Nutrition Test 2

Water - Ruminant Nutrition 3

First Law of Thermodynamics

Energy is conserved.

• Feed energy is transformed, not created or destroyed.

Second Law of Thermodynamics

Efficency has limits

• Eachenergy transfer increases entropy (disorder), so more energy leaves as heat

• Not all feed energy convered into growth or useful work

Energy balance

Intake energy must equal energy lost + energy retained in tissues

Early calorimetry experiments

Animal heat measured in ice-melting chamber. Linked heat production to respiration by tracking carbon dioxide

Metabolism acts like combustion.

Animals and fire release similar heat for the same CO2 produced, suggesting they “burn” food using oxygen.

Why does measuring heat matter?

Heat is a practical way to quantify energy in nutritional studies.

Where does ATP come from?

Carbs and fats

How do carbs make ATP?

Glucose is broken down by glycolysis to capture usable energy

How do fats make atp?

Fatty acids are split by beta-oxidation to release energy-rich units

Where do carbs and fats synthesized for ATP finish?

Both routes supply the TCA cycle and drive oxidative phosphorylation

Where does the TCA cycle happenn?

In the mitochondria of cells

What starts the TCA cycle?

Acetyl-CoA joining the cycle pathway

Where does acetyl-CoA come from??

Can be made from pyruvate, rumen acetate, or fatty acid breakdown.

Why is the TCA cycle able to loop?

The TCA cycle produces two molecules of CO₂ and regenerates oxaloacetate to restart the cycle.

Outputs of TCA cycle

• 3 NADH

• 1 FADH2

• 1 GTP

What moves to the ETC?

NADH and FADH2

What does GTP become after the TCA?

Quickly converted to ATP to power cell tasks

Where do NADH and FADH2 go?

To the ETC to hand off electrons

• Oxygen acts as the final electron acceptor

What builds a proton gradient?

Electron movement releases energy that pumps hydrogen across the membrane which creates an electrochemical gradient (think: like a battery)

What does ATP synthase do?

Uses the proton gradient to drip ADP and P_i (inorganic phosphate) to create ATP

Why do we track energy at all?

• To account for where feed energy goes when transformed

• Each step subtracts losses before energy becomes useful for work

Net energy “pipeline”

Gross energy → Digestible energy → Metabolizable energy → Net energy

What tracking feed energy helps with?

Comparing feeds by usable energy and not just total energy content

• Link energy to animal outcomes (ex. maintenance or growth)

Energy units

Calories or Joules

1000 calories

Kilocalorie or 1 Kcal

1000 Kcal

Megacalorie or 1 Mcal

1 calorie

4.184 joules (J)

1 MJ

0.239 Mcal

1 Mcal

4.184 MJ

Calorie (cal)

Energy needed to raise 1g of water by 1°C (specifically from 14.5°C to 15.5°C).

Joule (J)

Work done by 1 Newton of force moving 1 meter (equals 1/3600th of a watt-hour).

Net energy best reflects

What supports maintenance and production

Energy is ___ lost as ____ and wastes before use

progressively, heat

Gross energy (GE)

Amount of heat produced when a feed is completely oxidized (burnt)

Digestible Energy (DE)

Measure of the amount of energy apparently absorbed from a feed after it has been consumed and digested.

Metabolizable Energy (ME)

Determined by subtracting energy losses in urine and combustible gases from the DE values

Net energy (NE)

Determined by subtracting energy losses resulting from rumen fermentation and tissue metabolism (from ME)

Total Digestible Nutrients (TDN)

Method to estimate energy content of a feed)

How is gross energy measured?

Heat produced upon complete oxidation of a feed to CO₂ and H₂O in a bomb calorimeter

Bomb calorimeter

Burns a feed sample in oxygen-rich conditions, the temperature rise in surrounding water is converted to energy

Why is GE not “usable energy?”

GE ignores digestion, metabolism, and heat loss processes inside the animal. It is a representation of the feed’s maximum chemical energy content, not the animal’s energy supply.

Energy value depends on

what is digested and absorbed, not burned

Fecal energy

Feed energy that never crossed the gut wall. Higher loss signals poorer digestion and absorption overall

Diet quality changes DE

Highly digestible feed lose less energy in feces

Fibrous feeds can lose

25-40% of gross energy as fecal energy

Fecal energy includes

Undigested feed + microbial cells and products. Gut secretions and sloughed (shed) intestinal cells add measurable energy too.

Unine as a minor loss

Urinary energy is typically small, about 3% of feed energy

Gas loss depends on

Fermentation

Methane

Methane and other combustible gases carry energy out (mainly in herbivores)

If there is low fermentation

ME is about the same as DE

How big is loss from methane?

About 6-8% of intake energy

How do we measure gas energy loss?

Using a respiration chamber to capture and analyze expired gases. Calculate energy from combustible gases, mainly methane in ruminants.

What would cause an increase in methane output?

Higher-fiber, more fermentable diets

Clinical takeaway from methane

For ruminants, methane is an energy penalty (loss of food energy) and a fermentation indicator

How to measure urine energy (UE)

(During digestion trials) Daily urine volume determined and gross energy content of urine samples measured

How to measure methane energy

Indirect respiration calorimetry is used to measure CH₄ gas produced

• ME = Feed DE - (UE + CH₄ energy losses)

Biggest subtraction from energy is

Heat released while processing and using feed

What does net energy support?

Maintenance needs like temperature control and tissue repair. It also powers production: growth, lactation, wool, and useful work.

NEm

NE used to maintain body tissue

NEg

NE used to deposit lean and adipose tissue

NEl

NE used to produce milk

NEp

NE used for fetal growth and development

Fermentation heat

5-10% of gross energy

Microbial fermentation produces

Heat in the rumen and large intestine

Processing feed releases

Heat during digestion, absorption, and nutrient transport, which lowers what remains to support maintenance and production

Fasting heat production (FHP)

Animal’s basal metabolism, reflects tissue catabolism supporting vital functions and thermoregulation

Basal metabolism

Minimum amount of heat to sustain life

How is Basal metabolism measured?

Respiration chamber after fasting and minimal activity. When using thermoneutral conditions, ruminants require longer fasting than nonruminants.

why does FHP matter?

It estimates maintenance energy used in ration formulation and provides a baseline to compare animals and diets consistently

How to measure net energy?

• Indirectly through respiration calorimetry (Heat Production/ HP)

Why is it important to know that heat does not scale linearly?

Because small animals produce far more heart per kilogram than large ones

Why do small animals run “hotter”?

Higher surface area to mass drives faster heat loss to the environment, so they need higher metabolic rate per kilogram to stay warm.

Metabolic BW

BW^0.75