1.4 Comparative Nutrition - Nutrient Metabolism

Question 1

What is the vast majority of AA requirements for?

Answer 1

Protein synthesis
- Maintenance: protein turnover, tissue repair
- Growth: tissue synthesis
- Production: eggs, feathers, pregnancy, etc.

*Balance btw protein synthesis and protein degradation; always a req for AA, even at maintenance

Question 2

What are AA requirements driven by (factorial approach)?

Answer 2

1. Amount for fxnl purposes
2. Rate of endogenous losses
3. Rate of loss to oxidation or other metabolic pathways

Requirements = sum of the above processes

Question 3

What is ‘ideal protein’?

Answer 3

Refers to the AA balance in the complete diet, not necessarily an “ideal protein source” that can be added as a single ingredient to the diet
- supply of aa as needed by animal; no deficiency, no excess

Question 4

Why are all other essential AA expressed as a percentage of lysine?

Answer 4

1. usually first (pigs) or second (chickens) limiting AA in practical diets
2. role of lysine is essentially just protein synthesis
3. few metabolic interactions
4. analysis of lysine

Question 5

What does ideal AA balance depend on?

Answer 5

Depends on type of need
- Maintenance vs Growth, Milk, Eggs (similar in AA profile)

Question 6

Why would growth, milk and eggs require a similar AA profile?

Answer 6

All are used for growth!

Question 7

Why do the units for maintenance vs growth differ for AA?

Answer 7

Maintenance: mg/kg^0.75
- expressed based on metabolic body wt bc as animals get bigger, their req don’t scale up proportionally to absolute BW

Growth: g/100g
- for every 100g of body growth, xg of xAA is required

Question 8

What does ideal protein change with (aka differing AA pattern)?

Answer 8

Type and level of performance
- growth, milk, eggs

In the context of:
- relation of maintenance to level of performance

Question 9

Do we worry about over-supply of specific essential AAs in practical diets?

Answer 9

Generally, no
- rare to see excesses that would have a physiological effect
- cost of getting the balance “exactly” right
- excess essential AA can supply: amino nitrogen for non-essential AA and carbon skeleton for energy metabolism

Question 10

Pigs and chickens can synthesize non-essential AA. What part can be synthesized, what must be supplied?

Answer 10

• Can synthesize carbon skeleton
• Amino nitrogen must be supplied from pre-existing AA
  *both non-essential and essential AA can provide amino N

Question 11

What are the optimal ratios in feed protein of EAA to NEAA for pigs and broiler chickens?

Answer 11

Pigs: 45% EAA: 55% NEAA
Chickens: 50% EAA: 50% NEAA

Question 12

What happens if non-essential AA are too low or too high?

Answer 12

Too low
- Growth performance suffers
= restricted ability to synthesize other non-essential AA
= breakdown of essential AA to supply amino groups

Too high
- Increased nitrogen excretion
= energetic cost of nitrogen excretion

Question 13

What is meant by ‘complementary value of feedstuffs’?

Answer 13

• Few plant-based proteins supply AA in the ratio needed to synthesize body protein
• Complement: two or more protein sources that supply essential AA in different ratios and together, they come closer to meeting the animal’s requirements
• After complementing, can closer the ‘final gap’ by using synthetic AA

Question 14

Why are synthetic AA added to a diet?

Answer 14

To address specific AA limitations

Question 15

What are 4 effects of including synthetic AA in addition to protein feedstuffs to diet?

Answer 15

1. Less protein feed in diet
2. More cereal grain in diet (cheaper)
3. Reduced dietary protein content
   - reduces N excretion
   - possibly reduces odor emission
4. Most cost-effective (up to a point)

Question 16

Amino acid metabolism overview

Answer 16

1. dietary protein
2. enters the stomach (pigs) or proventriculus/gizzard (chickens)
3. goes to the SI where it is either metabolized or sent to the liver following absorption
4. At the liver:
   - Liver protein synthesis
   - Export to peripheral tissues
   - AA catabolism

Question 17

What is the process of amino group removal called?

Answer 17

Transamination: if amino group is being stuck to a different C skeleton to form a NEAA

Deamination: if amino Nis available in excess and not needed, amino group is converted to ammonia and subsequently uric acid (birds) or urea (mammals)

Question 18

What is the fate of the carbon skeleton following amino acid catabolism?

Answer 18

1. Energy (ATP generation)
   - skeleton is a substrate for gluconeogenesis or ketogenesis
2. Fat synthesis

Question 19

What is the difference btw ketogenic and gluconeogenic AA?

Answer 19

Ketogenic enter the kreb cycle with 2-C; 2-C are always lost with each turn of the cycle as CO2, so there is no net gain of C and glucose.

Gluconeogenic enter with 3-5C, so there is a net gain.

Question 20

What is the fate of nitrogen following amino acid catabolism?

Answer 20

• Amino N can be used for non-essential AA synthesis
• Excess N is excreted
  = urotelism (mammals): less energy to produce, more water needed
  = uricotelism (birds): less water needed, more energy to produce

Question 21

Excess amino N is first converted to…

Answer 21

Ammonia, which is highly toxic
- needs to be excreted immediately (fish), or converted to a less toxic form for temp storage before excretion

Chickens - uric acid
- birds lack a urea cycle
- insoluble in water
- stored in urodeum
- excreted with feces

Pigs - urea
- produced via the urea cycle
- soluble in water
- stored in bladder, excreted in water (urine)

Question 22

Birds lack a urea cycle while mammals do not. What do birds have a greater dietary req for?

Answer 22

Arginine
- for mammals (pigs) it can be produced through the urea cycle

Question 23

Uric acid synthesis is more complicated and more energetically expensive than urea synthesis. What is the benefit to making uric acid for birds?

Answer 23

1) storage of wastes during incubation
- maintenance of osmotic pressure in egg; waste can build up as egg develops

2) reduced water requirement in adult birds
- decreased body wt

Question 24

Because birds produce uric acid, what do they have greater dietary requirements for?

Answer 24

1. Glycine
   - 1 mol consumed for each mol of uric acid
2. Methyl groups from Met
   - contribute to formytetrahydrofolate
3. High protein diets increase requirements for glycine and methionine

Question 25

Over- and underfeeding with AA are avoided by applying what concept?

Answer 25

Ideal Protein

Question 26

What happens to excess AA?

Answer 26

They are catabolized to yield C skeletons and amino nitrogen