PRINCIPLES OF NUTRITION

Question 1

What is neutral detergent fibre (NDF)?

Answer 1

• Plant cell wall material
• Fibre insoluble in neutral detergent
• Residue containing CW materials = Hemicellulose + Cellulose + Lignin

Question 2

What is acid detergent fibre (ADF)?

Answer 2

• Fibre insoluble in acid detergent
• Residue contains CW material = lignin + cellulose

Question 3

What does NSC stand for?
And what is NSC fraction composed of?

Answer 3

• Non-structural carbohydrates
• NSC fraction composed of Starch + WSC (water-soluble carbohydrates)

Question 4

What is WSC fraction composed of?

Answer 4

Simple sugars + fructan

Question 5

State some factors that affect grass growth/productivity and briefly describe them.

Answer 5

Stage of growth
- Most important factor in nutritional value of grass
- e.g. increased lignin content lowers grass nutritional value

Time of year
- Most rapid in spring & early summer (April - June)

Environment
- Season e.g. reduced growth below 5C
- Climate, topography, soil type
- Light, temperature, rainfall
- Increased productivity in warm & wet conditions

Soil status
- Nitrogen, Phosphorus, Potassium
- Nitrogen fixing plant species
- Soil pH i.e. most grasses thrive on slightly acidic pH

Grass species
- Ryegrass, Timothy, fescue, cocksfoot are high yielding
General management
Cutting & grazing strategies

Question 6

What are the desirable characteristics of low DM silage?

Answer 6

Low pH, low butyrate, low NH3-N, high lactate

Question 7

Why is HT forage high in nutritional value?

Answer 7

Young herbage utilised

Question 8

Rank the starch content of oats, barley and maize from highest to lowest.

Answer 8

Maize, barley, oats

Question 9

What oilseed meal is most commonly used?

Answer 9

Soya bean meal

Question 10

What term is most often used for digestibility?

Answer 10

Apparent digestibility

Question 11

How is in vitro digestibility assessed?

Answer 11

Through work in labs

Question 12

How does increased feeding level in ruminants change ruminal retention time and thus digestibility?

Answer 12

Reduces ruminal retention time and digestibility

Question 13

State the relationship between GE (Gross energy), DE (Apparent digestive energy), ME (Metabolisable energy) and NE (Net energy).

Answer 13

GE (Gross energy) is measured by converting food to heat energy;

GE - Faecal energy = DE
DE - (urine + gaseous energy) = ME
ME - heat increment = NE

Question 14

State the energy system for ruminants, pigs, poultry, dogs & cats, and horses.

Briefly explain why that energy system is used when possible.

Answer 14

Ruminants (ME)
- Use k factor for maintenance, milk production, work & growth

Poultry (ME)
- Easy to measure, since urine and faeces are voided together
- Less fibre in diet, limited range of feeds

Dogs & cats (ME)
- Effectively linked to BW

Pigs (DE)
- Rationale, simpler system than ruminant with less fibre in diet & limited range of feeds

Horses (DE)
- Calculated based on BW basis

Question 15

Which nutrient has the greatest nutrient density?

Answer 15

Fat

Question 16

Which nutrient provides the most energy in farm animal nutrition?

Answer 16

CHO

Question 17

What are the 2 components of Metabolisable protein (MP) system in ruminants?

Briefly describe the two.

Answer 17

1. Digestible microbial true protein (DMTP)
   - Synthesised by microbes in rumen
   - digested in abomasum & SI
2. Digestible undegraded feed protein (DUP)
   - Fraction of feed not degraded during passage through rumen
   - digested in abomasum & SI

Question 18

What are the 2 components of Feed crude protein?

Answer 18

1. Rumen degradable protein (RDP)
   - Fraction of feed CP that can be degraded in rumen
2. Undegradable dietary protein (UDP)
   - Fraction of feed that is not degraded in rumen
   - Digested in abomasum & SI

Question 19

Briefly summarised how true proteins are synthesised.

