PRINCIPLES OF NUTRITION Flashcards
What is neutral detergent fibre (NDF)?
- Plant cell wall material
- Fibre insoluble in neutral detergent
- Residue containing CW materials = Hemicellulose + Cellulose + Lignin
What is acid detergent fibre (ADF)?
- Fibre insoluble in acid detergent
- Residue contains CW material = lignin + cellulose
What does NSC stand for?
And what is NSC fraction composed of?
- Non-structural carbohydrates
- NSC fraction composed of Starch + WSC (water-soluble carbohydrates)
What is WSC fraction composed of?
Simple sugars + fructan
State some factors that affect grass growth/productivity and briefly describe them.
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
What are the desirable characteristics of low DM silage?
Low pH, low butyrate, low NH3-N, high lactate
Why is HT forage high in nutritional value?
Young herbage utilised
Rank the starch content of oats, barley and maize from highest to lowest.
Maize, barley, oats
What oilseed meal is most commonly used?
Soya bean meal
What term is most often used for digestibility?
Apparent digestibility
How is in vitro digestibility assessed?
Through work in labs
How does increased feeding level in ruminants change ruminal retention time and thus digestibility?
Reduces ruminal retention time and digestibility
State the relationship between GE (Gross energy), DE (Apparent digestive energy), ME (Metabolisable energy) and NE (Net energy).
GE (Gross energy) is measured by converting food to heat energy;
GE - Faecal energy = DE
DE - (urine + gaseous energy) = ME
ME - heat increment = NE
State the energy system for ruminants, pigs, poultry, dogs & cats, and horses.
Briefly explain why that energy system is used when possible.
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
Which nutrient has the greatest nutrient density?
Fat
Which nutrient provides the most energy in farm animal nutrition?
CHO
What are the 2 components of Metabolisable protein (MP) system in ruminants?
Briefly describe the two.
- Digestible microbial true protein (DMTP)
- Synthesised by microbes in rumen
- digested in abomasum & SI - Digestible undegraded feed protein (DUP)
- Fraction of feed not degraded during passage through rumen
- digested in abomasum & SI
What are the 2 components of Feed crude protein?
- Rumen degradable protein (RDP)
- Fraction of feed CP that can be degraded in rumen - Undegradable dietary protein (UDP)
- Fraction of feed that is not degraded in rumen
- Digested in abomasum & SI
Briefly summarised how true proteins are synthesised.
- Rumen degradable protein
- Effective rumen degradable protein (ERDP)
- Microbial crude protein (MCP)
- Microbial true protein (MTP) synthesise by microbes
How is crude protein determined?
Measuring Nitrogen (N) content of feed
Why is crude protein 6.25 x N?
Because protein contains 16% N
Briefly describe how the level of crude protein in foods is determined, and why is it called “crude” protein.
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.
Briefly describe the effect of maturation on cell content to cell wall ratio and grass nutritional value.
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
What would be the best time of the day to cut grass for conservation purposes, and briefly why.
Briefly explain how and why supplementary feeds are often processed.
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)
Name 5 factors that can affect the digestibility of a foodstuff, and briefly outline why each does
- Food composition (chemical composition)
- Cell contents are highly digestible
- For cell wall, digestibility of fibrous fractions depends on quantity and chemical form - Food processing
- Treatment e.g. rolling, grinding, chopping, cooking
- Chemical treatment e.g. alkali or urea treatment increase digestibility of straw - 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 - 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 - 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
Briefly describe partitioning of food energy in animals (use a diagram if you want)
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
Briefly describe the metabolisable protein system used in ruminant feeding.
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
Briefly describe the basis for ration formulation, and what type of questions need to be asked.
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
