11 – Protein Quality Flashcards
What ‘type’ of energy do you want to look at with a high protein diet?
- NE
o Taken away energy from feces, urine + gases and the heat increment
Why is protein inefficient as an energy source?
- Energy cost of
o Protein metabolism
o Nitrogen excretion
o Heat increment
o Conversion of protein to fat - *why high protein diets are poor for finishing animals
What are 2 things that determine the nutritional quality of a protein?
- AA content of the protein relative to the requirement of the animal (does it have the right mix of AA?)
- Digestibility of AAs in protein
Protein digestibility
- Feed proteins are digested in stomach and SI
- Absorption occurs in SI
- NO absorption of AA in LI
What happens to undigested feed protein in the LI?
- Digested by microbes in LI and turned into microbial protein
- *microbial protein is mainly excreted in FECES
Total AA vs digestible AA
- Percent AA absorbed in gut differs between feed ingredients
- *diet formulations based on total levels of AA are INACCURATE
Absorption vs. digestibility
- Absorption: amount of dietary component passing across the gut=hard to measure
- Digestibility: amount of dietary component removed from digesta=easier to measure
- *assumed that AA that are digested are absorbed, BUT NOT always true
What is apparent fecal digestibility?
- AA found in feces subtracted from AA in feed
- Ex. 10g lysine ingested, 2g lysine in feces=8g absorbed=apparent fecal digestibility=80%
- **inaccurate
Microbial metabolism of AA
- Microbes in ceca and LI may change AA by deamination and transamination
- *apparent fecal digestibility coefficients may be inaccurate!
What is the equation for true digestibility?
- 100% x (AA ingested – (AA in feces + AA metabolized)) DIVIDED by AA ingested
- *AA ‘lost’=positive value (decreased amount in feces), AA ‘lost’=could be negative(if it is being created)
What can be done to ‘bypass’ the microbes and calculate a digestibility coefficient?
- Capture digestive fluids at the distal ileum (less bacteria in SI)
- *Digestibility coefficients calculated based on appearance in AA prior to distal ileum
o Use ileal cannulation
What is the equation for the apparent ileal digestibility coefficient (AID)?
- AID = (AA intake – AA ileum) divided by AA intake
- *effect of microflora on AA is smaller
- **still not taking into account endogenous contributions
Endogenous contributions
- AA are constantly lost from digestive enzymes, enterocytes, bile, mucus and other sources
o These AA are secreted into lumen of SI
o Some are NOT reabsorbed and end up in digesta captured at the distal ileum - **if take into account=gives us TRUE ileal digestibility
What is the equation for the true ileal digestibility coefficient?
- TID = (AA intake – (AA ileum -AA endogenous)) divided by AA intake
How can you measure endogenous losses in a pig?
- Capture the digestive fluids at distal ileum AFTER a nitrogen FREE diet has been feed
AA requirements of monogastrics
- Animals require AA NOT protein
o AA=building blocks for protein - Lean meat mainly consist of H2O and protein
o *we want as much lean meat deposited as possible - *protein synthesis is an ‘all or nothing’ event
o All AA need to be available at the same time
What do AA requirements depend on?
- Species
- Age
- Production level
What determines an animal’s capacity for lean meat deposition?
- Genetics
- *different genetics have different requirements for AAs
What determines if the genetic capacity is utilized?
- Nutrition
