Introductory Animal Nutrition and Feeding: Digestion, Fiber, Energy, and Water

Comprehensive practice flashcards defining core terms in comparative animal nutrition, digestion physiology, carbohydrate fractionation, bioenergetics, and water balance.

Physically Effective Fiber (peNDF)

• dietary fiber (particle size and density) that stimulates mastication

• maintain the stratified rumen contents

Effective Fiber (eNDF)

• property of a dietary feedstuff to sustain ruminal pH

• chewing activity, and milk fat percentage, quantified as its total capacity to replace roughage in a ration

Mean Fecal Particle Size (MFPS)

• measure of masticatory particle reduction

Optimal Ruminant Dietary NDF

• 25-33% DM, with 70-75% of NDF from forage

Equine Hindgut Acidosis

• reduction in cecal/colonic and fecal pH

• increased gastric ulceration

• from feeding elevated levels of carbohydrates

Autoenzymatic Digestion

• digestion by endogenous enzymes (produced by animal)

Alloenzymatic Digestion

• digestion by exogenous enzymes

• symbiotic relationship, microbes

Sodium-Glucose Linked Transporter 1 (SGLT1)

• secondary active transport symporter located on the brush border membrane of enterocytes

• transports one molecule of glucose or galactose coupled to $2\,\text{Na}^+$ ions into the cell.

GLUT5

• brush border transport protein

• facilitates the passive diffusion of fructose from the intestinal lumen into the enterocyte

GLUT2

• facilitated diffusion transporter situated along the basolateral membrane

• carries glucose, galactose, and fructose into the blood

Mucin Cast

• mucopurulent exudate composed of a mixture of fibrin, mucin, and neutrophils

• sloughed into the stool, triggered in captive giant pandas by high-starch, low-NDF diets

Lactase Deficiency

• lactase activity declines to 10% of neonatal levels after weaning

• causes unabsorbed lactose to exert an osmotic effect and undergo microbial fermentation into hydrogen, methane, carbon dioxide, and short-chain fatty acids

• diarrhea

Proximate Analysis (Weende System)

• analysis scheme that divides feeds into moisture, ether extract, crude protein, crude fiber, and ash

Crude Fiber (CF)

• organic residue left after sequentially boiling a defatted sample in $1.25\%\,\text{H}_2\text{SO}_4$ and $1.25\%\,\text{NaOH}$

• historically underestimates fiber because substantial fractions of hemicellulose and lignin dissolve in the alkali

• BAD MEASUREMENT!!

Nitrogen-Free Extract (NFE)

$$\text{NFE} = 100 - (\%\text{Moisture} + \%\text{Ether Extract} + \%\text{Crude Protein} + \%\text{Crude Fiber} + \%\text{Ash})$$

Neutral Detergent Fiber (NDF)

• insoluble residue remaining after boiling a sample in neutral detergent solution

• hemicellulose, cellulose, and lignin

Acid Detergent Fiber (ADF)

• insoluble residue remaining after boiling in an acid detergent solution

• isolating cellulose and lignin while removing hemicellulose

Total Dietary Fiber (TDF)

• isolates non-starch polysaccharides and lignin into insoluble dietary fiber (IDF) and soluble dietary fiber (SDF)

Amylose

• alpha 1,4 bonds linking glucose subunits

• plant starch polysaccharide

• 20-30% of total plant starch

Amylopectin

• alpha 1,4 and 1,6 bonds linking glucose subunits

• plant starch polysaccharide

• 70-85% of total plant starch

Cellulose

• the most abundant organic compound on earth

• beta 1,4 bonds linking glucose subunits

• resistant to autoenzymatic digestion

Hemicellulose

• beta 1,4 bonds linking glucose, mannose, arabinose, and galactose monomers

• plant cell wall heteropolysaccharide

Lignin

• not a carbohydrate

• increases with plant maturity

• resistant to auto and alloenzymatic digestion

Pectin

• water soluble heteropolysaccharide

• 1,4 linked galacturonic acid “plant glue”

• resists host autoenzymes, but undergoes rapid alloenzymatic fermentation

Inulin

• water-soluble prebiotic homopolysaccharide

• repeating fructose monomers found in plant roots and stems

• selectively promotes beneficial lactobacillus and bifidobacteria in hindgut (probiotic!)

