Comparative ileal digestibility of gross energy and amino acids in low and high tannin sorghum fed to growing pigs

Low tannin sorghum cultivars (LTS) have been previously proved to contain greater available energy and apparent total tract digestibility (ATTD) of gross energy (GE) and crude protein (CP) than high tannin sorghum cultivars (HTS); however, their comparative ileal digestibility of energy and nitrogen excluding microbial interference in pigs remains mostly unknown. This study was designed to compare apparent (AID) and standardized ileal digestibility (SID) of amino acids (AA) associated with the AID and hindgut disappearance (HGD) of GE and CP in 4 LTS and 4 HTS fed to growing pigs. Eighteen barrows (27.6 +/- 3.5 kg) fitted with a distal ileum T-cannula were allotted to a replicated 9 x 3 Youden square design with 9 diets and 3 periods to give a total of 6 replicate pigs per diet. Each period lasted 10 days, with 5 days adaption to the diets followed by 3 days collection of faeces and then 2 days collection of ileal digesta. Eight sorghum diets contained 966 g/kg sorghum grain as the only source of dietary energy and nitrogen, and one nitrogen-free diet was used to determine basal ileal endogenous nitrogen loss. Mean AID, ATTD, and HGD of GE and CP were higher in LTS than in HTS (P < 0.05). Mean SID of 8 out of 15 AA were decreased in HTS (P < 0.05). The AID, ATTD, and HGD of GE or CP had a negative correlation with condensed tannins and total phenolics in sorghum grain (P < 0.05). The SID of essential AA, including lysine, threonine, valine, histidine, and arginine, were highly or moderately negatively correlated with condensed tannins and total phenolics content in sorghum grains (P < 0.05). Overall, HTS provided less ileal digestibility and hindgut disappearance of energy and nitrogen, implying that condensed tannins in sorghum grain may impede nutrient digestibility, not only in the foregut but also in the hindgut segements of pigs.