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 per cent crude protein, 10 per cent fat, nine per cent acid detergent fibre (ADF) and 25 per cent (NDF). The concentrations of digestible energy (DE) and metabolizable energy (ME) in conventional sources of DDGS are approximately 3,500 and 3,350kcal per 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 six to nine per cent, 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 per cent 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 28.1kg. Each barrow was fed eightdifferent 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 per cent, with a mean of 29.94 per cent (Table 1). Fat content, expressed as acid hydrolysed ether extract, ranged from 5.25 to 10.58 per cent, with a mean of 7.92 per cent. The concentration of ADF ranged from 8.38 to 19.08 per cent, with a mean of 13.58 per cent, and NDF ranged from 23.42 to 33.26 per cent with a mean of 28.42 per cent.

Starch content ranged from not detectable to 6.60 per cent, with a mean of 1.33 per cent.

Gross energy (GE) ranged from 4,335 to 4,934kca per kg, with a mean of 4,556kcal per 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 548g per litre with a mean of 482g litre and particle size varied from 266 to 930μm with a mean of 589μm. These observations indicate that the sources of DDGS varied in the amount of solubles added to the distilled grains.

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
	DDGS
Item	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
Crude protein (%)	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
Hemicelluolose (%)	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/litre)	482	368	548	42.70	0.89
Particle size (µm)	589	266	930	177.58	0.30
1ND = not detectable

The concentration of DE in the 23 DDGS sources ranged from 3,145 to 3,786kcal per kg dry matter (DM), with a mean of 3,474kcal per kg DM (Table 2). The concentration of ME ranged from 2,880 to 3,598kcal per 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.

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
	DDGS
Item	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	93.60	<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

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.

Fibre 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.

The researchers add that they 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.

This report is based on unpublished research by S.M. Curry and H.H. Stein.

November 2014