Chitin

• structural polysaccharide composed of $N$-acetylglucosamine monomers found within fungal cell walls

• composes exoskeletons of arthropods and marine invertebrates

Gross Energy (GE)

• total quantity of heat released when an organic substance is completely oxidized to $\text{CO}_2$ and $\text{H}_2\text{O}$ inside an oxygen bomb calorimeter

Digestible Energy (DE)

• portion of gross energy retained after accounting for fecal energy losses

• formula: DE = GE - fecal energy

Metabolizable Energy (ME)

• dietary energy available for tissue metabolism after subtracting urinary and gaseous energy losses from digestible energy

• ME = DE - (urinary energy + gaseous energy)

Net Energy (NE)

• quantity of energy completely useful to the animal for maintenance ($\text{NE}_\text{m}$) and production ($\text{NE}_\text{p}$) after subtracting the heat increment of feeding from metabolizable energy

Heat Increment (HI)

• elevation in heat production following feeding

• heat of nutrient digestion + heat of microbial fermentation

Atwater Physiological Fuel Values

• biological fuel values for human food substrates:

  • 4 kcal for carbs

  • 9 kcal for fats

  • 4 kcal for proteins

  • 7 kcal for alcohol

Basal Metabolic Rate (BMR)

• minimal rate of energy expenditure required to sustain life in an endotherm

Thermoneutral Zone (TNZ)

• ambient temperature range bounded by the lower critical temperature ($\text{T}_\text{LC}$) and upper critical temperature ($\text{T}_\text{UC}$) in which an endotherm maintains normal body core temperature without altering metabolic heat production

Kleiber's Law (Allometric Metabolic Scaling)

• empirical relationship demonstrating that basal metabolic rate scales across species to body weight raised to the $0.75$ power ($\text{BW}^{0.75}$)

• higher mass-specific metabolism in smaller animals

Biological Dose Response

• characteristic response curve illustrating nutrient levels from deficient to abundant

• toxic levels can cause death

total body water

Metabolic Water

• water synthesized during the mitochondrial oxidation of energy substrates

• yields 0.6g from carbs, 1.12 from lipids, and 0.37g from protein

Preformed Water

• the compositional moisture physically contained within ingested food, analytically quantified by measuring weight loss following sample dehydration to constant weight at $105^\circ\text{C}$.

Water Intoxication (Hyponatremia)

• fatal osmotic disturbance caused by excessive water consumption that dilutes extracellular sodium

• draws water into intracellular spaces, causes fatal cerebral edema

Digesta Passage Marker

• inert, unabsorbed, non-toxic, and quantifiable substance added to a diet to track:

  • gut kinetics

  • transit time

  • rate of passage through GI tract

Transit Time ($\text{TT}_1$)

• the elapsed time between consumption of a market and its initial qualitative appearance in the feces

Mean Retention Time ($R_\text{GIT}$)

• the average duration an indigestible marker remains in the GI tract before excretion

  • ex: 4 days in chickens, 17 days in leopard tortoises

Apparent Total Tract Digestibility (aDig)

• the percentage of ingested dry matter or nutrient disappearing during passage through the entire digestive tract: $\frac{\text{Intake} - \text{Fecal Output}}{\text{Intake}} \times 100\%$.

Apparent Ileal Digestibility

• the percentage disappearance of an ingested nutrient prior to the terminal ileum, calculated as: $\frac{\text{Intake} - \text{Ileal Output}}{\text{Intake}} \times 100\%$

• separating autoenzymatic digestion from hindgut microbial fermentation

In Situ Digestibility

• technique that measures the rate and extent of nutrient degradation by incubating feedstuffs inside porous bags suspended directly within the rumen via cannula

In Vitro Digestibility

• two-stage laboratory procedure simulating ruminant digestion

• incubates feed in buffered rumen liquor followed by an acid-pepsin proteolytic extraction to predict in vivo dry matter disappearance