The high CP levels and CP:energy ratio in Exp. 2may be the main reason
why the reduction in the digestibility of protein and several amino
acids by the addition of HPDDG to diets appeared to cause no adverse
effects on growth performance or nitrogen retention of the fish. Moreover,
there was no reduction in the digestibility of methionine, and an
increase in cysteine digestibility in fish fed the highest HPDDG level.
The high digestibility of cysteine in the HPDDG diet indicates lenient
heat treatment during production of HPDDG because excessive heat
treatment is particularly detrimental to cysteine digestibility