Quiz 3

Energy Metabolism- vitamins

what is energy flow

movement and transformation of energy through the animal

what does energy flow require

digestion, absorption, and metabolism

what does energy flow end as

heat, work, storage, product, waste

energy flow: gates and filters

feed energy enters and is partitioned at multiple steps

what does digestion gate

how much becomes digestible energy

what does metabolism gate

NE (net) energy and outputs

what is intake affected by

energy density, environment, and health

intake

determines the total energy available to the system. Regulation differs across species.

digestion

releases absorbable fuels

absorption

moves fuels into blood/lymph

what shapes digestion and absorption

species anatomy shapes the outcome

What do monogastrics rely on for energy

carbs—> glucose (mostly), starch digestion —> glucose absorption. Glucose is a major circulating fuel. Less fermentation before absorption

What do ruminanats rely on for energy

carbs—> VFAs (mostly). Fermentation converts carbs to VFAs. VFAs are absorbed through the rumen wall. Methane represents an energy loss

acetate

major product, fat synthesis substrate

propionate

key gluconeogenic precursor

butyrate

energy for rumen epithelium; contributes to ketones

absorbed fuels: What enters the metabolic pool?

fuels enter pathways to produce ATP

What enters the metabolic pool in monogastrics

glucose, amino acids, fatty acids

What enters the metabolic pool in ruminants

VFAs, amino acids, and limited direct glucose

Glycolysis

A cytosolic pathway that converts glucose to pyruvate. Provides intermediates for synthesis

What is the net yield of glycolysis

2 ATP per glucose (direct)

What is the aerobic fate of pyruvate

It is converted into acetyl-CoA and then goes to the TCA cycle

What is the anaerobic fate of pyruvate

it is converted to lactate

What does the fate of pyruvate depend on

direction depends on oxygen and tissue state

TCA cycle

oxidizes acetyl-CoA to CO2, generates NADH and FADH2, central integration point for carbs, fats, and proteins

oxidative phosphorylation

ETC uses NADH/FADH2, produces most ATP in aerobic respiration, and inefficiency produces heat

ATP yield summary

Approx total = 30 ATP per glucose (aerobic), NADH=2.5 ATP, FADH2= 1.5 ATP, yield depends on shuttle systems and tissue

fat metabolism

long-term storage

protein as energy

Amino acids can be oxidized if energy is low, requiring deamination; nitrogen is excreted, less efficient than carbs/fats for energy

gluconeogenesis

Glucose is still required for the brain, RBC, and lactose; ruminants synthesize glucose largely from propionate. Glucose supply is linked to ketosis risk

Why is glycogen used as energy storage

quick-access, limited storage

why is fat used as energy storage

large capacity, energy-dense storage

why are both glycogen and fat used together as energy storage

mobilization differs by hormonal state (ex. cortisol, insulin, etc.)

heat production: Where the lost energy goes

heat from basal metabolism + activity + processing, , influenced by diet composition

what can lost energy/ heat be measured by

can be measured by calorimetry

methane: ruminant-specific energy leak

Fermentation produces methane as a byproduct, representing energy loss from the diet, target for mitigation strategies

The role of fiber (NDF) in energy flow

NDF influences rumen fill and intake; higher fiber often lowers energy density, and digestibility shapes DE/ME outcomes

proximate analysis

crude fiber is limited

detergent system

NDF/ADF better predicts digestion

feed analysis: Why we measure fiber differently now

used to estimate energy supply potential

efficiency “k” factors

efficiency varies by maintenance, growth, lactation, and fat gain. It depends on substrate and function; NE systems improve precision

measureing digestiblity

apparent vs. true digestibility concepts, ileal vs fecal measures (monogastrics), trials, indicators, and lab-based prediction

intake prediction (why it’s hard)

intake is dynamic, not fixed, influenced by environment and diet structure, systems use equations/models to predict

energy flow overall process

intake sets the ceiling, digestion determines what’s absorbed, metabolism partitions to ATP/ heat/ storage/ product

from fuels to outcomes

Different fuels follow different metabolic paths; all fuels ultimately support ATP, storage, product formation, or loss (heat/CO2). Fuel fate explains performance and efficiency

fuel priorities and metabolic flexibility

fed vs fasted states change fuel choice, lactation shifts priorities, stress and disease re-route energy

where energy disorders begin

when demand outpaces supply, when fermentation becomes unstable, when transition diets are poorly managed

Feeding systems: What are we trying to control

Match energy supply to energy demand. Stabilize intake and rumen/intestinal environment, optimize efficiency, and minimize disease risk

forage-based systems

High fiber intake is limited by fill and digestibility. Lower energy density than concentrate diets. Requires strategic supplementation

What animals are forage-based systems usually used for

ruminants and horses

concentrate-based systems

high energy density; supports high production. Higher risk of rumen instability (rapid fermentation) requires fiber management and gradual transitions

What animals are concentrate-based systems usually used for

pigs, poultry, companion animals

mixed systems and TMR concepts

blend forages + concentrates for consistency. Manage fiber effective length + energy density. Reduce sorting and stabilize intake

ruminant feeding systems

balance fermentable carbs and effective fiber, track ME/NE supply for milk/gain, manage transition periods aggressively

pig feeding systems

ME is commonly used for formulation, high-precision diets to match growth stages, and monitor the energy-to-protein ratio for lean gain

poultry feeding systems

ME-based formulation is common, energy density influences intake strongly, balance amino acids with energy supply

horse feeding systems

Hindgut fermentation supports fiber use, rapid starch loads increase colic/laminitis risk, consistency and forage-first management

Energy evaluation in practice

GE/DE/ME/NE guide diet comparisons, standards differ by species and region, use the appropriate system for the animal and the goal

Energy: protein balance (why it matters)

energy shortfall> protein used for fuel, energy excess with AA shortfall> fat gain, balanced diets improve feed efficiency

Transition periods: the highest-risk windows

diet changes + physiology change= risk, intake often lags behind demand, management focus: gradual change and monitoring

When demand is greater than intake: what happens first

decreased intake and increased demand > negative energy balance > fat mobilization (NEFA) > ketones/ liver load

Negative Energy Balance (NEB)

Demand exceeds intake energy supply, body mobilizes fat> NEFA rise, ketone production may rise (risk)

ketosis

common in high-demand states (e.g. early lactation), increased fat mobilization> ketone bodies, signs: reduced appetite, production drop, lethargy

fatty liver (energy overflow into the liver)

excess fat mobilization> liver fat accumulation, reduces liver function and metabolic capacity, often linked with ketosis and NEB

pregnancy toxemia (small ruminants)

late gestation energy deficit (especially multiples), reduced intake + high fetal demand, ketones rise: weakness and neurologic signs

ruminal acidosis (energy and fermentation disorder)

Rapidly fermentable carbohydrates increase acid load, rumen pH drops: microbial shifts, consequences: reduced intake, inflammation, lameness risk

laminitis (link to energy and fermentation)

Often associated with dietary starch overload and acidosis, systemic inflammation affects hoof tissues, and prevention relies on diet structure and consistency

Bloat (Fermentation and gas handling)

Gas production + impaired eructation can be linked with diet type and fermentation patterns. Prevention: management and diet structure

preventing energy disorders

maintain consistent intake, avoid rapid diet changes, and balance fiber and fermentable carbohydrate

monitoring energy status

body condition score trends, intake behavior and refusals, production patterns (milk yield, growth rate)

fiber strategy: NDF and effective fiber

NDF supports rumen function and intake control, too low> acidosis risk, too high/poor digestibility> energy shortfall