1st Law of Thermodynamics = energy is not created nor destroyed Þ can be accounted for somewhere in the animals body.

Unavailable = (FE = fecal energy; UE = urinary energy; CH4)

Useful = work

Heat = Heat increment

Digestible energy = gross energy - FE

Metabolizable Energy = GE-FE-UE (-GPD = CH4)

Actual energy available to tissues for metabolism

Net Energy = GE - FE - UE (-GPD = CH4) - HI

Actual energy used for work

NEM = maintenance

NEP = Production (growth, lactation, work (race, run, etc.), fiber production (wool, mohair, etc.), egg, fetus, etc.)

 

Energy Utilization:

1. Digestion & Absorption of organic compounds containing covalent bonds

2. Excretion of energy containing compounds in feces & urine. Energy is not available to animal tissues

3. Metabolism of compounds that breaks the covalent bonds, transfers electrons and releases energy

4. Trapping of energy as ATP ® work

5. Produce heat ® inefficient meatbolism

 

Food Energy: All energy we get is from food

Oxidation of food releases free energy from chemical bonds

Oxidized to CO2 + H2O via enzymes

Oxidation: loss of electrons from a compound (ie hydrogen).

A compound is oxidized if reaction leads to an increase in O2 content and decrease in H content

Reduction: Gain of electrons ( ie hydrogen).

A compound is reduced if the reaction leads to an increase in H content & decrease in O2 content.

Redox State: determines caloric density; more reduced = more caloric dense (more electrons [H] for transfer). Fats = 9, CHO = 4, Protein = 4. Fat is more reduced, not much O2. Oxygen is the terminal electron acceptor in the body - reduced to H2O.

Electron Carriers: transfer electron (H) in redox reactions. Known as coenzymes, serve as electron carriers.

NAD = Niacin, also NADP (phosphate group added)

Oxidized

Reduced

NAD

NADH

NADP

NADPH

FAD = Riboflavin

Oxidized

Reduced

FAD

FADH2

 

When released, electrons used for energy - ATP!! This is done through electron transport.

 

Adenosine Triphosphate

ATP - produced as a result of oxidation, provides energy for muscle (contraction). Each phosphate group has 7.3 kcal:

ATP ® ADP + Pi + 7.3 kcal

ADP ® AMP + Pi + 7.3 kcal

Net reaction = ATP ® AMP + 2Pi + 14.6 kcal

Energy trapped & released

Transfer of energy in the body will be in phosphate bonds.

Creatine phosphate = 10.3 kcal

ATP = 7.3 kcal

Functions:

1. muscle contraction - creatine phosphate + ADP « ATP + creatine

2. synthesis of new compounds - link AA together = protein (4 ATP/link)

3. transmission of nerve impulses

4. active absorption (in SI)

5. heat production - via oxidation of foods (thermoregulation)