Post on 08-Feb-2016
description
Feed Ingredients and Physical Characteristics
Formulating Feeds
• Nutritionally complete feeds should be used whenever natural foods are absent or where natural foods only make a small contribution to nutrition
• when substantial amounts of natural productivity are available, supplemental feeds don’t need to contain all essential nutrients
• we will focus on nutritionally-complete feeds
Nutrient Requirements
• Most requirements for nutrients that have been published focus on juvenile fish/shrimp
• many represent single lab experiments, unchallenged, unsupported by others
• optimum performance can be affected by management, environmental factors and fish/shrimp size
• in formulating diets for a species for which nutrient requirements are unknown, those for a related species are used
Nutrient Requirements• Most variation among aquatic species can be associated
with whether the animals are: 1) coldwater vs. warmwater; 2) freshwater or marine; 3) finfish vs. crustaceans
• values in nutrient requirement tables only represent minima, don’t allow for processing or storage losses
• AA’s, minerals stable wrt heat, moisture, oxidation• vitamins and lipids are not stable (affected by heat,
oxidation, light, moisture, etc.; store in cool area)• 50% of ascorbic acid is lost in processing, half-life of 2-3
months in storage
Physical Properties• Ground meals are not suitable
for feeding to aquatic animals due to poor ingestion, feed conversion, and reduced water quality
• pellets need to be stable in water until consumed by the target animal
• good pellet stability required for slow-feeding species such as shrimp
• particle size is important to insure appropriate consumption
various sizes of fish feed particles
Physical Properties
• Diet texture is also important for some aquatic species: some prefer moist vs. dry feeds (e.g., eels, salmon)
• sometimes farmers prefer floating pellets, allowing confirmation of ingestion
• shrimp prefer sinking pellets (density greater than that of water, 1 g/cm3)
• floating feed can be detrimental with respect to consumption by competitors
Practical Feed Ingredients
• Ingredients used in practical fish/shrimp feeds can be classified as: protein sources (including amino acids) energy sources (COH)lipid sources (also essential fatty acids)vitamin supplements/premixesmineral supplements/premixesgrowth/pigment enhancersingredients improving palatabilityingredients improving preservation/storage
Fish Meal (FM)• If made from good quality whole
fish, properly processed, it is the highest quality protein source commonly available
• rich source also of energy and minerals
• highly digestible, highly palatable, also serves as an attractant
• usually contains about 65% protein, that is around 80% digestible
• high in LYS, MET (deficient in plant sources)
Fish Meal (FM)
• Fish meal also contains 1-2.5% n-6 fatty acids, essential to many fish and all shrimp
• if made from byproducts, its quality is not as good as trawler-caught
• only problem observed: high ash content can sometimes result in mineral imbalance
• used sparingly because of high cost• can be partially replaced by soybean meal and
other animal meals
Fish Meal (FM)
• When using FM, one must remember that it cannot be stored forever
• can rancidify due to high lipid content• further, not all FM is created equal• some types (menhaden) appear to be superior to others
(sardine meal)• FM must be very well ground and sieved to help
remove indigestible parts• big producer countries are USA, Peru, Mexico,
Ecuador
Soybean Meal (SBM)• Soybean meal has one of the
best essential amino acid profiles of all protein-rich plant feedstuffs
• Table 5.3 (Lovell)• SBM does not appear to be
deficient in any EAA for catfish• can be deficient wrt eel, because
their MET/CYS requirement is twice that of catfish
• some fish find SBM unpalatable, for this reason maximum levels are suggested
Soybean Meal (SBM)• Soybean meal is commonly
used to spare fish meal, however, only to a point
• true for chinook, but not for catfish
• shrimp will consume high SBM feeds, but diet must be supplemented with fish meal at some point
• another problem involves losses in energy, minerals and lipids in diets where SBM replaces FM or other animal byproduct proteins soy protein
Soybean Meal (SBM)• Another variety of soybean meal is known as “de-
hulled”• de-hulled soybean meal contains 25% less ME,
85% less available P and 90% less n-3 FA’s than anchovy meal
• soybeans also contain trypsin-inhibitors• trypsin inhibitor reduces digestibility of soy
protein by the enzyme trypsin• solution: most soybeans are roasted prior to
milling (destroys inhibitor)
Full-fat Soybeans
• Full fat soybean meal is different from regular SBM in that it has a full fat complement
• fat has not been solvent extracted• 18% fat vs 0.5%• often used as an energy source or for general
balancing of the formula• mainly used in salmonid (cold water) fish diets• REM: too high fat = reduced nutrient intake
