ANSC 2401- Animal Nutrition Exam 3 (University of Minnesota)

Lipid Definition

organic compound thatis relatively insoluble in water, but soluble in organic solvents (ether, chloroform, hexane and alcohol)

Fats

solid at room temp; animal sources (tallow)

Oils

liquid at room temp; plant sources (canola, vegetable oil)

Soxhlet Method

ether extraction of fat; a feed sample is placed above some ether and the ether runs up through the sample, dissolving the fat and removing it from the sample into a water cooled condenser; the difference between the starting sample and the end sample is the amount of fat

Crude Fat =

Lipids (true fat)
Fatty Acids (FA)
Triglycerides (TG)
Waxes
Pigments

Estimating FA from EE (ether extract)

%EE - 1 = %FA

Gas Chromatography

method of fatty acid analysis using light wavelengths

Fatty Acid

a chain of hydrocarbons ending in a carboxyl group; general formula is R-COOH; most lipids in feedstuffs are not free FA (they are found as glyceride)
Structure:
O (double bond between this O and the C)
R - C - OH

Saturated FA

do not contain any double bonds between the carbon atoms of the FA chain; found highly in animal fats

Unsaturated FA

have at least one double bond between carbon atoms of FA chain; found highly in plant fats

Classification of Unsaturated FA

according to number of C atoms and double bonds (linoleic acid is C18:2, 18 C and 2 double bonds)

Polyunsaturated FAs

unsaturated fats with 2 or more double bonds between carbons of FA chain (conventional numbering from 1 ---> 18)

Short Chain FA (VFA)

less than 6 carbons; volatilize into the air (evaporate); found in rumen fluid, large intestine (to a lesser extent), silage or other fermented feeds (fat samples need to be frozen to prevent volatilization and loss of fat); end product of fermentation; simple and complex CHO degraded to simple sugars (glucose) in the rumen, microbes then ferment glucose to obtain energy required to grow, and VFAs are the end product of fermentation (waste product of the microbes)

Process of VFA production

simple and complex CHO degraded to simple sugars (glucose) in the rumen, microbes then ferment glucose to obtain energy required to grow, and VFAs are the end product of fermentation (waste product of the microbes)

End Product of Fermentation

short chain FA

Acetic Acid

C2:0; found in forage; used for milk fat synthesis and energy

Propionic Acid

C3:0; found in grains; used for glucose production (and some lactose) and energy

Butyric Acid

C4:0; found in forage; used primarily for energy, but also some milk fat synthesis

Forages result in more

acetic acid

Low acetic acid =

low milk fat

Grains result in more

propionic acid (more efficient, less energy waste)

Medium Chain FA

7-12 carbons

Long Chain FA

> 12 C (linoleic and linolenic acid)

Linoleic Acid

C18:2; found in soy, corn, sunflower, safflower

Linolenic Acid

C18:3; found in flaxseed and linseed oil

Both linolenic and linoleic acid are

essential FAs

Essential FA

required in the diet for biological processes (the body cannot synthesize them)

Fate of VFA in Rumen

absorbed from the rumen into bloodstream; used by body tissues (accumulation of VFAs in rumen lowers pH and can cause problems)

Different Fat Sources in Animal Diets

only about a lb or so (a small portion) in the diet; feeding different sources can change the taste of milk; affects palatability; some examples are tallow, yellow grease, canola, cottonwood, flaxseed, grapeseed, safflower, soybean and sunflower oil, fish oil

Omega 3 Fatty Acids

have a double bond between the 3rd and 4th C, counting from the methyl end (18 ---> 1); examples are linolenic acid, EPA and DHA

Glyceride

glycerol backbone + FA

Triglyceride

glycerol backbone + 3 FA; energy storage in plants and animals; found primarily in cereal grains, oil seeds and animal fats; triglyceride side chains are unsaturated fatty acids

Glycerol

sugar alcohol, fermented in the rumen primarily to propionate, which is then utilized in the liver for glucose production

Glycolipids

lipids with a CHO attached; 1 FA is replaced by 1-2 sugars (typically galactose); found in forages (forages are <3% fat); almost completely degraded in the rumen

Phospholipid

one of the FA in a TG is replaced by a phosphate group bound to another complicated structure (such as choline or inositol); found in rumen bacteria (component of the cell membrane); not a major lipid in feeds

Measuring Chemical Properties of Lipids

Iodine Number
Saponification Number
Reicher-Meissl Number
Melting Point

Iodine Number

denotes degree of unsaturation of a fat or fatty acid; an unsaturated fat unites readily with iodine, two atoms of I being added for each double bond; amount of I in g that can be taken up by 100g of fat

Saponification Number

measure of the average chain length of the 3 fatty acids in a fat; when a fat is boiled with alkali (NaOH or KOH) it is split into glycerol and the alkali salt (called a soap) of the FA; number of mg of alkali required for the hydrolysis of 1 g of fat; smaller the FA molecule (short chain FA) the greater is the number of these molecules per g of fat

