A Kansas State University (KSU) research team recently investigated whether glycerol, a byproduct of the biofuels industry, could decrease diet cost by replacing corn as an energy source. They also looked at whether adding glycerol to a corn-soybean meal diet prior to pelleting could help reduce wear and tear on pelleting machines.

Crude glycerol is the primary co-product of the biodiesel production process. If U.S. biodiesel production facilities continue to multiply as predicted, biodiesel production capacity will soon exceed 2.5 billion gal. This level of production will yield nearly 1.3 million tons of glycerol.

Part of the glycerol is currently processed into an industrial chemical. However, the industrial glycerol market is already saturated. Interest has been growing in utilizing crude glycerol as a livestock feed ingredient to reduce diet costs. But little has been known about glycerol's nutritional value, or how it might impact feed quality and feed processing efficiency.

A series of KSU experiments looked at the effect glycerol might have on pellet mill production efficiency.

Three experimental diets were manufactured and pelleted, and data was collected at the KSU Grain Science Feedmill. All of the diets were steam- conditioned and pelleted at specific temperatures, using a pellet mill equipped with a 4 × 32 mm pellet die.

The six treatments in the first experiment were made up of a corn-soybean meal-based swine grower diet, formulated to contain 0, 3, 6, 9, 12 and 15% crude glycerol.

Experiment two included seven treatments: a control diet with no added soy oil or glycerol; the control diet with 3% or 6% added soy oil; the control diet with 3% or 6% added glycerol; or the control diet with 6% or 12% of a 50:50 soy oil-to-glycerol blend. Experiment three included five treatments: a control with no added lactose or glycerol; the control diet with 3.6 or 7.2% lactose; or 3.6 or 7.2% glycerol.

Each experimental diet was replicated by manufacturing a new batch of feed three times. Pellet mill electrical consumption, production rate, hot pellet temperature, motor load, feeder rate, conditioning rate and pellet durability were measured.

The researchers concluded the glycerol improved pellet quality in all three experiments. The addition of glycerol should increase the production efficiency of the pelleting process and decrease energy cost for the pellet mill. The data indicate glycerol can be added to a diet with soy oil in a blend to improve pellet production efficiency and pellet quality, compared to a diet containing only soy oil. Specific information about how each dietary formulation performed during the pelleting process is contained in Tables 1, 2 and 3.

Using the diets from the second experiment, the researchers also evaluated the effects of glycerol, soy oil and a 50:50 soy oil/glycerol blend on nursery pig performance.

The seven dietary treatments were corn-soybean meal-based control diet with no added soy oil or glycerol; the control diet with 3% or 6% added soy oil; 3% or 6% added glycerol; and 6% or 12% additions of a 50:50 soy oil/glycerol blend.

The diets were fed to 182 pigs in a 26-day growth period. Pigs weighed around 23 lb. at the beginning of the trial, and were randomly allotted to treatment, with between five and six pigs/pen, and five pens/treatment.

The results indicated glycerol can be included in a diet up to 6%, either alone or in combination with soy oil without affecting final body weight in pelleted phase 2 nursery diets. Pigs fed increasing levels of glycerol had increased average daily feed intake (ADFI). Feed:gain increased with increasing soy oil or the soy oil/glycerol blend, resulting in similar average daily gain between pigs fed soy oil, glycerol or the 50:50 soy oil/glycerol blend.

Adding glycerol to the diet did not influence feed:gain compared to the control. Results of the feeding trials are shown in Table 4.

Glycerol could be added in place of corn in some swine diets to decrease diet cost, according to the researchers. Glycerol's benefits during the pelleting process can also help lead to energy savings for the production mill.

Researchers: Crystal N. Groesbeck; Leland. J. McKinney; Joel M. DeRouchey; Mike D. Tokach; Robert D. Goodband; Jim L. Nelssen; Steve S. Dritz, DVM; Allen W. Duttlinger; and Keith C. Behnke, Kansas State University. Contact Groesbeck at 785-532-1270 or email cgroesbe@ksu.edu.