Grains and By-products
• Grains are primarily used as COH sources• when whole, they contribute about 62%-72%
of dietary starch• starches are fairly well digested by warm-
water species (60-70%), but not by cold• heating via extrusion improves digestibility
by 10=15%• can also be used as binding agents
Grains and By-products• Corn is commonly used in the U.S.,
but is high in xanthophyll (a pigment), giving tissue a yellow color
• corn gluten meal is high in protein (60%) and contains high levels of MET
• rice bran often used in developing countries due to local rice production
• rice bran is a reasonable COH source, but is high in fiber and fat
• wheat gluten is a good protein source, but too expensive, often used as a binder
Animal By-products• Meat and bone meal is a byproduct of
the slaughter house• contains 50-55% crude protein• protein quality is low, so only
marginally useful and varies dependent upon meat source
• can be a good source of energy, P, TM’s• another problem: high ash content• digestibility improved by flash- or
spray-drying• poultry by-product meal (PBM) is often
used by mills also producing chicken feed
• feather meal high in protein, but indigestible
MM
MBM
Crustacean Meals
• Shrimp waste meal is a reasonably good feed ingredient, if heads are included
• otherwise, the shell is primarily chitin and of limited digestibility
• the ammonia in chitin accounts for about 10-15% of the nitrogen in whole meal
• also a reasonable source of n-3 fatty acids, cholestrerol and astaxanthin (carotenoid)
• highly palatable and often serves as an attractant in feeds at 1-2%
• others: krill meal, Artemia meal krill meal
Fats and Oils• Used as energy sources, provide
essential fatty acids, attractant, coating of pellet to reduce abrasion
• both animal and plant fats can be used, animal fats cheaper, better attractants
• marine lipids often added as oils if FM level is low (otherwise no source of marine FA’s)
• sources: menhaden, shark, cod liver
• must be careful in storage of oil, feeds with oils due to rancidification
menhaden oil
Fibrous Feedstuffs• Most monogastric animals
(e.g., fish) do not digest fibrous feedstuffs well
• it is unlikely that adding fiber to diets already with more than 3-5% will have any beneficial effect
• high fiber content reduces binding capacity of feeds, inhibits intake (due to reduced palatability), increases rate of passage and waste production
• sources: bransrice kernel
Binding Agents
• Binding agents are really needed for pelletized feeds, but not necessarily for extruded feeds (we discuss this later)
• in extruded feeds, all ingredients are gelatinized by high temperature and bind together well as a result of the process
• show Table 5.4 (Lovell, page 118)
Binding Agents
• most organic binders are good for about 30 min of submergence
• starch is often used at over 10%, however it will hydrate and swell the pellet
• chemical binders (e.g., Basfin) have good binding potential, form cross-linkages with COH and PRO, but are toxic
Non-nutrient Diet Components
Basic Facts
• In addition to the essential nutrients, feeds may contain organic and inorganic materials that have various effects on aquatic species:
• beneficial, detrimental or negligible• they can affect growth, health or the processed
product• may be naturally occurring, intentionally or
unintentionally added• can be produced via microbial growth
Toxins and Antimetabolites
• The more important toxins affecting animal feeding are those associated with molds
• these are called “mycotoxins”• three important genera are Aspergillus, Penicillium
and Fusarium• they exist and grow anywhere as long as there is
enough COH substrate, no less than 14% moisture, adequate temperature, oxygen
• usually produced in feedstuffs prior to harvest, but also result from poor storage
Aflatoxin
• Aflatoxin is the mycotoxin of greatest concern in feeding of culture species
• both outright toxic and carcinogenic• liver (hepatoma) and blood clotting problems• rainbow trout are highly sensitive at 1 ug/kg
exposure• traditionally, sources include corn, cottonseed and
peanuts• aflatoxin contamination varies year to year
Ochratoxin
• These are compounds produced by Aspergillus and Penicillium molds
• widely found in nature• typically associated with kidney toxicity• toxic level is 4.7 mg/kg in diet• other mold toxins have been found in warm-blooded
animals, but not in fish• most mold toxins also destroy nutrients in feeds• example: Pseudomonas can separate glutamic acid
from folic acid, making it ineffective
Microbial Toxins in Commercial Fish/shrimp Feeds• Usually not known that the feed is contaminated!• commercially-processed feeds are less likely to have
these toxins• screened against international transport and by feed
manufacturers by law• must contain less than 20 ppb• up to manufacturer to require testing• not all destroyed by steam pelleting/extrusion (spores)• presence in feeds reduced by proprionic acid
Histamine, etc.
