Effects of feed intake and dietary nutrient density on apparent ileal and total tract digestibility of nutrients and gross energy for growing pigs

The present study was conducted to investigate the effects of feed intake (FI) and dietary nutrient concentration on the determination of apparent ileal digestibility (AID) and apparent total tract digestibility (ATTD) of nutrients and GE for growing pigs. A total of 48 growing pigs (40.7 +/- 1.3 kg initial BW) were surgically fitted with simple T-cannulas at the distal ileum and assigned to 6 treatment groups in a 2 x 3 factorial arrangement of 2 diets (a low-nutrient-density [LND] diet or a normal-nutrient-density [NND] diet) and 3 FI levels (3, 4 or 5% of BW per day). The experimental period consisted of a 5-d adjustment period: 2 d of feces collection (on d 6 and 7), and 2 d of ileal digesta collection on (d 8 and 9). Chromic oxide was used as an indigestible marker to calculate AID of AA and AID and ATTD of CP, ether extract (EE), ash, ADF, NDF, total carbohydrates (CHO), and GE. The AID of CP (P < 0.05), EE (P < 0.1), ash (P < 0.05), and GE (P < 0.1); the ATTD of ash (P < 0.1); and the hindgut disappearance of CP (P < 0.05), ash (P < 0.1), and most AA were affected by the interaction of dietary nutrient density and FI level. The AID of CP and the AID and ATTD of DM, EE, CHO, and GE linearly decreased for pigs fed a NND diet as FI increased (P < 0.05). Furthermore, the AID of CHO (P < 0.1) and NDF (P < 0.05), the ATTD of DM (P < 0.1), and the hindgut disappearance of CHO and NDF (P < 0.1) were influenced by FI. When pigs were fed the NND diet, the AID of most AA decreased (linear, P < 0.05) with increasing FI. However, there were no linear or quadratic effects of FI levels on the AID, ATTD, and the hindgut disappearance of DM, CP, EE, CHO, NDF, ADF, and GE and the AID of most AA for pigs fed the LND diet. In summary, the AID and ATTD of nutrients and GE response of growing pigs to FI levels are dependent on dietary nutrients density. The AID and ATTD of nutrients and GE decreased for pigs fed the NND diet as FI increased.