Answer 19

1. Rumen degradable protein
2. Effective rumen degradable protein (ERDP)
3. Microbial crude protein (MCP)
4. Microbial true protein (MTP) synthesise by microbes

Question 20

How is crude protein determined?

Answer 20

Measuring Nitrogen (N) content of feed

Question 21

Why is crude protein 6.25 x N?

Answer 21

Because protein contains 16% N

Question 22

Briefly describe how the level of crude protein in foods is determined, and why is it called “crude” protein.

Answer 22

Protein content - calculated from analysing N content of a substance (feed, faeces, excreta), expressed in g/kg fresh or DM;

Protein contains 16% N - N multiplied by 6.25 to get crude protein;

2 assumptions are made: All N present = protein; all protein contains 16% N

Both assumptions are unsound, since not all N in feed is protein, and that different feed proteins have different N contents. So crude protein level is normally an overestimation.

Question 23

Briefly describe the effect of maturation on cell content to cell wall ratio and grass nutritional value.

Answer 23

Grass nutritional value decrease with growth because the older grass contains more lignin;

Cell contents (as grass matures):
- Protein level reduced
- Lipid level reduced
- Mineral level reduced
- NSC level increased!!!

Cell wall:
- Hemicellulose increased
- Cellulose increased
- Lignin increased

Question 24

What would be the best time of the day to cut grass for conservation purposes, and briefly why.

Question 25

Briefly explain how and why supplementary feeds are often processed.

Answer 25

Cereal grain processing: Improves availability of nutrients i.e. increase nutritional value e.g. Cattle & sheep - Better rumen degradability - Prevents grains passing to abomasum undigested E.g. Improves SI digestibility Simple mechanical processing - Rolling, grinding More sophisticated techniques: - Micronisation (heat & mechanical pressure; infrared techniques) - Extrusion (high temperature & pressure, with or without steam)

Question 26

Name 5 factors that can affect the digestibility of a foodstuff, and briefly outline why each does

Answer 26

1. Food composition (chemical composition) - Cell contents are highly digestible - For cell wall, digestibility of fibrous fractions depends on quantity and chemical form 2. Food processing - Treatment e.g. rolling, grinding, chopping, cooking - Chemical treatment e.g. alkali or urea treatment increase digestibility of straw 3. Level of feeding - Especially important in ruminants, since rumen retention time is sensitive to level of feeding; the higher the level of feeding, the lower the rumen retention time(faster); Reduced exposure time of feeds to microbial degradation 4. Ration composition - Associative effects i.e. when 2 or more feeds fed together, digestibility of each feed is affected (usually negative); greatest impact when combining roughage with high starch concentrate 5. Animals - Food digested differently in different species e.g. digestibility of low fibre foods in ruminants an non-ruminants is relatively similar; digestibility of high fibre food is better in ruminants; sheep digests cereal better than cattle, but cattle digest low quality roughage better than sheep

Question 27

Briefly describe partitioning of food energy in animals (use a diagram if you want)

Answer 27

Gross energy - faecal energy = Apparent digestible energy Apparent digestible energy - (urine + gaseous energy) = Metabolisable energy Metabolisable energy - heat increment* = Net energy *Heat increment from digestion/metabolism

Question 28

Briefly describe the metabolisable protein system used in ruminant feeding.

Answer 28

Metabolisable protein (MP) = DUP (digestible undegradable protein) + DMTP (Digestible microbial true protein) DMTP - Synthesised by microbes in rumen - digested in abomasum & SI 1. Rumen degradable protein 2. Slowly degradable & quickly degradable 3. Forms microbial crude protein 4. Forms microbial true protein DUP - Fraction of feed not degraded during passage through rumen - digested in abomasum & SI

Question 29

Briefly describe the basis for ration formulation, and what type of questions need to be asked.

Answer 29

Ration formulation = Feed ingredients combined to provide animal with required nutrients Basis: - Combine ingredients to meet energy requirements - Adjust to meet protein/AA requirements - Check major minerals (supplement if required) - Check trace mineral/vitamins Requires knowledge of: - Nutrient requirements - Feedstuffs available - Feed intake achieved - Any ingredient limitations