• This is a toxic compound found in fish meal, a typical feed ingredient
• results from bacterial removal of COOH (carboxylic acid) from the EAA histidine
• comes from improper storage of raw fish prior to production of fish meal
• causes a reduction in growth rate• usually comes from “dark” meat portion of fish• other fish meal toxin is “gizzerosine”
Phytic Acid, Gossypol• Phytic acid is an organic molecule related to inositol• integral component of plant feedstuffs and holds 60-
70% of the phosphorus• problem is, it’s poorly available to fish• reduces availability of zinc• “gossypol” is a component of pigment lands in the
cotton plant• limits availability of cottonseed meal used in feeds
(suppresses growth rate and causes liver damage)
Fish Oils, Fiber• Marine fish oils contain 20-25% PUFA’s• the “autoxidation” of PUFA’s results in formation of large
numbers of free radicals and peroxide compounds• these are toxic due to reaction with other nutrients, limiting
availability• also cause cellular/subcellular damage• severity of effect reduced by Vit E• fiber can also be mildly toxic as it increases rate of gut
passage• high rate of passage causes reduced availability of nutrients
Diet Additives: Hormones
• Hormonal control used to produce mono sex cultures of fish
• reduces reproduction/increases growth• ex. Androgenic steroids (ethyltestosterone) fed to
tilapia fry = 90% males• does not work the same on all fish• 17-alpha-methyltestosterone improves growth and
survival in salmonids• andorgenic better than estrogenic• used as implants in cattle
Pellet Binders• Steam pelleted aquatic feeds,
especially those fed to shrimp, contain binders
• these are used for improving water stability (reduced leaching and nutrient loss)
• two different types: organic matrix (lignosulfonates or polysaccharides)
• other type: chemical compounds (sodium hexametaphosphate)
• no evidence of detrimental effect on aquaculture species
Antibiotics• Some feeds can be formulated with antibiotics
for treatment of Vibriosis, other bacterial infections
• three antibiotics approved in U.S. are sulfadimethoxine, sulfamerazine and terrymycin (oxytetracycline)
• oxytet commerically available as “medicated” shrimp feed, 1,500 mg/kg
• must not feed medicated diets within 14-21 days from slaughter/harvest
Attractants
• Attractants are materials added to feeds to serve as intake stimulants
• they are cost effective since they cause shrimp/fish to eat feeds that otherwise would not be attractive (consumed)
• allows inclusion of by-products• usual inclusion level is around 0.5-1.0 %, largely due to
cost• examples: krill meal, Artemia meal, fish oils, fish meal• sometimes used to reduce protein content of feed (but
most also feed more frequently)
Antioxidants
• Oxidation of lipids in feeds or feedstuffs can cause reduction of the nutritional value of certain lipids and vitamins
• it can also result in production of toxic free radicals and peroxides (REM?)
• potential for formation of these toxic compounds reduced by synthetic compounds such as BHA (butylated hydroxyanisole, BHT (butylated hydroxytoluene)
• also via natural compounds (Vit E)