CURRENT STATUS OF PROTEIN: ENERGY RATIO RESEARCH IN

PENAEID SHRIMP NUTRITION

Dr. Joe M. FoxMARI-5314

Background• Of all the issues important to shrimp nutrition,

reduction of feed cost with concomitant increased feed performance are most desirable.

• Because feed cost is primarily associated with protein and energy levels, the issue is therefore one of “quality.”

• This “quality” refers to how well protein and energy sources are digested, absorbed across the gut and assimilated into tissue growth.

• Use of poor quality protein or energy in feeds presents high potential for reduced efficiency of growth and increased excretion of nitrogenous waste products into the culture medium and/or receiving stream.

Protein “Level” or “Requirement”?

• Past research on requirement of protein by shrimp has largely focused on feed protein concentration (%) and failed to address digestibility and feed consumption as factors

• Problem: theoretically, low dietary protein levels can be compensated for by high quality protein (increased digestibilty) and/or higher feed ingestion rate

• Instead, requirement research now focuses on how much protein must be assimilated on a daily basis to maximize growth

• Protein “requirement” has been shown to actually decrease with increased body weight, irrespective of dietary protein level (Kureshy and Davis, 2002)

Protein Efficiency

• As mentioned, cost of protein is really an efficiency issue: how well is dietary protein utilized for tissue deposition? Various metrics (Capuzzo 1983):• Protein efficiency ratio (PER): wet weight gain per

unit dry weight protein fed• Protein utilization efficiency (PUE): dry weight protein

deposition in tissues per unit dry weight protein fed• Net protein utilization (NPU): protein retained after

losses per unit dry weight protein ingested• PER/PUE shown to increase with decreased level of

dietary protein (only if non protein energy is in excess)

Protein as Energy• As mentioned, optimization of dietary protein for

tissue (growth and maintenance) is essential.• Problem?: protein can be used as a source of energy

by crustaceans (Wolvekamp and Waterman, 1960; Cowey and Sargent, 1972)

• Indicated by their limited ability to store lipids and COH (Dall and Smith, 1986)

• Inference: the use of protein for tissue growth is optimized when its requirement as an energy source is minimized

• Result: caused research to focus on bioenergetics and optimization of non-protein energy sources

Energy Issue• Crustacean bioenergetics was investigated in

some detail in the late ’70s by Logan and Epifanio (1978) and Capuzzo (1979)

• Why? Fundamental differences exist in crustacean energy partitioning (vs. aquatic vertebrates): • buoyancy in aquatic medium• waste energy losses are lower (NH3-N as main

species)• metabolic/heat losses due to molting = variable

energy demand

Non-protein Energy

• Other problems exist in optimization of dietary protein level using non-protein energy sources:

• dietary lipid concentration limited to < 10-12% (Deshimaru and Kuroki, 1974; Bautista, 1986) due to pellet stability, palatability issues

• Also, shrimp are unable to efficiently utilize simple carbohydrates (e.g., monomers of glucose; (Andrews et al., 1972; Sick and Andrews, 1973; Alava and Pascual, 1987; Shiau and Peng, 1992)

Carbohydrates as Energy Sources

• This leaves “complex” carbohydrates as the most practical source of non-protein energy in balanced formulations (Cuzon and Guillaume, 1989)

• Available from a variety of different sources (Deshimaru and Yone, 1978; Abdel-Rahman et al., 1979; Pascual et al., 1983; Alava and Pascual, 1987)

• Problem: they have variable digestibility coefficients (Forster and Gabbot, 1971; Capuzzo and Lancaster, 1979; Akiyama et al., 1992; Cousin et al., 1993)

• Wheat starch is most common carbohydrate used in research formulations due to high digestibility (92%; (Cousin, 1991)

Measuring Energy Efficiency-I• Ingestion of feed by aquatic organisms results in an

increase in oxygen consumption (metabolic rate) and heat production (increment) reflective of catabolism of biochemical substrates (e.g., protein, carbohydrate, etc.)

• Referred to as specific dynamic action• Energy lost through catabolic processes may vary with

variable utilization of dietary components• Results in substantial differences in energetic efficiencies

and, ultimately, significant differences in energy partitioning towards growth

• Energetic efficiencies are also influenced by a variety of abiotic and somatic factors (Sedgwick, 1979a, Bartley et al., 1980; Rosas et al., 2002)

Energy Efficiency-II

• Metabolizable energy (ME) is normally considered the best metric of energy efficiency in terrestrial systems

• However: difficult to determine in aquatics due to inherent inability to quantify losses (i.e., quantify waste)

• Energy efficiency of feeds for most aquatics is relegated to apparent digestible energy:

• ADE = IE – FE• For finfish, DE approximates ME (Lovell, 1998) and is a

reasonable indicator of quality of energy sources in feeds• Problem: DE could be highly variable depending upon

trophic level (herbivore, carnivore, omnivore)

Energy Efficiency-III

• A method for estimating ME in shrimp feeds was proposed by Cuzon and Guillaume (1997) and involved using physiological fuel values for carbohydrate, lipid and protein (Brett and Groves, 1979)

• PFV x dietary levels of nutrients x ADC ME • Other authors (e.g., Lim et al., 1997) have used different

PFVs (as per Maynard and Loosli, 1964)• Other approaches: GE via bomb calorimetry in

conjunction with predetermined coefficients of apparent digestibility = DE (Aranyakananda and Lawrence, 1996) or indirect methods (i.e., chromic oxide)

Protein:Energy• Gross energy (GE) of most crustacean feeds ranges

from 3-4 kcal per g of feed (Cuzon and Guillaume, 1997), >3,500 kcal/kg (Alava and Lim, 1983)

• Because GE has little variation, knowledge of digestibility coefficients for all dietary energy sources is required to establish an appropriate relationship between dietary protein and energy content

• Relationship commonly referred to as P/E or DE:P, etc.

