Effect of feed conditioning time prior to pelleting on standardized ileal digestibility of amino acids and total tract digestibility of energy in diets fed to growing pigs.

Two experiments were conducted to determine the effect of increasing retention time in the conditioner prior to pelleting on digestibility of energy, protein, and amino acids (AA) in diets for growing pigs. Four dietary treatments were used in both experiments and consisted of a mash diet, and 3 pelleted diets that were conditioned for 30, 60, or 180 s. In Exp. 1, 12 ileal canulated barrows with an initial average body weight of 44.9 ± 2.70 kg were allotted to a triplicated 4 × 4 Latin square with 4 dietary treatments and 4 experimental periods in each square for a total of 12 replicate pigs per treatment. Each period consisted of 5 days of adaptation and 2 days of collection of ileal digesta. In Exp. 2, 12 barrows (initial average body weight: 34.1 ± 1.03 kg) were allotted to a triplicated 4 × 3 incomplete Latin square design with 4 dietary treatments and 3 experimental periods. Each period consisted of 5 d of adaptation and 5 d of collection of feces and urine. Pigs were individually housed in metabolism crates and feces, and urine were collected. Results of Exp. 1 indicated an overall treatment effect (P < 0.05) on standardized ileal digestibility (SID) of crude protein and all AA except Lys, Met, and Trp. The SID of crude protein, Arg, Leu, Thr, Ala, Ser, and Tyr was greater (P < 0.05) in all pelleted diets compared with the mash diet. The SID of His, Ile, Phe, Val, Asp, and Glu was less (P < 0.05) in the mash diet compared with the pelleted diets conditioned for 60 s or 180 s. The SID of Cys was less (P < 0.05) in the mash diet compared with the pelleted diet conditioned for 180 s. Increasing the retention time in the conditioner from 30 to 180 s increased (linear; P < 0.05) the SID of CP and most AA. Results of Exp. 2 demonstrated that pelleted diets had greater (P < 0.05) apparent total tract digestibility (ATTD) of gross energy compared with the mash diet, but no treatment effects were observed for ATTD of dry matter or on digestible energy, metabolizable energy or the metabolizability of digestible energy. These results indicate that increasing conditioning time up to 180 s improved AA digestibility for most AA and pelleting also increased ATTD of gross energy.