The digestibility of raw materials by barramundi Lates calcarifer: Emphasis on the effect of inclusion rate on the digestibility of soybean meal and soy protein concentrate

Two digestibility experiments were done with Barramundi Lates calcarifer (average weight = 386 and 297 g for experiment 1 and 2, respectively) using indirect techniques and the reference diet substitution method. Chromium oxide was used as the inert marker and faecal material was collected by stripping. The same reference diet was used in both experiments. The first experiment determined the apparent digestibility coefficients (ADC's) of solvent extracted soybean meal (SBM) and soy protein concentrate (SPC). The SBM and SPC were tested at two dietary inclusion levels (30 or 50 %). A high-quality South American fishmeal (FM-SA) was included in the experiment for comparative purposes (30 %). The second experiment determined the ADC's of feed grade poultry by-product meal (PBM), blood meal (BLM), corn gluten meal (CGM), standard prime fishmeal (FM-P), tuna meal (FM-T), wheat (WH) and pregelatinized wheat starch (PGWS). Each of these raw materials was tested at 30 % inclusion. The results demonstrate that dry matter and energy ADC's of SBM were adversely affected by inclusion level, decreasing from 60 % to 45 % and from 72 % to 63 %, respectively when inclusion level was increased from 30 to 50 %. In contrast, the protein ADC of SBM was relatively high (>83 %) and was not affected by inclusion level. The SPC was more digestible than SBM and recorded similar protein ADC to FM-SA (95 %), irrespective of its inclusion level. However, both dry matter (74 %) and energy ADC's (82 %) of SPC were lower than those for FM-SA. The digestibility of amino acids from SBM, SPC and FM-SA were similar to their respective protein ADC's. The protein and total amino acid ADC's from FM-P were significantly higher than those for FM-T (100 % vs 88 %), however the energy ADC's of both products were close to 100 %. The dry matter, protein and energy ADC's of PBM were significantly higher than those in BLM, as was the digestibility of all individual amino acids. Dry matter digestibility of WH was very low (30 %), but far higher than PGWS (4 %). The CGM was more digestible than WH in terms of dry matter and energy ADC's, but somewhat similar in terms of protein and total amino acid digestibility. The coefficients presented here, especially the amino acid coefficients, will be useful in formulating aquafeeds for Barramundi on a digestible amino acid and energy basis as well as maximizing the dietary inclusion of products such as SBM and SPC. Two digestibility experiments were done with Barramundi Lates calcarifer (average weight = 386 and 297 g for experiment 1 and 2, respectively) using indirect techniques and the reference diet substitution method. Chromium oxide was used as the inert marker and faecal material was collected by stripping. The same reference diet was used in both experiments. The first experiment determined the apparent digestibility coefficients (ADC's) of solvent extracted soybean meal (SBM) and soy protein concentrate (SPC). The SBM and SPC were tested at two dietary inclusion levels (30 or 50 %). A high-quality South American fishmeal (FM-SA) was included in the experiment for comparative purposes (30 %). The second experiment determined the ADC's of feed grade poultry by-product meal (PBM), blood meal (BLM), corn gluten meal (CGM), standard prime fishmeal (FM-P), tuna meal (FM-T), wheat (WH) and pregelatinized wheat starch (PGWS). Each of these raw materials was tested at 30 % inclusion. The results demonstrate that dry matter and energy ADC's of SBM were adversely affected by inclusion level, decreasing from 60 % to 45 % and from 72 % to 63 %, respectively when inclusion level was increased from 30 to 50 %. In contrast, the protein ADC of SBM was relatively high (>83 %) and was not affected by inclusion level. The SPC was more digestible than SBM and recorded similar protein ADC to FM-SA (95 %), irrespective of its inclusion level. However, both dry matter (74 %) and energy ADC's (82 %) of SPC were lower than those for FM-SA. The digestibility of amino acids from SBM, SPC and FM-SA were similar to their respective protein ADC's. The protein and total amino acid ADC's from FM-P were significantly higher than those for FM-T (100 % vs 88 %), however the energy ADC's of both products were close to 100 %. The dry matter, protein and energy ADC's of PBM were significantly higher than those in BLM, as was the digestibility of all individual amino acids. Dry matter digestibility of WH was very low (30 %), but far higher than PGWS (4 %). The CGM was more digestible than WH in terms of dry matter and energy ADC's, but somewhat similar in terms of protein and total amino acid digestibility. The coefficients presented here, especially the amino acid coefficients, will be useful in formulating aquafeeds for Barramundi on a digestible amino acid and energy basis as well as maximizing the dietary inclusion of products such as SBM and SPC.

Automated summary

Two digestibility experiments were conducted with Barramundi Lates calcarifer using indirect techniques and the reference diet substitution method. Results showed that the dry matter and energy ADC's of SBM were adversely affected by inclusion level, while the protein ADC remained relatively high. SPC was found to be more digestible than SBM.