Nutrient Digestibility of Heat- or Heat Plus Citric Acid-Pretreated DDGS for Pigs

A study was conducted to determine effects of pretreating whole stillage (WS) with heat or heat plus diluted citric acid (heat+CA) on nutrient digestibility of the resulting DDGS for growing pigs. The WS was untreated or pretreated with heat (160^oC at 70 psi for 20 min) alone (heat) or with the heat plus CA (12 g/L; heat+CA). Untreated and pretreated WS were paddle-dried before their inclusion in diets. Five diets were fed; they included cornstarch-based containing DDGS, untreated WS, heat-pretreated WS, or heat+CA-pretreated WS as the sole source of protein; and N-free diet, which was included for estimation of basal endogenous losses of AA. The DDGS diet was included for comparison. The 5 diets were fed to 10 ileal-cannulated barrows (57 ± 1.53 kg BW) in a replicated 5 × 5 Latin square to give 10 replicates/diet. On DM basis, DDGS contained 30.7% CP, 3.7% starch, 3.6% ether extract (EE), and 34.2% NDF; whereas untreated WS contained 37% CP, 4.5% starch, 9.5% EE, and 36.5% NDF. Comparing to the untreated WS, pretreatment of WS with heat or heat+CA improved (P < 0.001) apparent ileal digestibility (AID) of GE in diet from 74.2 to 82.3 or to 79.7%, respectively; AID of CP in diet from 78.2 to 84.7 or to 82.0%, respectively; and AID of EE in diet from 84.4 to 89.2 or 90.4%, respectively. Pretreatment of WS with heat or heat+CA did not affect apparent total tract digestibility (ATTD) of GE in diet. The untreated WS diet had lower (P < 0.001) AID and ATTD of GE than DDGS diet by 4 and 2%, respectively. However, untreated WS diet had greater (P < 0.001) AID of EE than DDGS diet by 4%. Pretreatment of WS with heat reduced (P < 0.001) standardized ileal digestibility (SID) of Met, Thr, and Trp by 9.7, 11.2, and 3.6%, respectively, but did not affect SID of Lys. Pretreatment of WS with heat+CA reduced (P < 0.001) SID of Met, Thr, and Trp by 11.4, 14.6, and 32%, respectively; and tended to reduce (P = 0.062) SID of Lys by 12.6%. Untreated WS and DDGS did not differ in SID of AA. In conclusion, pretreatment of WS with heat or heat+CA improved energy digestibility, but reduced AA digestibility. Thus, pretreatment and drying of WS at conditions employed in the current study can improve energy value, but reduce AA availability of the resulting DDGS for pigs.