Reevaluation of the choline requirement of fingerling channel catfish (Ictalurus punctatus) and determination of the availability of choline in common feed ingredients

The dietary choline requirement of fingering channel catfish in the presence of 2-amino-2-methyl-1-propanol, a specific inhibitor of choline biosynthesis, was reevaluated. The correlation between dietary choline and liver choline was used to estimate the choline availability in seven common feed ingredients for channel catfish. Initially, 10 semipurified diets were fed to fingerling channel catfish for 8 weeks: three contained graded levels of choline at 0, 200 and 400 mg/kg diet and no inhibitor, seven others contained 0.3% 2-amino-2-methyl-1-propanol and increasing levels of choline at 0, 200, 300, 400, 500, 600 and 700 mg/kg diet. Two linear regression equations were obtained based on the data of liver choline vs. dietary choline. The regression equation for the three inhibitor-free diets had a slope of 0.87. The regression equation for the seven inhibitor-containing diets had a slope of 1.02. These data indicate that: (1) the synthesis of choline was blocked when the inhibitor was added; and (2) in the absence of the inhibitor, adequate choline biosynthesis was observed to meet the metabolic needs of this species. In the second 8-week experiment, three semipurified diets, containing 0.3% 2-amino-2-methyl-1-propanol, and 0, 200 and 400 mg choline/kg diet, were used to generate a standard curve for determining the choline availability in seven test diets containing the following common feed ingredients, corn meal (CM), cooked corn meal (CCM), cottonseed meal (CSM), soybean meal (SBM), wheat middlings (WM), menhaden fish meal (MFM), and meat and bone/blood meal (MBM). Based on liver choline data, choline availability values were 69,78, 55,74, 54, 92 and 90% in CM, CCM, CSM, SBM, WM, MFM and MBM, respectively. The available choline in typical catfish feed formulations is more than sufficient to meet the choline needs of this species. This observation along with evidence for endogenous choline synthesis indicates that choline supplementation of commercial catfish feeds no longer appears warranted.