• Published dietary relationships between protein and energy are quite multiconventional and, therefore, confusing

Protein:Energy• As mentioned, optimum energy requirement should be

determined in conjunction with a minimum dietary protein level in order to reduce feed cost (COH is least-cost energy)

• Possible outcome: fairly narrow range of DE:P: Why?• High DE:P could lower ingestion/consumption rate of

dietary protein (presumed, opposite actually shown) • Low DE:P could increase protein catabolism (shown)• Either situation could ultimately result in reduced

weight gain• Additional question: does DE:P really affect

consumption?

Research Efforts on P/E

• Past research efforts have largely focused on finding most appropriate COH source allowing best protein sparing effect

• Most early studies did not differentiate between GE, DE and ME

• Other relevant issues:• Variable COH and PRO levels• PRO constant, COH variable w/various sources• FCR used to report growth efficiency, but feed consumption not

quantified• Digestibility coefficients not reported

• GE of feeds estimated, not determined

Research Efforts on P/E• 29.86 mg CP/kJ for P. monodon using low/high PRO

feeds with various mixtures of CHO and lipid (Bautista, 1986)

• 26.8 mg CP/kJ for P. monodon using glucose, sucrose and trehalose (Alava and Pascual, 1987)

• Improvement came with use of isonitrogenous diets (Hajra et al., 1988): for isonitrogenous high-protein feeds, (46% CP), NPU and FE were optimized for P. monodon at 26.80 mg CP/kJ

• 25.26 mg CP/kJ for P. monodon using two protein and six energy levels (energy calculated; Shiau and Chou, 1991)

Research Efforts on P/E

• 23.88 mg CP/kJ for Litopenaeus vannamei (Cousin et al., 1991)

• 26-28 mg CP/kJ for P. monodon using glucose, dextrin, starch (Shiau and Peng, 1992)

• 35.83 mg CP/kJ for P. monodon (Chuntapa et al., 1999)

• 25 mJ/kg DE:DP for Litopenaeus stylirostris (Aquacop et al., 1996)

• General conclusion: P/E for L. vannamei could be lower than that for P. monodon; COH appears to spare protein

P/E-Related Research: Protein Metabolism

• As mentioned, shrimp don’t store COH and lipid well• Energy partitioning heavily influenced by energetic status

(e.g., molting, osmoregulation, etc.) and dietary energy sources

• Consumption of high protein feeds results in high levels of hemolymph protein

• This protein used either as an energy source (gluconeogenesis pathway) or broken down into FAA for osmoregulation

• Proteins are then typically deaminated or transaminated, resulting in increased NH3

Related Research: PRO:CHO Interaction

• Rosas et al. (2001) observed that a very low dietary COH level (1%) could induce PEPCK activity (key in regulation of gluconeogenesis)

• Metabolic use of protein measured by: • level of NH3 excretion (Dall and Smith, 1986; Lei et al., 1989;

Taboada et al., 1998) or

• post-prandial nitrogen excretion (Claybrook, 1983; Rosas et al., 2002)

• High dietary COH (>33%) is prohibitive due to saturation of -amylase in the HP limits glucose production, HP also saturated with glycogen (Rosas et al., 2002)

Related Research:Low Salinity COH Interaction

• At low salinity, dietary proteins are used as a source of osmoregulatory amino acids• Low salinities favor protein metabolism (measured

through O/N)

• Apparent heat increment increases (O2 consumption)

• GDH activity increases due to increased NH3

• Result: at low salinity, low COH diets improve growth (Rosas et al., 2001)

Research RecommendationsThere is no best way to do this type of work due to

the interactions of feed intake, energy/protein utilization, etc.; however:

• Use of single, standard protein source in trials to maintain constant amino acid profile of protein

• Digestibility coefficients of both protein and non-protein energy sources determined as part of study

• Experimental diets low protein/isonitrogenous, ME values estimated from GE (bomb calorimetry) x digestibility coefficients or DE (indirect)

• Non-protein energy sources should be highly digestible• Ingestion of protein/COH estimated to yield daily

protein/energy intake rates

P/E Research

• High attractability and feeding stimulation rate of experimental diets

• Look at whole body energy retention

• Feed to satiation or slightly less

• High rate of passage implies > automated multiple feedings

• Evaluate abiotic interactions (e.g., temperature, salinity)

• Evaluate somatic issues: age/weight, molt status

Conclusions

• Identifying P/E for marine penaeid shrimp is a difficult proposition due to their ability to utilize various sources of energy

• Plenty of interaction• Bottom line for farmers: cost per unit protein

ingested• As can be seen, we still have a long way to go.