Oven drying of ileal digesta from growing pigs reduces the concentration of AA compared with freeze drying and results in reduced calculated values for endogenous losses and elevated estimates for ileal digestibility of AA

Two experiments were conducted to evaluate the influence of drying method on the composition of ileal digesta and the standardized ileal digestibility (SID) of CP and AA in feed ingredients fed to pigs. The hypothesis was that oven drying of ileal digesta samples results in loss of N and AA, and therefore, in greater calculated values for SID of CP and AA compared with lyophilized samples. In Exp. 1, eight barrows (13.8 ± 0.5 kg BW) were equipped with a T-cannula in the distal ileum and randomly allotted to a replicated 4 × 4 Latin square design with four diets and four periods, for a total of eight replicate pigs per diet. Three diets containing three different sources of soybean meal as the sole source of AA and an N-free diet were used. In Exp. 2, 18 cannulated growing barrows (72.5 ± 9.2 kg BW) were allotted to a completely randomized design with three diets and six replicate pigs per diet. The three diets included two diets based on two sources of distillers dried grains with solubles and an N-free diet. In both experiments, ileal digesta samples were collected for 8 h on days 6 and 7 of the 7-d feeding period. At the conclusion, two representative sub-samples were collected from each ileal digesta sample. One sub-sample was lyophilized and the other was oven dried at 60 °C using a forced air oven. Results indicated that in both experiments, DM was greater (P < 0.05) in lyophilized samples than in oven dried samples. There was no difference in the SID of CP between the two drying methods. However, except for Ala and Val in Exp. 1, the concentration of AA (88% DM-basis) was greater (P < 0.05) in lyophilized samples than in oven dried samples, which resulted in reduced calculated values for basal endogenous losses of AA. Therefore, values for the SID of AA (except for Ala in Exp. 1 and Trp and Gly in Exp. 2) were greater (P < 0.05) when calculated from oven dried samples than from lyophilized samples. In conclusion, regardless of the diet, oven drying of ileal digesta samples does not result in loss of N, but appears to damage or convert AA to other N-containing compounds, which results in reduced estimates for basal endogenous losses and greater calculated values for SID of AA. Thus, freeze drying of ileal digesta samples is recommended when data for the SID of AA are calculated for feed ingredients fed to pigs.