Reicher-Meissl (RM) Number

measures the amount of water soluble, steam VFAs (short chain) present in a fat; lard and other high molecular weight fats contain practically no VFAs (RM is near 0); butterfat contains a higher proportion contains a higher proportion of VFAs (RM is near 20-33)

Melting Point (MP)

temperature at which a fat changes from a solid to a liquid state; dependent upon chain length and degree of unsaturation of the molecule; as chain length increases the MP increases; as the number of double bonds increases, MP decreases

Benefits of Feeding Lipids

-increases the energy density of the diet (2.25 times the energy of CHOs)
-reduce dustiness of feed mixes
-produces less heat during digestion (called heat increment) than other feeds (fed more in summer)
-source of essential FA
-source of, or precursor for, cholesterol, steroid hormones, vitamin D3 and phospholipids
-carrier for fat soluble vitamins

Disadvantages of Feeding Lipids to Ruminants

-may depress feed intake
-can be unpalatable
-generally lowers milk protein %
-may lower milk fat % if fiber digestibility is decreased (feeding excess fat can poison the rumen microbes that digest fiber, which results in less digestion of acetate rich forages, which would reduce milk fat)
-not an energy source for rumen bacteria
generally toxic to rumen microbes, especially unsaturated fats (PUFA)
-fat is generally more expensive energy source than corn (only fed to high producing animals or growing animals)

Disadvantages of Feeding Lipids to Swine

-decrease pork quality
-decreased carcass leanness
-unsaturated FA make fat softer (softer pork belly)

Disadvantages of Feeding Lipids to Equine

exces weight gain in easy keepers or non-active horses

Fat Sources

Oilseeds (soybeans, flax, sunflowers)
Animal Fats (tallow from beef, lard from swine, choice white fat, which is high quality animal fat, and animal-vegetable blends)
Rumen Protected or Inert Fats (high producing lactating dairy cow; also called bypass fat; protected from microbial digestion)

Nutrient Composition of Fat Sources

Whole Cottonseed = 18-20% fat; also has fiber and CP
Whole Soybeans = 18-20% fat; also has CP (and bypass if heat treated)
Tallow = 100% fat
Rumen Inert Fats = 80-99% fat

Supplemental Fat is likely to be fed to:

high producing dairy or finishing beef

Other ruminants not fed added dietary fat

mid to late lactation dairy cows
beef cows
sheep
dairy goats

Fat Feeding Levels of Dairy Cows

<7% DM (max) (higher will impact fiber digestibility of the rumen)
2% added (max)
1 lb/cow/day for an added fat source

Fat Feeding Levels of Swine

max 6% added fat recommended based on handling characteristics
Fed to grow-finish, late gestation and lactating sows

Fat Feeding Levels of Equine

soy oil upper limit = .7g/kg BW/day
15% of diet DM as corn oil fed with no negative effects

Lipid Digestion

Hydrolysis
Biohydrogenation

Hydrolysis

initial step in the metabolism of lipids (TG, phospholipids and glycolipids) entering the rumen is the separation (hydrolysis) of glycerol from FAs; glycerol is fermented to glucose; free FA undergo biohydrogenation

Biohydrogenation

process in which rumen microbes add H to FA with double bonds (unsaturated FA0; an important mechanism through which microbes can dispose of H; if carried to completion, double bonds are converted to single bonds and the FA is now saturated; FA with double bonds are more toxic to bacteria than saturated FA

Which FA is more toxic to rumen microbes?

unsaturated FAs

Nearly all plant unsaturated FA are present in the ___configuration

cis

Incomplete Biohydrogenation

initial step is to convert from cis to trans configuration; produces a variety of trans and cis FA (unsaturated FA)

Trans Fats

many found to have adverse effects on human health, including elevated plasma cholesterol, increased risk of coronary heart disease; most common trans fat linked to health problems is elaidic acid, trans-9 18:1

Conjugated Linoleic Acids (CLAs)

cis-9, trans-11 CLA; found primarily in animal products (milk and meat) and have significant beneficial effects on human health; intermediates of linoleic biohydrogenation

Lipid Digestion an Absorption in the Small Intestine (SI)

mechanism similar to nonruminants; most of the fat enters the SI as NEFA (non-esterified fatty acids), highly saturated and bound in an insoluble complex to particulate matter (non-esterified means FA are free, or not attached to the glycerol backbone); 10-15% of lipids leaving the rumen are microbial phospholipids, the rest are saturated free FA (and small amounts of TGs and glycolipids)

Microbial phospholipids, and small amounts of TG and glycolipids, are

hydrolyzed by intestinal and pancreatic lipases

Micell formation allows

absorption of FA (requires bile and pancreatic juices)

After absorption (in the jejunum), FA are

re-esterified into TGs

Lipid Digestion and Absorption in Nonruminants

fat enters the duodenum as a coarse emulsion; bile salts emulsify fat (increases surface area); absorption of monoglycerides and free FAs occur in lower duodenum (re-esterified after absorption); ability to absorb FA decreases as chain length increases, and increases as double bonds increase

