Protein Flashcards
Discuss the short comings of using CP to estimate the value of a feed
1.All N in feed is from protein
- not all the N in feed is from protein . Some is from simple nitrogenous compounds
- All feed protein contains 160g N / kg
- Different feed proteins contain different N content
Why is crude protein not a sufficient nutrient term when describing protein for ruminant animals?
-gives indication of N content of feed
- Gives no indication of the value to the animal
True vs Apparent digestibility
TRUE = measures the actual proportion of a nutrient absorbed by the body from the diet, accounting for endogenous losses
APPARENT = measures the proportion of a nutrient absorbed without accounting for endogenous losses.
Explain what Endogenous N is
= Basal N + Specific N
BASAL N
- Unrelated to quality or quantity of dietary protein
- Depends on quantity of DM passing through gut
- constant regardless of diet
SPECIFIC N
- Related to quality and quantity of dietary protein
- also related to fibre , ANF
Sources of endogenous nitrogen
Saliva
-Bile
-Gastric and pancreatic secretions
-Cells sloughed off mucous membrane of gut
Why is it not possible to feed a N free diet to ruminants animals?
- ruminants rely on microbial fermentation in their rumen to digest and utilize feed.
- Microbes in the rumen require nitrogen to function properly.
- Therefore, without nitrogen, the microbial population cannot thrive, hindering the digestive process in ruminants.
What does microbial protein (MCP) synthesis require
Requires N from AA, peptides, ammonia
what does microbial protein contribution to host depends on?
- Speed and extent of microbial breakdown of dietary N fraction.
* Microbes require energy too - Efficiency of transforming degraded material into microbial protein
* How well N can be captured - Digestibility of microbial protein by mammalian enzymes
- Biological value of microbial protein
* What amino acid profile is made available to host?- the biological value reflects how well the amino acid composition of microbial protein meets the nutritional needs of the host animal.
Different systems are available to evaluate feed protein for ruminants. To evaluate feed protein for ruminants consider:
- Degradability of protein in rumen
- In sacco
- Rate of degradation
- Rate of passage - Synthesis of MCP in rumen
- Efficiency of N capture
- Microbial yield
- Balance and synchrony of FME and CP - Digestion in lower gut of feed and microbial protein
- Protozoal vs bacterial protein
- Composition and digestibility of RUP - Efficiency of utilisation of absorbed amino acids
- Composition of bacterial protein
- Any limiting AA’s???
Factors affecting degradability of N
- Innate degradability
- influenced by surface area available for microbial attack and
-Physical and chemical nature of protein - Time spent in rumen
- i.e. Rate of passage
- slower passage rate = increases degradability
How is degradability measured?
- In vivo
- In sacco
- In vitro
How is degradability measured In sacco
- Feed is incubated in synthetic bags suspended in rumen
- After incubation, the bags are removed, and the remaining undegraded protein is measured.
*p = protein disappearance regressed on time
*a = represents rapidly degradable protein
*b = represents slowly degradable protein
*c = rate of disappearance of potentially degradable fraction b
*t = time of exposure
Short comings with In sacco procedure ?
- Soluble protein that would naturally pass through the rumen without being degraded may still degrade when placed in the sacco bags.
- ADIN, which is believed to be undegradable, can actually disappear during incubation
- Microbial protein inside the bags can add to the nitrogen content measured.
Rate of passage is faster for:
- Smaller particles
- Particles of higher density
- More highly hydrated particles
- More highly digested particles
rate of passage increases with increased DMI.What factors affect rate of passage
- During advancing pregnancy, the rumen’s capacity is limited due to the growing fetus, which increases the rate of passage.
- Lactation typically increases both DMI and the rate of passage as the animal needs more nutrients to produce milk.
- If an animal has excessive body condition, it might reduce its DMI and subsequently slow down the rate of passage.
- High temperatures can decrease both DMI and the rate of passage as animals tend to eat less during hot weather, slowing down the movement of feed through the digestive system.
