Relationship between digestibility index marker and dietary characteristics in the determination of energy and nutrient utilization for pigs and broiler chickens

The objective of this study was to investigate the effect of type and level of digestibility index marker (DIM) and dietary characteristics including dietary fiber type, dietary protein sources, and inclusion of xylanase in pigs and broiler chickens.

An experiment was conducted to investigate if (i) the apparent digestibility of gross energy (GE) and nitrogen (N) were influenced by the type of DIM and dietary fiber; (ii) the concentration pattern of DIM was influenced by dietary fiber, ileal digesta collection day (Day), and time period (TP). Eighteen barrows (initial BW = 24.2 ± 0.3 kg) fitted with a T-cannula at the end of the ileum were used in a 2-period study. Three corn-soybean meal-based diets were formulated with corn starch, corn bran or oat bran at 100 g/kg. Acid insoluble ash (AIA), chromic oxide (Cr₂O₃), and titanium dioxide (TiO₂) were included as DIM in each diet. Each period consisted of a 7-d adjustment period followed by a 3-d total fecal collection period and a 3-d ileal digesta collection period, where ileal digesta was collected every 3 h between 09:00 to 21:00 h with 4 TP on each of the 3 day. The DIM had similar effect on apparent ileal digestibility (AID) of GE and N within each diet, but different effects among the 3 diets. However, the apparent total tract digestibility (ATTD) of GE or N of corn starch and the ATTD of N of corn bran determined by the 3 DIM were not different. The recovery of TiO₂in feces of pigs fed the oat bran was 78.3%, which was the least among the 3 diets (P< 0.05). The distribution of Cr concentration in ileal digesta of pigs fed cornstarch, corn bran, and oat bran was similar to that of Tiand AIA irrespective of TP. In conclusion, the AID of GE or N was more influenced by the choice of DIM compared with ATTD; the recovery of TiO₂in pigs fed oat bran was less than corn starch or corn bran; the Day had limited effect on DIM concentration; and the three DIM moved synchronously in diets irrespective of TP.

Another study was conducted to investigate if the AID of GE or N was influenced by inclusion level and type of DIM and inclusion level of OB, and if the ATTD of GE or DIM recovery was influenced by the three aforementioned factors and duration of feces collection. Six diets were formulated as a 2 ´3 factorial arrangement with two levels of OB (0 or 100 g/kg) and three levels of DIM (2.5, 5.0, or 7.5 g/kg). BothCr₂O₃and TiO₂were added to the same diet as DIM and their inclusion levels were consistent in each experimental diet.In Exp. 1, eighteen barrows (initial BW = 24.2 ± 0.3 kg) fitted with T-cannulas at the distal ileum were used in a triplicate 6 × 2 incomplete Latin Square design with 6 dietary treatments and 2 periods. The ileal digesta were collected for 3 d after 5-d adaptation. In Exp. 2, a total of 72 barrows (initial BW = 26.9 ± 0.5 kg) were used in a randomized complete block design, and the feces were collected for either 3 or 5 d after a 7-d adaptation according to the assignment. Experimental diets were same as Exp. 1. The AID of GE and N determined by TiO₂were greater (P< 0.05) than Cr₂O₃regardless of the OB level and DIM level. Neither the OB level nor the DIM level affected the AID of GE or N. The DIM level and duration of feces collection had no effect on ATTD of GE and DIM recovery. The ATTD of GE were greater (P< 0.05) determined by TiO₂than that determined by Cr₂O₃. Similarly, the recovery of TiO₂was greater (P= 0.007) than Cr₂O₃. Inclusion of 100 g/kg OB did not affect the recovery of DIM. In conclusion, the AID of GE and N, the ATTD of GE, and the recovery of Cr₂O₃or TiO₂were affected by DIM type, but not DIM level; the inclusion of OB had no effect on AID of GE and N, and DIM recovery; and the duration of feces collection had no effect on ATTD of GE, and DIM recovery.

The additivity of AID and standardized ileal digestibility (SID) of crude protein (CP) and amino acids (AA) in mixed diets containing wheat, canola meal (CM), meat and bone meal (MBM), and sorghum distillers’ dried grains with solubles (DDGS) fed to pigs with Cr₂O₃and TiO₂as DIM was investigated in the third study. Four diets were prepared to contain wheat, CM, MBM, or DDGS as a sole source of N; three mixed diets were prepared to contain wheat, CM, and MBM; wheat, MBM, and DDGS; or wheat, CM, MBM, and DDGS; and a N-free diet was prepared to estimate the BEL of CP and AA. Both Cr₂O₃and TiO₂, each at 5 g/kg were incorporated into each diet. Sixteen barrows (initial BW = 34.7 ± 0.6 kg) surgically fitted with T-cannulas at the distal ileum were allotted to a duplicate 8 × 4 incomplete Latin square design with 8 experimental diets and 4 periods. Chromic oxide and TiO₂determined similar BEL, AID, and SID of CP and AA. In wheat-CM-MBM diet, the measured AID of CP and most AA determined with Cr₂O₃or TiO₂were not different from the predicted values. The results indicated that the determination of BEL, AID, and SID of CP and AA were not affected by DIM type;the additivity of AID and SID of CP and most indispensable AA in mixed diets was not affected by DIM type; and more accurate prediction of ileal digestibility of AA was achieved using SID rather than AID in mixed diets containing wheat, CM, MBM, and DDGS.

The aim of the last study was to investigate the growth performance and nutrient utilization responses of broiler chickens and the nutrient utilization of pigs to xylanase, experimental diet formulation method for energy (FME), and DIM. In Exp. 1, a total of 448 male broiler chickens were used in a randomized complete block design with BW as a blocking factor. Seven dietary treatments were prepared in a 3 × 2 + 1 factorial arrangement with inclusion of sand, diatomaceous earth (DAE), or wheat bran (WB) as FME and without or with xylanase (26,400 unit/kg of diet) plus positive control, which contained sufficient energy content for animals. Each of Cr₂O₃and TiO₂were incorporated at 5 g/kg in diets. In Exp. 2, twenty-one barrows (initial BW = 33.0 ± 0.3 kg), fitted with simple T-cannulas at the distal ileum, were used in a triplicate 7 × 2 incomplete Latin Square design with 7 dietary treatments, which were prepared by the same arrangement as in broilers. In Exp. 1, the growth performance of birds was not affected by xylanase, but was affected by the choice of FME. There were interactions (P< 0.05) between xylanase and FME for AID of CP, His, Met, Thr, and Trp. In Exp. 2, there were interactions (P< 0.05) between xylanase and FME for AID of dry matter, GE, Arg, and Lys. The DIM type had no effect on responses in pigs. In conclusion, the efficacy of xylanase on ileal energy and AA digestibility depends on the choice of FME in broilers and pigs, and DIM affects ileal digestibility in broilers.

In summary, the AID of GE or N was more influenced by the DIM type compared with ATTD, and the three DIM moved synchronously in diets irrespective of TP. The AID of GE and N, the ATTD of GE, and the recovery of Cr₂O₃or TiO₂were affected by DIM type, but not DIM level. However, the choice of DIM had no effect on the determination of BEL, AID, and SID of CP and AA, and additivity of AID and SID of CP and most indispensable AA in mixed diets. In addition, more accurate prediction of ileal digestibility of AA was achieved using SID rather than AID in mixed diets containing wheat, CM, MBM, and DDGS. Finally, the efficacy of xylanase on ileal energy and AA digestibility depends on the choice of FME in broilers and pigs, and DIM affects ileal digestibility in broilers.