Lecture 19 nutrition

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 (not good for fish sales!)

• corn gluten meal is high in protein (60%) and contains high levels of MET (excellent for formulation)

• 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 destroyed by steam pelleting or extrusion

• 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 acidPhytic 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”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, OTC)

• OTC commerically available as “medicated” fish (shrimp) feed, 1,500 mg/kg

• Must not feed medicated diets within 14-21 days from slaughter/harvest (more regulations!)

Attractants

• Attractants are materials added to feeds to serve as intake (feeding) stimulants

• They are cost effective since they cause shrimp/fish to eat feeds that otherwise would not be attractive (consumed)

• Facilitates 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)