Effects of supplemental phytic acid on the apparent digestibility and utilization of dietary amino acids and minerals in juvenile grass carp (Ctenopharyngodon idellus)

A feeding trial was conducted for 8weeks to evaluate the effects of supplemental phytic acid (PA) on the apparent digestibility and utilization of dietary amino acids (AAs) and minerals in juvenile grass carp. Five experimental diets consisted of graded levels of PA (0.2, 4.7, 9.5, 19.1 and 38.3g kg(-1), named as P0, P5, P10, P20 and P40). Triplicate groups of fish (initial weight, 22.37 +/- 0.16g) were fed twice daily (08:00 and 16:00h). The crude protein content in whole body significantly (p<.05) decreased in fish fed with 19.1 and 38.3g PA kg(-1) diet. Supplemental PA (>4.7g kg(-1)) significantly reduced the apparent digestibility coefficient (ADC) of AAs (Asp, Thr, Ser, Glu, Gly, Ala, Cys, Val, Met, Ile, Leu, Phe, Lys, Pro, His and Arg) and the ADC of minerals (P, Ca, Mg, Zn, Cu, Fe and Mn) in grass carp. The contents of minerals (P, Ca, Mg and Zn) in whole body and bone were also found to be significantly reduced in dietary PA > 4.7g kg(-1), while the bone ash, serum Alkp and Zn contents were found to be significantly decreased when the PA supplementation level was above 9.5g kg(-1), and the contents of serum Ca and Mg were found to be markedly altered in higher PA-supplemented groups. The results indicated that supplemental PA decreased the apparent digestibility and utilization of AAs and minerals, and thus reduced the feed utilization of grass carp, suggesting that the level of total PA should be below 4.7g kg(-1) in grass carp diet.