Net Energy

energy

is defined as the capacity to do work. In animal nutrition,

energy is not a nutrient itself but is contained within the chemical

bonds of nutrients like fats, carbohydrates, and proteins.

Interconversion

cells convert chemical energy from feed into mechanical, electrical, or heat energy

maintenance

more than 50% of feed energy is typically used for basal metabolism

The biological flame

early researchers like Lavoisier equated animal metabolism to a flame as both consumer oxygen and produce heat

first law of thermodynamics

energy can neither be created or destroyed

second law of thermodynamics

entropy always increases
no energy transformation is 100% efficient

heat production types

direct/indirect calorimetry

direct calorimetry

measures heat production directly

indirect calorimetry

estimates heat produced indirectly from oxygen consumption, carbon dioxide production, and ratio of CO2 to O2

who pioneered direct calorimetry?

Lavoisier for measuring BMR

energy

The capacity to do work.

▪ Feed provides chemical energy.

▪ Cells convert chemical energy into

mechanical, electrical or heat energy.

▪ >50% of feed energy used for BM.

gross energy

the total energy released as heat when a substrate is fully oxidized, often measured in a bomb calorimeter

carb/starch yield

4-4.1 kcal/g

protein yield

5.4 kcal/g (4 kcal in biological system)

fat yield

9-9.4 kcal/g

GE formula

GE (kcal/kg)=(% Fat×9.4)+(% Starch×4.1)+(% Protein×5.4)

bioenergetic

heat increment

none of the processes run at 100%
heat lost at every step
HI is energy given off as heat during digestion and metabolism above maintenance
represents the inefficiency of energy use
AKA specific dynamic action/dietary thermogenesis

what are the sources for HI?

digestion, fermentation, waste product formation, nutrient metabolism

Variability: HI is the "tax" on energy use and varies

significantly across different species and feed types.

how is heat produced?

basal metabolism, GI microbes, HI of feeding
body size/surface area - different tissues have different metabolic rate

summary

• Energy is an important concept.

• Energy itself is not a nutrient but is contained within

nutrients.

• Energy is conserved, neither created nor destroyed

but interconverted from one form to another (chemical

to biological).

• Animals utilize different nutrients as energy sources.

• Measuring heat is necessary to determine NE.

• HI varies across species.

• Improving efficiency of dietary energy use is essential

to reduce costs of animal production and minimize

nutrient waste.

why is improving efficiency of dietary energy important?

reducing animal production costs and minimizing environmental waste.

conservation

Energy is interconverted from

chemical to biological forms but is never lost from

the total system.

precision feeding

By understanding NE values,

nutritionists can formulate diets that more

accurately meet the animal's status.