4.1 - Energy

energy

• animals can get energy from their diet → carbs, fats, & proteins

• nutritionists formulate diets so that carbs provide energy (fats & proteins are costly)

• what an animal eats is not what it gets (in terms of energy)

cell diagram

• food enters

  • through catabolic pathways, it is broken down to building blocks

• in order for building blocks to be converted to macromolecule needed by cells (anabolism), cells must use even more energy

• catabolism & anabolism use energy & produce heat → represents energy loss

dietary energy

• energy required in the highest amounts is in an animals diet

• feeding standards for formulating rations for all species are based on some measure of energy with additional requirements for proteins, amino acids, EFAs, vitamins, & minerals

• animals derive their energy from dietary organic compounds found in their diet

  • organic components are digested, absorbed, & subsequently oxidized (burned up) in the animals cells

• carbs are used to provide the bulk of energy that an animal requires because of their relatively low cost per unit of energy

energy

the amount of heat produced when a compound is completely oxidized (burned) in the body

• loss of energy from the body

units used to measure energy

calories; British thermal units (BTUs); Joules

• US: calorie, kcal, mega calorie

• European countries: Joule

calorie (c)

amount of heat required to increase the temperature of 1 gram (g) of water 1 degree C (4.1855 joules)

calorie (C)

also a kilocalorie which equals 1,000 calories

mega calories

equals 1,000 kcal = 1,000,000 cal

gross energy (GE)

amount of heat produced when a feed is completely oxidized (burned)

• determined within a lab using bomb calorimeter

GE is the energy available in feed before animal eats it → is much more than the amount the animal actually gets

digestible energy (DE)

measure of the amount of energy apparently absorbed from a feed after it has been consumed & digested

• less than gross energy → process of digestion consumes energy

metabolizable energy (ME)

determined by subtracting energy losses in urine & combustible gases from the digestible energy (DE) value

• slightly more accurate than DE as an estimate of the amount of energy available for animal use

• much more difficult & expensive to determine

  • usually only seen for avians & sometimes swine

*urine & combustible gases are products of digestion → can account for up to 10% of gross energy in ruminants

net energy (NE)

determined by subtracting energy losses resulting from rumen fermentation & tissue metabolism from ME

• accounts for every loss though metabolism

  • most accurately predicts the amount of energy thats going to be available for use by the animal for maintenance & production

total digestible nutrients (TDN)

method to estimate energy content of feed

dietary energy diagram

gross energy* → digestible energy** → metabolizable energy*** → net energy → maintenance & productivity

*fecal energy loss

**gaseous energy loss

***heat increment

digestibility

the difference between what goes in & what comes out → WHAT THE ANIMAL ACTUALLY USES

• animal eats feed → feed goes through GIT (is digested & absorbed) → what is leftover comes out

• energy digestibility = measuring energy value of feed & energy value of poop

• need to think about what affects digestibility & what’s used/lost in between

in the process of digesting & metabolizing energy:

the greatest loss is in the feces → dietary components the animal is unable to digest

• diet components influence amount of feces produced

• level of feed consumption enhances digestibility

• diarrhea, presence of toxins, & parasite infections often reduce digestibility

  • proper feeding & feed processing can enhance digestibility

what determines the amount of feces produced

diet → more undigestible components = more feces

digestibility of diets for different species

• monogastrics digest more digestible than herbivores diets

• young animals (particularly mammals) are fed diets that are much more digestible compared to adult diets

• high quality diets fed to poultry & swine → may be digested to the extent of 85% or more

• poor quality diets such as straw, often fed to ruminants → may be less than 35% digestible

level of feed consumption & digestibility

in ruminants digestibility decreases as the level of feed intake increases → due to increased passage rate

• more feed = passing through GIT faster → microbes have less time to work on feed

losses from metabolism

• heat produced as a result of microbial fermentation in GIT (heat of fermentation/fermentation heat)

  • heat can be used to maintain body temp

  • if excess heat is produced, it must be dissipated & lost

• heat produced when nutrients are oxidized → referred to as heat increment

  • 1st largest heat increment is associated with metabolism of proteins (amino acids), 2nd largest from metabolism of carb, 3rd largest from metabolism of fats

• this heat can also be used to warm body in cold environments

  *both heat of fermentation & heat increments can be detrimental if animal is in heat stress situation

metabolism as an “industrial plat”

• part of metabolism is making/manufacturing new things

• in industrial plant, lots of machinery manufactures new things → machinery produces heat

• heat increment + heat of fermentation can be used to warm an animals body

  • ex. horses left out on pasture in winter during unexpected snow storm

    • 1st instinct may be to feed high quality, digestible feed

    • heat increment in cold stressed animal can be used to warm them up

    • feeding medium, lower-quality hay will cause the organisms in cecum to work hard to digest feed, producing lots of heat

energy requirements affected by:

• age

• species

• activity level

• production level

• environmental conditions

• nutrient deficiencies

energy requirements are directly related to body surface area

• heat is either lost or gained in proportion to the bodies surface area exposed to the environment

• multiplying the body weight by 0.75 provides a good estimate of of body surface area → metabolic body weight

  • can be used to estimate the energy requirements of species whose body weights differ widely (ex. elephant vs hummingbird)

management practice influence on surface area & rate of heat lost

practices can affect heat or cold stress

• shearing sheep increases their susceptibility to cold stress, but reduces heat stress

• winter hair coats provide more insulation, as does a thick layer of body fat under the skin

• in dry areas, sprinkling animals with water during hot periods increases evaporation through heat removal in the body & reduces heat stress

• cools with fans

• heating with heat lamps

• providing shelter from sun/wind/rain, etc

energy deficiency

• wild species may go through alternating period of energy surplus, adequacy, & deficiency as seasons change & availability/type of feeds change

• free-ranging domestic animals or animals on native pastures may also experience season fluctuations

  • extremities of deficiencies are usually less sever because livestock owner supplies supplementary feed

• animals reared in confinement should NOT experience energy extremes

• when energy deficiency occurs, animal must get energy from somewhere else

  • 1st goes to body fat reserves & mobilize/burn fat to sustain themselves → results in loss of body fat, weight loss, & emancipation (in severe cases)

• periods of energy deficiency can have a negative effect on an animal

why it matters

• only a fraction of energy found in a diet actually gets to the animal to be used

• nutritionists have to understand where the energy is lost & how to formulate animal diets to account for or minimize losses