Amino acid availability of selected plant products and fish meal for American alligator (Alligator mississippiensis)

Digestibility trials were conducted to determine the amino acid availability of selected ingredients (corn grain, soybean meal, soy protein concentrate, wheat gluten, and menhaden fish meal) fed to American alligator at inclusion levels of 30% or 45% of the diet. Apparent crude protein digestibility of soybean meal and soy protein concentrate was significantly reduced at the higher dietary inclusion level, while crude protein digestibility of wheat gluten was unaffected (P>0.05). Energy digestibility of soybean meal also was significantly reduced at the 45% inclusion level, but energy digestibility of soy protein concentrate and energy digestibility of wheat gluten did not change (P>0.05) at either inclusion level. Crude protein digestibility of yellow corn grain was not affected (P>0.05) by corn inclusion level, but energy digestibility of corn was reduced (P<0.05) at 45% corn inclusion. Neither crude protein digestibility nor energy digestibility of menhaden fish meal were affected by dietary inclusion level in two size classes of alligator tested. One or more statistically significant differences in availability of individual amino acids were observed for some ingredients fed at the two dietary inclusion levels. In the majority of cases where a statistically significant difference occurred, the availability of the affected amino acid was significantly lower at 45% ingredient inclusion than at 30% inclusion. Among presumed dietary essential amino acids, this was the case for arginine, histidine and phenylalanine in corn and menhaden fish meal; lysine in soy protein concentrate, wheat gluten, and menhaden fish meal; and isoleucine, leucine, and valine in menhaden fish meal fed to larger alligators. In corn and menhaden fish meal fed to smaller alligators, apparent availability of methionine was higher (P<0.05) at the 45% ingredient inclusion level than at 30% inclusion. No differences (P>0.05) were observed in the availability of any amino acid in soybean meal fed at 30% or 45% of the diet. Results indicated that American alligator efficiently digested crude protein and energy in an assortment of plant products of varied chemical composition which could be used as alternatives to animal protein in compounded diets. Availability of dietary essential amino acids also was usually high (often greater than 90%) when these ingredients were provided at levels of 30–45% of the diet.