8. Protein Flashcards
Protein Requirements
animals need amino acids
protein synthesis in tissues
essential for life:cell turnover, blood cells, enzymes, hormones
growth and production: skeletal muscle, foetal development, milk production
Protein nutrition in monogastric animals
protein sources differ in their digestibilty and in the proportion of amino acids absorbed and used in body tissues
quality of protein sources assessed by:
biological value: food N - (faecal N+urinary N)/food N - faecal N
It measures the proportion of digested N that is used for protein synthesis in body tissue
It is high when amino acid composition of the tissues being synthesized is similar to that of feed
NPU
protein digestibility also an important characteristic of protein quality
Net Protein Utilisation, NPU
combines digestibility with biological value
NPU = Biological value x Protein digestibility
digestibility and amino acid profile are the most important characteristics of protein quality for monogastric animals
Protein nutrition in monogastric animals
ideal amino acid profile: amino acid composition of feed matches the amino acids needed for tissue protein production
essential amino acid index: sum of proportion of each essential amino acid for a reference tissue that is provided by each essential amino acid in the feed
Protein and Diet formulation
diets formulated on the basis of CP and the essential amino acids likely to be limiting in typical diets
Pigs: CP, lysine, methionine, cystine and threonine
Horses; CP and lysine
cats, dogs, poultry: CP and many essential amino acids
growing animals require more protein
older animals need less protein
Protein in ruminant nutrition
fermentation in rumen
protein hydrolysis, peptide degredation, amino acid degredation = ammonia
main rumen bacteria: bacteroides amophillus, bacteroides ruminacola
butyrivibrio fibrosolvens
proteolytics 30% of biomass in rumen
loss of valuable feed proteins end up as ammonia in the rumen
Microbial protein
bacteria and protazoa use protein breakdown products to fuel their N requirements for multiplication in the rumen
some bacteria use ammonia, others only need aa
for bacterial replication you need a supply of energy
insufficcient energy supply: valuable feed protein lost as ammonia!!!!
the new bacteria and protozoa breakdown products used to form non essential and essential amino acids which are digested and absorbed
Amino acid supply from microbial protein
Microbial protein digestibility
bacteria, 75%
protozoa, 90%
commonly total biomass assumed to be 75-80% truly digestible
microbial cell walls not very digestible
Microbial protein amino acid concentration
can vary with diet
assumes constant at 80% or close to it
nucleic acids have N but no aa!!!!!
Total amino acid supply
not all feed protein degraded in rumen
rumen undegradable or by-pass protein
important component of amino acid supply
digestibility of by-pass protein variable
amino acid composition extremely variable
high quality protein sources may be protected from rumen digestion
Total amino acid supply
absorbed amino acids from microbial protein and absorbed amino acids from rumen undegradable protein
absorbed amino acids not used with 100% efficiency
not enough energy supplied by diet
not correct ratios of amino acids supplied
animal over-supplied with protein
milk production in cattle absorbed amino acids retained in milk with 64% efficacy
beef: 68% young animals, 40% older animals of amino acids retained in body tissue
PDI protein system
Feed component
protein value of ruminant diets; PDI
microbial amino acids absorbed from small intestine
amino acids supplied by undegradable dietary protein and absorbed from the small intestine
Animal component
animal requirement for amino acids
maintenance requirement
production
PDI
the protein value of a feed or diet is their PDI content
PDI: g of true protein truly digestible in small intestine
it is made up of two protein fractions: PDIM, PDIA
PDIA: g of dietary true protein undegradable in rumen but truly digestible in small intestine
PDIM: g of microbial true protein that is truly digestible in the small intestine
rumen degradable feed protein
rumen available energy
each feed has two PDIM vales:
PDIMN and PDIME
PDIM, PDIME
PDIMN: g of microbial true protein that can be synthesized in the rumen from rumen available N
depends on rumen degradability of feed protein
most foraged 70-90%, concentrates variable 30-85%
PDIME: g of microbial true protein that can be synthesized in the rumen from rumen available energy
depends on supply of FOM
assumed 145g microbial protein/kg of FOM
FOM = digestible organic matter - (ether extract - undegradable protein - fermentation products in ensiled feeds)
PDI system: feed component
each feed has a potential and actual PDIM value
the higher of PDIMN, PDIME is the potential value
the lower of PDIMN, PDIME is the actual value
principal determinants of how much microbial protein is produced is rumen degradable nitrogen and rumen available energy supply THEY ARE BOTH NEEDED
calculate how much can be produced with the rumen degradable N supply and the rumen available energy supply
lower of these is the actual amount produced
