground grain had a lower angle of repose compared to grain ground with a hammermill, indicating less feed bridging would occur with roller mill ground grain. The addition of soy oil and spray-dried whey increased angle of repose, thus, decreasing flowability. Glycerol or a 50:50 soy oil/glycerol blend improved the flowability of the hammermill ground grain, but did not influence the flowability of the roller mill ground corn. Additionally, glycerol improved the flowability as spray-dried whey level increased. These data suggest that the addition of glycerol to a meal diet containing hammermill ground corn and spray-dried whey tends to improve flowability.
The second experiment was designed to evaluate how increasing levels of crude glycerol in diets effects pellet mill production efficiency. Diets were formulated to contain 0, 3, 6, 9, 12, and 15% crude glycerol. All diets were steam conditioned to 65.5°C and pelleted through a pellet mill equipped with a die that had an effective thickness of 31.8 mm and holes 3.96 mm in diameter. Increasing the level of crude glycerol in the diet up to 9% improved pellet quality. Additionally, glycerol tended to reduce the electrical energy consumption, thus improving pelleting efficiency. It was noted during the experiment that attempts to increase conditioning temperatures above 65.5°C resulted in slippage of the pellet mill rolls. Consequently, it appears that the inclusion of glycerol in a diet improves feed quality; however, glycerol inclusion levels may be limited due to a potential negative interaction with conditioning temperature. This observation needs to be investigated further.
A nursery pig growth performance trial was conducted to evaluate diets formulated with glycerol, soybean oil, or a blend of glycerol and soybean oil. A total of 182 pigs (initial BW, 11.0 ± 1.3 kg; 5 or 6 pigs/pen) were fed 1 of 7 corn-soybean meal-based diets with no added soy oil or crude glycerol (control), the control diet with 3 or 6% added soy oil, 3 or 6% added crude glycerol, and 6 or 12% addition of a 50:50 (wt/wt) soy oil/crude glycerol blend with 5 pens/diet. All diets were pelleted as described above, and pellet mill performance data was measured. The addition of crude glycerol lowered the temperature change across the pellet die, decreased pellet mill motor load, and improved production efficiency. The addition of crude glycerol also improved pellet durability compared with soybean oil and the soy oil/crude glycerol blend treatments. Pigs fed increasing levels crude glycerol had an increase in weight gain, but no differences were observed in the efficiency of gain. Both average daily gain and gain-to-feed tended to increase with increasing soy oil or the soy oil/crude glycerol blend. In summary, adding crude glycerol to the diet before pelleting increases pellet quality and improves feed mill production efficiency. The addition of 3 or 6% crude glycerol, soy oil, or a blend of soy oil and glycerol in nursery pig diets tended to increase weight gain. However, improved feed efficiency was only observed in the pigs fed soy oil or the soy oil/crude glycerol blend.
This study was designed to evaluate feasibility of replacing spray-dried whey with glycerol in nursery pig diets. A total of 350 weanling pigs 8-d after weaning (initial BW 6.3 ± 0.9 kg) were used in a 14-d growth assay. The pigs were fed one of ten diets that included 0, 3.6, or 7.2% lactose or 0, 3.6, or 7.2 % crude glycerol and fed in either meal or pelleted form. The changes in pellet temperature across the pellet die increased as lactose level increased, and decreased with the addition of glycerol. Pellet quality increased with the addition of both lactose and glycerol. Glycerol decreased the amount of energy required to pellet. Pigs fed the pelleted diets containing 7.2% glycerol had a decreased average daily gain to all of other treatments. Pigs fed the pelleted glycerol diets had a decreased average daily feed intake compared to pigs fed the pelleted lactose diets, and pigs fed diets containing either lactose of glycerol fed in meal form. Thus, based on these results, adding glycerol to diets prior to pelleting tends to improve pellet quality and decreases energy cost. However, it does not appear glycerol can replace lactose in weanling pig diets.
