The ileal digestibility of most amino acids is greater in red dog than in wheat middlings when fed to growing pigs.

The objective of this experiment was to determine the apparent ileal digestibility (AID) and the standardized ileal digestibility (SID) of CP and AA in 10 sources of wheat middlings and in 1 source of red dog. Ten diets that each contained 1 of the 10 sources of wheat middlings and 1 diet that contained red dog as the only source of protein and AA were formulated. An N-free diet was used to determine basal endogenous losses of CP and AA. Chromic oxide (0.4%) was added to all diets as an indigestible marker. Twelve pigs (BW: 29.23 ± 1.5 kg) were fitted with a T-cannula in the distal ileum. Pigs were allotted to a 12 × 8 Youden square design with 12 diets and eight 7-d periods. The initial 5 d of each period was the adaptation period, but ileal digesta were collected on the last 2 d of each period. Results indicated that the AID of CP in wheat middlings was 31.1 ± 6.9%, but the AID of CP in red dog (47.0%) was greater ( < 0.05) than the average AID of CP for wheat middlings. The AID of indispensable AA in wheat middlings ranged from 30.1 ± 5.4% for Lys to 67.7 ± 2.2% for His, and the AID of indispensable AA in red dog ranged from 53.7% in Val to 86.2% for Met. The average SID of CP in wheat middlings was 61.5 ± 5.1%, and there were no differences among the 10 sources of wheat middlings, but the SID of CP in red dog (78.5%) was greater ( < 0.05) than in wheat middlings. The SID of Arg, His, and Asp in wheat middlings was 81.4 ± 2.7%, 77.7 ± 2.1%, and 66.4 ± 2.7%, respectively, and no differences among sources of wheat middlings were observed for these AA. The SID of Met (73.6 ± 1.8%) and the SID of Ala (54.8 ± 4.9%) tended ( = 0.071 and = 0.090, respectively) to be different among sources of wheat middlings, and the SID of all other AA was different ( < 0.05) among the 10 sources of wheat middlings. There were no differences between red dog and wheat middlings for the SID of Arg, His, and Ser, and the SID of Cys was less ( < 0.05) in red dog than in wheat middlings, but for all other AA, the SID in red dog was greater ( < 0.05) than in wheat middlings. In conclusion, wheat middlings and red dog contain approximately the same quantities of AA, but the AID and SID of CP and most AA in red dog are greater than in wheat middlings.