Energy digestibility in 23 sources of distillers dried grains with solubles fed to pigs

Distillers dried grains with solubles (DDGS) is a co-product of the ethanol industry and is often used as an economical source of energy and protein in swine diets. Conventional DDGS contains approximately 27% crude protein, 10% fat, 9% acid detergent fiber (ADF), and 25% (NDF). The concentrations of digestible energy (DE) and metabolizable energy (ME) in conventional sources of DDGS are approximately 3,500 and 3,350 kcal/kg, respectively. However, there is significant variation in the way different plants produce DDGS. For example, in recent years ethanol plants have begun extracting oil from DDGS to sell to the biodiesel industry. This results in DDGS with its fat content reduced to approximately 6 to 9%, which may result in lower concentrations of DE and ME.

If pigs are fed diets containing decreased levels of DE and ME relative to conventional DDGS, a reduction in growth performance may result. This would make DDGS a less economical feedstuff. An experiment was conducted to determine the variability of DE and ME in DDGS produced in and around Illinois.

Experimental design

A total of 23 sources of DDGS were used in the experiment. DDGS samples were procured from ethanol plants throughout the Midwestern United States: eleven from Illinois, four from Indiana, four from Iowa, two from Missouri, and two from Wisconsin. A basal diet of corn, minerals, and vitamins was formulated. Each of the experimental diets contained 40% of one of the 23 sources of DDGS, added to the basal diet at the expense of corn. These diets were then fed to 24 growing barrows with an average initial body weight of 28.1 kg. Each barrow was fed 8 different sources of DDGS in such a way that no barrow received the same source of DDGS more than once.

Results

The crude protein content of DDGS ranged from 24.58 to 32.21%, with a mean of 29.94% (Table 1). Fat content, expressed as acid hydrolyzed ether extract, ranged from 5.25 to 10.58%, with a mean of 7.92%. The concentration of ADF ranged from 8.38 to 19.08%, with a mean of 13.58%, and NDF ranged from 23.42 to 33.26% with a mean of 28.42%. Starch content ranged from not detectable to 6.60%, with a mean of 1.33%. Gross energy (GE) ranged from 4,335 to 4,934 kcal/kg, with a mean of 4,556 kcal/kg. The reduced mean concentration of fat in these sources of DDGS compared with conventional DDGS indicates that most of these sources had had oil extracted, in varying amounts. With some of the fat removed, there were proportionately greater concentrations of other nutrients. The efficiency of starch fermentation also differed significantly among ethanol plants.

Bulk density varied from 368 to 548 g/L with a mean of 482 g/L, and particle size varied from 266 to 930 μm with a mean of 589 μm. These observations indicate that the sources of DDGS varied in the amount of solubles added to the distilled grains.

The concentration of DE in the 23 DDGS sources ranged from 3,145 to 3,786 kcal/kg DM, with a mean of 3,474 kcal/kg DM (Table 2). The concentration of ME ranged from 2,880 to 3,598 kcal/kg DM, with a mean of 3,173 kcal/kg DM. The mean values are less than the values for conventional DDGS observed in previous studies.

Using concentrations of ash, GE, NDF, and lignin, as well as bulk density and particle size, we were able to generate moderately accurate prediction equations for DE and ME in DDGS. Although fat content was different among the sources of DDGS, it was not a component of the equations.

DE = –688.58 – 6.11*ash + 0.69*GE + 3.06*NDF – 7.89*lignin + 1.44*bulk density – 0.26*particle size (r2 = 0.78)

ME = –784.30 – 7.88*ash + 0.67*GE + 5.48*NDF – 6.80*lignin + 2.22*starch – 0.48*particle size (r2 = 0.74)

Key points

  • The concentrations of DE and ME in DDGS varies significantly due to differences in processing techniques. The mean values for DE and ME were less than the values for conventional DDGS reported from previous studies.
  • Fiber content and the amount of solubles added to DDGS accounted for most of the variability of DE and ME among DDGS sources in this study.
  • We were able to generate moderately accurate prediction equations for DE and ME in DDGS, but more research will be needed to generate equations with higher accuracy.

Table 1. Proximate analysis, gross energy, carbohydrate concentration, bulk density, and particle size of 23 sources of distillers dried grains with solubles (DDGS), as-fed basis

Item

DDGS

 

Mean

Low

High

SD

CV

DM, %

90.36

87.93

93.29

1.09

1.20

Ash, %

5.98

4.86

7.42

0.76

12.79

CP, %

29.94

24.58

32.21

1.76

5.89

AEE, %

7.92

5.25

10.58

1.29

0.16

GE, kcal/kg

4,556

4,335

4,934

135.21

2.97

ADF, %

13.58

8.38

19.08

2.45

18.01

NDF, %

28.42

23.42

33.26

2.87

10.09

Lignin, %

3.92

0.96

7.15

1.36

34.74

Hemicellulose, %

14.84

10.19

19.18

2.29

15.43

Cellulose, %

9.66

6.22

11.93

1.38

14.28

Starch, %

1.33

ND1

6.60

1.68

126.56

Bulk density, g/L

482

368

548

42.70

0.89

Particle size, μm

589

266

930

177.58

0.30

1ND = not detectable.

 

Table 2. Concentration of DE and ME, daily N balance, and apparently total tract digestibility (ATTD) of GE and N in distillers dried grains with solubles (DDGS), as-fed basis

Item

DDGS

 

Mean

Low

High

SEM

P-value

DE, kcal/kg

3,139

2,822

3,437

73.88

<0.01

DE, kcal/kg DM

3,474

3,145

3,786

81.57

<0.01

ME, kcal/kg

2,867

2,584

3,230

93.6

<0.01

ME, kcal/kg DM

3,173

2,880

3,598

103.53

<0.01

ATTD of GE, %

70.0

62.7

89.3

1.6

<0.01

 

This report is based on unpublished research by S. M. Curry and H. H. Stein.

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