Yuexing Zhang defended his PhD thesis on December 2nd 2011

Ane Gro Siri Skjelfjord

Optimal use of plant protein concentrates in extruded feeds for carnivorous fish

Abstract from the thesis - PhD thesis 2011:53

Author: Yuexing Zhang

The main objective of the research presented in this thesis was to evaluate muItiple amino acidsupplemented plant protein concentrates as the main protein source in diets for carnivorous fish. This objective was approached experimentally by: I) Determining the effects of using plant protein concentrates to provide 30 %, 50 %, and 95 % of total protein in extruded diets for rainbow trout and black sea bream on growth performance, feed utilization, and nutrient digestibility and retention; 2) Examining if combinations of different plant protein concentrates diminishes the negative effects of anti-nutritional factors associated with single plant protein sources when fed to carnivorous fish, thereby facilitating higher dietary plant protein inclusions; 3) Evaluating the effects of dietary inclusion of plant protein concentrates on fish physiology and health; 4) Assessing the efficiency of pre-treatment of plant protein concentrates with phytase to improve utilization of minerals and macronutrients in rainbow trout; 5) Quantifying the changes in loss of nutrients to the environment by replacing high-quality fish meal with untreated or dephytinized plant protein concentrates. The dietary plant protein concentrates used in this thesis were all supplemented with multiple limiting amino acids and taurine.

Four experiments were conducted, and the results are reported in four papers. Paper I (Optimal inclusion of lupin and pea protein concentrates in extruded diets for rainbow trout (Oncorhynchus mykiss)) focuses on the response of rainbow trout to nine extruded diets. These diets included eight plant protein based diets formulated using four mixtures of lupin (LPC) and pea protein concentrates (PPC) (L/P ratio, 3:0, 2:1, 1:2 and 0:3) with two dietary inclusion levels (300 or 500 g plant protein kg-1 dietary protein) and one diet using LT-fish meal as the sole protein source (FM diet). The same nine diets, but with a lower level of oil coating, were also studied in black sea bream in Paper II (Mixtures of lupin and pea protein concentrates can efficiently replace high-quality fish meal in extruded diet for juvenile black sea bream (Acanthopagrus schlegeli)). In Paper III (Optimizing plant protein combinations in fish meal-free diets for rainbow trout (Oncorhynchus mykiss) by a mixture model) three plant protein premixtures (P-MIX, C-MIX, and S-MIX) were prepared by mixing four protein concentrates. These were pea protein concentrates (PPC), canola protein concentrate (CPC), potato protein concentrate, and soy protein concentrate (SPC). Seven plant protein based diets were formulated based on a mixture design using P-MIX, C-MIX, and S-MIX alone or in combinations to provide > 95% of the dietary protein. These diets were supplemented with 5% krill products as feeding attractant. One diet using LT-fish meal as the sole protein source (FM diet) was also produced. All diets were designed to contain equal amounts of digestible protein and digestible energy, and fed to rainbow trout. In Paper IV (Incubation of soy protein concentrate with phytase improves the nutritional value of a fish meal-free diet for rainbow trout (Oncorhynchus mykiss)), two of the diets from Paper III (the FM and SPC diets), and one additional experimental diet based on dephytinized SPC (DSPC diet) were fed to rainbow trout.

In Papers I and II, the trout grew from 58 to 180 g during the 62 days of feeding, and the black sea bream grew from 13 to 46 g during 60 days. No significant differences in growth rate among dietary treatments were seen for either species. The only body composition parameter significantly affected by the diets in both experiments was ash, which could be ascribed to the presence of phytic acid in the plant protein concentrates. The highest inclusion of 500 g plant protein concentrates kg-1, and the diets with the highest L/P ratio resulted in higher feed intake (FI) in black sea bream. No significant effects of diet on feed intake were observed in rainbow trout. The average feed conversion ratio (FCR) was 0.72 g dry matter intake (g gain)-1 in rainbow trout, and 1.13 g g-l in black sea bream. The diets with the highest L/P ratio resulted in higher FCR in both species, due to the higher content of non-starch polysaccharides in LPC than in PPC. In rainbow trout, the apparent digestibility of starch was reduced as a consequence of increasing dietary LPC at both inclusion levels, while the digestibility of lipid was increased with increasing dietary LPC only at high inclusion level. The diet with the highest inclusion of PPC resulted in reduced maltase activity in the intestines of both trout and sea bream. Trout fed the diet with the highest inclusion of PPC tended to have a slight decrease in mucosal fold height and a slight increase in fold fusion. The energy retentions did not significantly differ between the FM and plant protein diets in either species. Several of the plant protein-concentrate based diets resulted in similar or significantly higher nitrogen retentions in both species. The conclusion of the two papers was that any combination of essential amino acid (EAA)-fortified LPC and PPC can be efficiently used when total dietary plant protein inclusion is limited to 300 g kg-1. At higher inclusion, PPC seemed preferable. The reduced mineralization and tendencies of change in the intestinal physiology caused by the LPC and PPC require further attention.

In Papers III and IV the trout grew from 61 to 214 g during 72 days of feeding, without significant differences in weight gain among dietary treatments. In both experiments, fish fed the plant protein based diets had significantly higher feed intake, FCR, and metabolic nitrogen (N) loss than those fed the FM diet. Digestibility of most nutrients other than mineral elements, and body composition did not significantly differ from the fish fed the FM diet. The digestibility of energy and retentions of both N and energy were significantly lower in trout fed the plant concentrate diets. Fish fed diets with P-MIX, containing protein from pea and potato, exhibited inflammatory changes of mild or moderate severity in the distal intestine.

The mixture model predicted different optimal diet formulations based on different response criteria. A combination of P-MIX and C-MIX gave most efficient feed conversion. The digestibility of N and amino acids were maximized when S-MIX was used alone. The digestibility of lipid and energy were maximized by a combination of P-MIX and S-MIX. Retention of ingested N was most efficient when combining P-MIX and S-MIX, while the highest retention of digested N was obtained by a combination of P-MIX and C-MIX. Using C-MIX alone supported the highest digestibility and retention of P, and whole-body concentrations of ash, P, Ca and Mg. The reason was that the CPC in C-MIX had been incubated with phytase by the producer. Dephytinization of the SPC also resulted in significant improvements in the utilization of dietary P, as well as Ca and Mg. In addition, dephytinization of the SPC resulted in lower FCR, and increased digestible energy concentration in the diet. Both metabolic losses of N and faecal loss of energy were higher for the plant protein diets than for the FM diet, while the faecal loss of P was higher for the FM diet. Dephytinization of SPC led to a reduction in faecal and metabolic loss of N and P, and faecal loss of energy. Considerable benefits both to secure the welfare of the fish and to minimize losses of P and N into water can thus be achieved by the use of dephytinized plant protein concentrates in fish feeds.

Updated: 22.12.11
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