Apparent digestibility coefficients and amino acid availability of common protein ingredients in the diets of bullfrog, Rana (Lithobates) catesbeiana

Farming of bullfrog Rana (Lithobates) catesbeiana has been expanding remarkably in the past decades to support an emerging food delicacy in southeastern China. However, lack of understanding of nutrient availability in common protein ingredients restricts precise formulation of bullfrog feeds, partially because of difficulties in collection of fecal material from bullfrog. Therefore, we carefully designed an apparatus that allows feces of bullfrogs to be collected while minimizing leaching in water and reducing stress imposed to the animals. By using this apparatus, a study was conducted to determine apparent digestibility coefficients (ADCs) of dry matter, crude protein, gross energy, and availability of phosphorus and amino acids in practical feed ingredients for bullfrog. Test ingredients included white fishmeal (WFM), brown fishmeal (BFM), porcine meat and bone meal (PMBM), poultry by-product meal (PBM), feather meal (FEM), soybean meal (SBM), peanut meal (PNM), cottonseed meal (CSM) and rapeseed meal (RSM). A reference diet and test diets that included 70% reference diet and 30% of the test feed ingredients were used with 0.5% chromic oxide included as a digestibility indicator. Bullfrogs (153 +/- 3.14 g) were cultured in indoor aquaria (68 x 38 x 38 cm) equipped with the apparatus for fecal collection, and each aquarium was stocked with 15 specimens. ADCs of dry matter and energy were high (above 80%) in WFM and BFM, and low (below 40%) in CSM and RSM. ADCs of crude protein in those tested feed ingredients varied from 60.7 to 89.8%. WFM (89.8%), BFM (87.6%), SBM (83.3%), PNM (82.1%), PMBM (78.0%), PBM (77.6%) were more digestible protein feedstuffs, compared to RSM (69.5%), CSM (67.5%), and FEM (60.7%). In addition, the highest availability for phosphorus (84.8%) was observed in WFM, and the lowest value was found in FEM (63.6%). This study also demonstrated that phosphorus availability in the other seven ingredients ranged from 71.9 to 84.0%, indicating that phosphorus in BFM, PMBM, PBM, SBM, PNM, CSM and RSM could also be utilized by the bullfrog. Amino acid availability for the test ingredients followed a similar pattern to ADCs of crude protein, in which values for fishmeal were generally higher (P < 0.05) than those of other protein ingredients. Among all plant meals, the amino acid availability values in soybean meal were significantly (P < 0.05) higher than those in PNM, CSM and RSM. The availability of most amino acids in FEM was the lowest (P < 0.05) among all tested ingredients. In conclusion, PMBM, PBM, SBM and PNM may be good sources of available protein and amino acids, and should be promising substitutes for fishmeal in diets for bullfrogs. (C) 2014 Elsevier B.V. All rights reserved.