Distillers dried grains with solubles (DDGS) is a co-product of ethanol production that is often used in diets fed to pigs because of a relatively high concentration of amino acids (AA), energy, and digestible phosphorus. However, during the cooking and drying steps, the high temperature and concentration of moisture makes DDGS susceptible to the Maillard reactions, resulting in formation of sugar-amino acid complexes. Maillard reaction products result in reduced standardized ileal digestibility (SID) of amino acids (AA), with Lys being the most sensitive AA. However, there is limited information about how heating affects the concentration of digestible energy (DE) and metabolizable energy (ME). Therefore, the objective of these experiments were to test the hypothesis that both the degree of heating and the time that heat is applied will affect the concentration of DE and ME and the SID of AA in DDGS fed to growing pigs.

Materials and Methods

Nine sources of DDGS were used in the study. A conventional DDGS was either not autoclaved or autoclaved following one of 8 treatments: 110ºC for 15 or 30 min or 150ºC for 3, 6, 9, 12, 15, or 18 min. These 9 sources of DDGS were used in 2 experiments.

Experiment 1: Amino acid digestibility

Ten growing barrows with an average initial BW of 46.04 ± 3.90 kg had a T-cannula installed in the distal ileum. Pigs were allotted to a replicated 10 × 8 Youden square design with 10 diets and eight 7-day periods in each square. Pigs were placed in individual pens (1.2 by 1.5 m) that were equipped with a self-feeder, a nipple waterer, and a slatted tri-bar floor. The 10 diets included a N-free diet and one diet containing each of the 9 sources of DDGS as the sole source of AA. Ileal digesta were collected on d 6 and 7 of each 7-d period. At the conclusion of the experiment, all sources of DDGS, all diets, and all ileal digesta samples were analyzed for AA and values for the SID of AA in each source of DDGS were calculated.

Experiment 2: Energy digestibility and concentrations of DE and ME

A corn-diet and 9 diets based on corn and each of the 9 sources of DDGS were prepared. Thus, there were 10 diets in the experiment. Eighty growing barrows with an average initial BW of 33.74 ± 2.18 kg were allotted to a randomized complete block design with 10 diets and 8 replicate pigs per diet. There were 4 blocks with 20 pigs, and 2 pigs per diet in each block. Pigs were housed individually in metabolism crates that were equipped with a self-feeder, a nipple waterer, and a slatted floor. Urine and feces were collected for 5 d, and after determination of gross energy concentrations in diets, urine, and feces, concentrations of DE and ME in each source of DDGS were calculated.

Results

Experiment 1: Amino acid digestibility

The SID of CP, His, Leu, Met, Ala, Asp, Cys, Glu, and Gly was greater (P < 0.05) in the diet containing DDGS that was not autoclaved than in diets containing DDGS autoclaved at 110ºC (Table 1), but the SID of all AA was less (P < 0.01) if DDGS was autoclaved at 150ºC than at 110ºC. When samples were autoclaved at 110ºC, the SID of most AA decreased (linear, P < 0.05) with increasing duration of autoclaving, and there was reduced (linear, P < 0.01) SID of all AA if duration of autoclaving was increased at 150ºC.

Experiment 2: Energy digestibility and concentrations of DE and ME

The ATTD of GE, and the DE and ME (as-fed basis), and the DE and ME on a DM basis were greater (P < 0.01) in DDGS that had not been autoclaved than in DDGS that was autoclaved at 110ºC (Table 2), but the ATTD of GE and the metabolizability were less (P < 0.05) if DDGS was autoclaved at 150ºC than at 110°С. Additionally, there were linear decreases (P < 0.01) in ATTD of GE, in DE and ME (as-fed basis), and in DE and ME (DM basis) with increasing duration of autoclaving at 110ºC. However, there were no effects of time of autoclaving at 150°С on DE and ME.

Key points

• ATTD of GE, and DE and ME, are reduced if DDGS is autoclaved either at 110ºC or 150ºC.
• Digestibility of AA may be reduced if DDGS is autoclaved at 110ºC, and this reduction can be greater if DDGS is autoclaved at 150ºC and the longer the duration of autoclaving is the more the SID of AA are reduced.
• These results reflects the occurrence of Maillard reactions and the concentrations of reducing sugars as a result of heat damage.

Table 1. Standardized ileal digestibility (%) of CP and AA in distillers dried grains with solubles (DDGS) that was either not autoclaved or autoclaved at 110°C or 150°C ¹, Exp. 1

¹Data are least squares means of 8 observations per treatment.

²Values for standardized ileal digestibility were calculated by correcting apparent ileal digestibility values for basal endogenous losses. Basal endogenous losses were determine using pigs fed the N-free diet as (g/kg DMI): CP, 15.42; Arg, 0.51; His, 0.17; Ile, 0.27; Leu, 0.45; Lys, 0.34; Met, 0.07; Phe, 0.18; Thr, 0.58; Trp, 0.13; Val 0.40; Ala, 0.53; Asp, 0.73; Cys, 0.19; Glu, 0.86; Gly, 1.51; Pro, 4.11; and Ser, 0.58.

Table 2. Apparent total tract digestibility (ATTD) of GE, and concentration of DE and ME in corn and distillers dried grains with solubles (DDGS) that was either not autoclaved or autoclaved at 110°C or 150°C ¹, as-fed basis, Exp. 2

¹Data are least squares means of 8 observations per treatment.