Table 1. Effects of Added Glycerol on Pellet Production Efficiency, Exp. 1ab
Added Glycerol, %
Item 0 3 6 9 12 15
Conditioning temperature, °F 149.7 150.0 150.2 150.2 149.8 149.8
Hot pellet temperature, °F 169.1 167.8 166.1 169.9 161.9 163.0
Delta temperature, °F 18.9 17.3 15.5 19.2 11.7 12.6
Voltage, volts 250.4 250.0 248.9 252.3 250.1 250.3
Amperage, amps 29.3 25.2 23.6 22.9 19.5 18.1
Motor load, % 54.7 45.7 41.7 41.0 33.3 30.3
Pellet durability index
Standard, % 90.1 92.1 93.5 95.7 94.9 94.7
Modified, % 87.5 89.4 91.2 93.9 92.3 91.6
Production rate, tons/hour 1.32 1.27 1.24 1.11 1.09 1.10
Total energy, kilowatt hour/ton 7.62 6.81 6.51 7.09 6.10 5.60
aAll diets were corn-soybean meal-based swine grower diets.
bEach experimental diet was replicated by manufacturing a new batch of feed three times.
Table 2. Effects of Added Glycerol on Pellet Production Efficiency, Exp. 2ab
Soy Oil Glycerol Blendc
Item Control 3% 6% 3% 6% 6% 12%
Conditioning temp., °F 150.4 151.3 150.6 151.3 150.5 151.1 150.4
Hot pellet temp., °F 171.1 165.5 161.0 165.4 164.1 159.9 156.7
Delta temp., °F 20.2 13.9 10.0 13.7 13.2 8.4 5.9
Voltage, volts 247.7 249.9 245.8 248.4 250.1 249.4 249.3
Amperage, amps 28.3 23.0 19.6 23.7 22.8 20.9 16.0
Motor load, % 53.6 45.9 34.6 42.9 41.6 36.3 26.9
Pellet durability index
Standard, % 92.6 81.6 58.3 94.7 95.5 85.4 80.3
Modified, % 89.9 74.7 40.0 91.9 92.2 78.3 65.8
Production rate, tons/hour 1.38 1.42 1.40 1.35 1.38 1.40 1.36
Total energy, kilowatt hour/ton 7.58 6.09 5.16 6.50 6.18 5.45 4.44
aAll diets were formulated to the same lysine to metabolizable energy ratio.
bEach experimental diet was replicated by manufacturing a new batch of feed three times; each run consisted of 750-lb. batches.
cAddition of 50% soy oil and 50% glycerol.
Table 3. Effects of Added Glycerol on Pellet Production Efficiency, Exp. 3a
Lactose Glycerol
Item Control 3.6% 7.2% 3.6% 7.2%
Conditioning temperature, °F 150.3 150.2 150.3 149.7 150.3
Hot pellet temperature, °F 166.9 168.3 171.3 164.5 158.3
Delta temperature, °F 16.5 18.2 20.9 14.7 8.0
Voltage, volts 252.2 251.9 248.0 251.7 252.3
Amperage, amps 21.6 22.2 23.0 19.3 17.2
Motor Load, % 33.8 37.1 38.4 30.1 27.1
Pellet durability index
Standard, % 86.1 88.5 90.1 89.9 91.8
Modified, % 87.0 89.2 90.8 89.8 92.0
Production rate, tons/hour 0.98 1.03 1.02 0.99 0.97
Total energy, kilowatt hour/ton 8.10 8.00 8.20 7.20 6.60
aEach experimental diet was replicated by manufacturing a new batch of feed three times;
each run consisted of 750-lb. batches.
Table 4. Effects of Glycerol on Pellet Mill Production and Nursery Pig Performance
Soy oil, % Glycerol, % Blend, %
Item Control 3 6 3 6 6 12
Pellet mill data
Amperage, amps 28.2 23.0 19.6 23.7 22.8 20.9 16.0
Motor load, % 53.6 45.9 34.6 42.9 41.6 36.2 26.9
Production efficiency, kilowatt hour/ton 7.8 6.1 5.2 6.5 6.2 5.5 4.3
Pellet durability index, % 93.0 81.6 58.3 94.7 95.5 85.4 80.3
Day 0 to 26
Average daily gain, lb. 1.17 1.26 1.22 1.25 1.26 1.22 1.25
Average daily feed intake, lb. 1.73 1.73 1.68 1.79 1.80 1.67 1.68
Feed/gain 0.68 0.73 0.73 0.70 0.70 0.73 0.74
Final weight, lb. 54.34 56.76 55.88 56.76 56.76 55.88 56.54