lecture quiz 12: biological evaluation Flashcards
feed to gain ratio
- aka feed conversion ratio (FCR)
- FCR = (feed consumption)/(body weight gain)
- lower # is better ➔ produce more with less feed
- for every pound of weight gain/milk/eggs prod animal consumed x pounds of food
- well balanced diet imrpoves FCR
- industries selected chx w/ lower FCR
- FCR measures feed efficiency for meat animals
- higher for ruminants than chx/pigs b/c fed lower quality diet
- can only compare using human-edible food
digestibility
proportion of feed that is not excreted & assumed to be absorbed by amimal (%)
- looking for ways to improve digestibility of feedstuffs (e.g. processing/grinding)
- can be calculated for DM, organic matter, & various nutrients (& energy)
apparent digestibility
= (amount consumed − amount feces)/amount consumed x 100
- assumes all DM in feces is from undigested feed
- there are substances in feces not arising directly from feed = metabolic fecal products (MFP)
- intestinal cells & mucosa
- enzymes secreted in GI
- microbial mass
- MFP mainly important for proteins, but have lipids (e.g. cell membranes)
- underestimates digestibility (always lower than true digestibility)
true digestibility
= [amount consumed − (amount feces − MFP)]/amount consumed
- accounts for metabolic fecal products
- MFP can be quantified by measuring fecal output of fasted animals (only for non-ruminants)
- always higher than apparent digestibility
- for fiber: apparent always = true (animals cannot make)
feed energy evaluation systems
- gross energy has little direct value ∴ energy systems evaluate “available” energy content
- 2 energy systems:
- total digestible nutrients (TDN)
- caloric system
caloric system
- uses gross energy as a start to get energy values of feedstuffs using bomb calorimetry
- helps convert gross energy system to usable energy values to formulate diet
- accounts for energy losses
- if you don’t meet energy requirement animal loses weight
- surplus energy ➔ weight gain
- digestible energy (DE)
- metabolizable energy (ME)
- net energy (NE)
- maintenance energy (NEm)
- productive or recovery energy (NEp)
digestible energy
DE = GE − FE
- FE = fecal energy
- accounts for energy lost in feces
- represents energy absorbed by animal but not necessarily available for usage
- some energy lost along metabolic processes
- burn feces in bomb calorimeter
metabolizable energy
ME = DE − UE (− MtE)
- UE = energy lost in urine
- bomb calorimetry (must be freeze-dried first)
- MtE = energy lost in gases
- account for in ruminants (non-ruminants also have but negligible)
- anything you can burn has energy
- don’t account for CO2 b/c non-combustible
- measure methane production in respiration chamber
- apply heat of combustion (~212.5 kcal/mol)
- represents portion of ingested gross energy left over after accounting for losses in feces, urine, & methane gas
- still does not represent total energy available
- used for energy evaluation of horses
- ME available for most species
main indicator of whether or not you’re meeting energy requirements is…
body weight gain or body weight loss
net energy (NE)
NE = = GE - UE - MtE - HI
- accounts for heat loss via heat increment (HI)
- most accurate energy value you can get
- portion of GE in diet that animal can readily use for maintenance, growth, lactation, & production
- not available for all feeds & species
- used for beef cattle & dairy cows ➔ more energy losses for ruminants
heat increment (HI)
- heat of nutrient metabolism
- heat of fermentation (from the rumen, cecum, & colon)
- useful in winter for animals raised in a non-confinement system
- could be harmful in summer under hot envir conditions
- dietary protein > dietary carbs > dietary fats
- forages > grains
- dietitians can alter diet to modify HI depending on envir conditions
- hard to measure
- estimate values using equations
- bottom-up approach = adding maintenance energy + productive energy
bottom up approach to net energy
NE = heat energy (from maintenance) + NEp (productive energy retained in tissues, milk, conceptus, etc.)
- whenever energy is used for maintenance there is heat generated
- no heat associated w/ production/weight gain
- heat energy (HE) can be directly measured by isothermal calorimetry
- during fasting: ant heat generated must be from maintenance
- during fasting: HI = 0
maintenance energy (NEm)
energy required for:
- basal metabolism
- voluntary activity
- thermal regulation
productive or recovered energy (NEp)
energy used for:
- gain / growth (muscle, fat)
- lactation
- egg production
- conceptus
energy values
- DE, ME, NE
- species-dependent
- too laborious to measure routinely
- estimations come from chemical composition