Transcript Review: Protein and Energy in Shrimp Feeds

CURRENT STATUS OF PROTEIN:
ENERGY RATIO RESEARCH IN
PENAEID SHRIMP NUTRITION
Dr. Joe M. Fox
MARI-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 Recommendations
There 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.