Ruminants vs. Nonruminants SI

saturated A are digested more completely in the SI of ruminants; unsaturated FA are typically digested more completely in SI of nonruminants

Composition of adipose fat is reflective of dietary fat composition and amounts of

nonruminants (no microbes to alter fat forms)

Composition of adipose fat is typically saturated for

ruminants (biohydrogenation by rumen microbes)

Adipose fat has more trans fat for

ruminants (incomplete biohydrogenation by rumen microbes)

Energy

the capacity to do work

Energy Metabolism

all the chemical exchanges that occur in the living animal or cell; originates from chemical energy of food; includes anabolism and catabolism

Anabolism

small, simple precursors are built into larger and more complex molecules (lipids, polysaccharides, proteins and nucleic acids); reactions require the input of energy, generally in the forms of free energy of hydrolysis of ATP and the reducing power of NADH and NADPH

Catabolism

degradation phase of metabolism, in which organic nutrient molecules (CHOs, fats, proteins) are converted into smaller, simpler end procudcts (lactic acid, CO2, NH3); catabolic pathways release free energy, some of which is conserved in the formation of ATP and reduced electron carriers (NADH and NADPH)

ATP

adenosine triphosphate; carriers chemical energy between metabolic pathways by serving as a shared intermediate coupling of endergonic and exergonic reactions

NAD

nicotinamide adenine dinucleotide

NADP

nicotinamide adenine dinucleotide phosphate; co-enzymes functioning as carriers of H atoms and electrons in some redox reactions (contains niacin and a B vitamin)

FAD

flavin adenine dinucleotide; co-enzyme of some redox enzymes (contains riboflavin, vitamin B2)

Energy Balance

amount of nutrients consumed is sufficient to maintain a constant body weight (nutrients below the balance will result in weight loss, amounts above will result in weight gain)

Forms of Energy

chemical (photosynthesis)
mechanical (muscle movement)
electrical (migration of ions across cell membranes)
sound
thermal

Autotrophs

create their own food; include phototrophs and lithotrophs

Phototrophs

use light energy; photosynthetic bacteria and higher plants

Lithotrophs (or chemoautotrophs)

use chemical energy; oxidize inorganic compounds like H2S, S, NH4+ and Fe2+

Heterotrophs

cannot use atmospheric CO2 and must obtain carbon from their environment in the form of complex organic molecules; include Photoheterotrophs and chemoheterotrophs

Photoheterotrophs

produce ATP from light and use organic compounds to build structures (like purple bacteria and green bacteria)

Chemoheterotrophs

produce ATP by oxidizing chemical substances (cho, protein, fat)

Importance of Energy in Animal Metabolism

-energy is required in larger amounts than any other nutrients
-energy is most often limiting in livestock production
-energy is the major cost associated with feeding animals

Energy is required for those functions of the body necessary for life:

-Mechanical work of essential muscular activity
-Chemical work such as the movement of dissolved substances against concentration gradients
-Synthesis of body constituents such as enzymes and hormones

Feed is __% if total cost

45%

Energy = __% of feed

53%; 53/100 x 45 = 23.85, so 24% of the cost of production

Usage of Energy in Animals

animals are not efficient at transforming feed energy into its own body energy; about 90% loss to the environment at each stage of the food chain

TDN

total digestible nutrient system

% TDN =

(Digestible/feed consumed) x 100 OR %DCP + %CF + %DNFA + (%DEE x 2.25)

Digestible =

protein + fiber + NFE + (fat x 2.25)

Steps in Determining TDN Vales

digestibility (feed - feces = absorbed)
computation of digestible nutrients
computation of TDN

NFE

nitrogen free extract; soluble carbs of feed such as sugar and starch; very inaccurate name; fraction has nothing to do with nitrogen; is not an extract; is determined by difference, not chemical analysis; accumulates all the errors that exist in proximate analysis (CP,CF, EE, ash)

%NFE =

%DM - (%EE + %CP + %ash + %CF)

Advantages of TDN

used for a long time and many people are acquainted with it

Disadvantages of TDN

-is a misnomer (not an actual total of the digestible nutrients in feed)
-does not include digestible mineral matter
-digestible fat is multiplied by 2.25; feeds high in fat could have TDN values greater than 100%
-based on chemical determination and not related to actual metabolism of animal
-expressed as a % or in weight, whereas energy is expressed in calories
-considers only digestive losses; does not take into account losses in urine, gases and increased heat production
-over evaluates roughages in relation to concentrates due to heat loss in high fiber feed

Starch Equivalent (SE)

expressed energy value of feeds relative to the net energy value of the common feed constituent, starch

Example of SE calculation

Energy of corn = 3.52 Mcal/kg
Energy of starch = 4 Mcal/kg
3.52/4 = 0.88 SE

Calorie

unit of heat used to describe energy yielding capability of foods (and fuels) on complete combustion; the amount of heat required to raise 1 g of pure water from 14.5 C to 15.5 C