Using supplemental amino acids to lower protein levels in Jian carp diets by Juyun He1, Karthik Masagounder2 and Mingchun Ren3 Evonik Degussa Co, Ltd, Guangzhou Branch, China Evonik Operations GmbH, Germany 3 Wuxi Freshwater Fisheries Research Centre, Nanjing Agricultural University, China
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t has been a common practice in the swine and poultry industries to reduce dietary crude protein (CP) levels with the use of supplemental amino acids while following an ideal protein concept (Htoo et al., 2007; Berres et al., 2010; Powell et al., 2011; Wu, 2014). In fish species such as rainbow trout (Oncorhynchus mykiss) (Gaylord & Barrows, 2009) and Nile tilapia (Oreochromis niloticus) (Botaro et al., 2007), low-protein diets with limiting essential amino acids (EAA) supplementation did not negatively affect growth performance, while showing environmental benefits (Liu et al. 2009). Using the diets formulated with fishmeal as the main protein source and methionine supplementation showed that dietary protein levels higher than 34.1 percent is not needed for juvenile Jian carp, a variant of the common carp (Cyprinus carpio). Common carp contributes towards ~50 percent of the total annual production of farmed carp (Ji et al., 2015). Commercial feed samples (n=39) of juvenile common carp collected in China during 2018-2019 showed high dietary protein levels (~36%). Evonik, in collaboration with Dr Mingchun Ren of the Freshwater Fisheries Research Centre CAFS (FFRC), wanted to investigate the effects of increasing EAA supplementation on
Figure 1: Total ammonia nitrogen (mg/kg body weight) discharged into water over 15 hours after the last meal
the success of sparing intact protein sources and reducing dietary protein levels in juvenile Jian carp, based on growth and nitrogen utilisation.
Materials and methods
Feeding trial: The study evaluated five dietary treatments: a positive control (PC, D1, 37.84% protein) was formulated to reflect a typical high protein practical diet which could meet all the EAA requirement through intact protein sources and DL-Met supplementation alone. Diets 2-4 were formulated to contain 34.04%, 31.87%, 29.90% dietary protein by decreasing the levels of fishmeal, soybean meal, rapeseed meal and cottonseed meal and increasing the levels of supplemental amino acids (DL-Met, L-Lys, L-Thr, L-Ile, L-Trp and L-His) in order to meet Evonik’s EAA requirements for carp. This reduced the formulation cost of feed from US $655-to-624-per-million tonnes (mt). The formulation of the negative control (NC, D5, 28.98% protein) was similar to D4 but without EAA supplementation (See Table 1). All the diets were formulated to be iso-energic (~17.5MJ/kg gross energy). Nutrient composition and EAA profile of experimental diets are presented in Table 2. Juvenile Jian carp with an average body weight of 8.4g were randomly distributed into 20 floating cages (1m×1m×1m) at 30 fish-percage. All the cages were operated under a common concrete pond (2,000m2 area with 2m water depth) located in FFRC. Each of the five diets was randomly assigned to four of the 20 cages. Fish were fed their respective diets three times daily to apparent satiation for 10 weeks. Water temperature was at 28-32°C. Dissolved oxygen concentration was kept at 5.5mg/L. All fish in each tank were weighed every two weeks and the amount of diet given was adjusted accordingly. At the end of the feeding trial, all fish were counted and weighed in each cage to determine survival, growth rate and weight gain. After weighing, 10 fish from each cage were sampled, euthanised and stored at −20°C for measuring body composition (protein and amino acid
34 | November 2020 - International Aquafeed