Bioenergetics

Question 1

What is biogenergetics?

Answer 1

Energy and its metabolism by animals

It is the study of energy supply, utilization, and loss in animals.

Question 2

What was concluded by Lavoisier and Laplace with their experiment with the guinea pig in ice?

Answer 2

Respiratory exchange is combustion

Question 3

Define energy

Answer 3

Energy is the capacity to do work

Question 4

What types of work are there?

Answer 4

Many kinds: chemical, mechanical, electrical, osmotic, etc.

Question 5

What kinds of energy are there?

Answer 5

Many types: thermal, chemical, electrical, radiant, nuclear, magnetic

Question 6

What type of energy do nutrients contain?

Answer 6

Nutrients contain chemical energy which is yielded upon chemical breakdown and can be used in the body to perform work.

Question 7

How efficient is conversion of chemical energy to work in animals?

Answer 7

It is not 100% efficient.

ATP is the energy intermediate, and the remaining energy is converted to heat (thermal energy)

Question 8

Describe some of the units used to measure energy

Answer 8

The Joule (J) is the international unit. The U.S. uses the calorie (cal) unit.

cal = heat required to increase the temp of one gram of water from 14.5 to 15.5 degrees C

1 cal = 4.184 J

1000 calories (1kcal) = 1 “Calorie”

Calorie, with a capital c, is used in human nutrition

Question 9

What is the first law of thermodynamics?

Answer 9

Energy can neither be created nor destroyed

corollary 1: energy can be inter-converted between different forms

corollary 2: thermal energy (heat) cannot be converted to other forms of energy in the body

Question 10

What is the second law of thermodynamics?

Answer 10

Entropy increases

Energy is lost as heat in metabolic reactions, increasing entropy

Question 11

What is gross energy (GE)?

Answer 11

The total energy content of a given weight of feed, measured as its heat of combustion by bomb calorimetry.

Question 12

Does the GE differ much between feeds like corn grain and straw?

Answer 12

GE is similar between the two. This is why we do not feed animals on a GE basis, however, because corn grain is much more digestible, and the animal is able to take advantage of its energy better.

Question 13

What is digestible energy (DE)?

Answer 13

Digestible energy is energy that was not lost in feces.

DE= GE - FE

Energy in feces must be measured by weighing it and subsampling it. Bomb calorimetry is used on the feces to determine the energy present in it.

Question 14

Does DE vary much between corn grain and straw?

Answer 14

Yes, corn grain is much more digestible than straw.

Question 15

How is DE typically used in nutrition purposes?

Answer 15

It is widely used in non-ruminants.

This is because the non-ruminants have very small methane losses and relatively constant losses in urine and heat increment of feeding. It can be directly measured.

DE has less guessing or mathematical predictions, as digestibility is more consistent in non-ruminants than in ruminants.

DE is not a good measurement for ruminants because it fails to account for methane loss and other metabolic losses they experience.

Question 16

What is TDN?

Answer 16

TDN is total digestible nutrients, and is the unit most commonly used to measure feed energy in the U.S.; it is similar to DE.

TDN = Digested Protein + Digested Carbs + (Digested Fat x 2.25)

TDN can be calculated based on feed analysis and expected digestibility

It has several disadvantages, especially for feeds which vary widely in digestibility, like forages

Question 17

What is the major disadvantage of TDN?

Answer 17

It fails to account for variations in energy losses in urine, methane, and heat, especially in ruminants.

Question 18

What is metabolizable energy (ME)?

Answer 18

This is the energy available for use in tissues, and is the measurement widely used in Europe.

ME = DE - UE - Gas Energy (GPDE)

Ruminants see lower ME values due to higher methane losses while non-ruminants usually have higher ME values.

ME does not account for heat increment.

ME is difficult to directly measure, so it can be predicted from a conversion based on DE or TDN.

ME = (1.01 x DE - 0.45) + 0.0046 x (EE - 3)

Question 19

What animal is ME mandatory for and why?

Answer 19

ME is mandatory for poultry because we cannot get DE from them because their feces and urine (uric acid) is mixed when it exits the vent/cloaca.

Question 20

What are Physiological Fuel Values?

Answer 20

PFVs, aka Atwater Factors, are what’s used in human nutrition in the USA (in food labels)

Developed in the 1900s and still used today because it is simple and closest to the right value. PFVs are based on GE, digestibility in dogs, and correction for urine secretion.

Results are pretty similar to ME, and work well when digestibility is predictable.

Question 21

What is the Atwater Specific Factory System?

Answer 21

A system that accounts for different values of each food, especially differences in amino acids and types of carbs

Question 22

What is the heat increment of feeding?

Answer 22

Heat production resulting from the ingestion, digestion, and metabolism of a given amount of feed (increment above maintenance heat)

Metabolism has a delta G roughly equal to delta H.

Question 23

What is net energy (NE)?

Answer 23

NE is energy that is used to keep the animal alive or the energy retained in the body or by products.

NE= ME- HI
or NE = GE - FE - UE - GPDE - HI

NE is subdivided into NEmaintenance and NEretained

Question 24

What is total heat production?

Answer 24

Total heat production = HI + NEmaintenance

1. Heat increment of feeding results from the ingestion, digestion, and metabolism of feed
2. NEmaint is the heat production resulting from maintenance of basal state

Question 25

What is the gold standard of measuring heat production (HP)?

Answer 25

Direct calorimetry is the gold standard

An animal is placed in an insulated chamber, and the heat they produce is observed as how much it takes to maintain to temperature of the chamber.

Energy from methane loss is also determined

Question 26

What does indirect calorimetry do?

Answer 26

It calculates heat production and is based on the stoichiometry of oxygen used and CO2 and energy produced.

A respiratory quotient is found, and based on the RQ and total oxygen consumption, energy oxidized can be found.

Question 27

How can heat production be calculated using ME and NEr?

Answer 27

HP = ME - NEr

found by rearrangement, see pg 24 of slides

Question 28

How is NEr found?

Answer 28

Weight of products like milk or eggs is acquired, and the energy density is then found with bomb calorimetry.

Question 29

What is comparative slaughter?

Answer 29

This is when one portion of a group is harvested and the carcass energy is determined. Then, a group is fed and their energy in rest is determined.

Question 30

What is NEr?

Answer 30

NEr is the energy of the product or work.

Ex. for a lactating animal, the amount of energy produced by the milk can be found. The NEr is the energy retained in milk.

The energy lost making milk is heat increment. (ex. liver gluconeogenesis or mammary lactose synthesis)

Question 31

What does NE account for? What is it used for?

Answer 31

NE of a feed accounts for all losses.

It is difficult to measure directly.

NE is commonly used for ruminants in the U.S., but is based on predictions of conversion of DE or TDN to NE

The energy values must be separated depending on what the energy is used for; ex. maintenance, lactation, growth (NEm, NEl, NEg)

NEl is usually close to NEm, so the same value is often used.

Question 32

Is HI usually large or small?

Answer 32

HI is normally large (> 30% of ME) and can vary widely.

HI is much larger in ruminant animals.

Question 33

Why are ruminants still raised so often if they are so inefficient with their energy?

Answer 33

Ruminants contribute a higher net protein than any other animals, and are able to take advantage of cheaper food sources that other animals cannot digest. Furthermore, ruminants can be fed byproducts of human food manufacturing.