ANSC 433 Lecture Notes - Lecture 15: C3 Carbon Fixation, C4 Carbon Fixation, Bromus Inermis
23 May 2018
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15. ANSC 433: Animal Nutrition & Metabolism
1
Feedstuffs – Forages and Roughages
Official NRC Categories of Feeds
- Dry forages & roughages
- Pasture, range plants & forage fed green
- Silages
- Energy feeds
- Protein supplements
- Mineral supplements
- Vitamin supplements
- Non-nutritive additives
Forages
- Vegetative portion of plants consumed by animals
- Roughages: less digestible, fibrous feeds with over 18% CF including forages, by-products and crop residues
- Examples of forages
o Hay, haylage, silage, straw, fodder, browses
Grasses
- Cool season or temperature grasses
o C3 photosynthetic pathway
o Growth starts at 0oC; maximum at 20oC
o Examples: ryegrass, smooth brome grass
- Warm season or tropical grasses
o C4 photosynthetic pathway
o Growth starts at 10oC; maximum at 30-35oC
o Examples: bermudagrass, Bahiagrass
- Cereals (wheat, barley, oats and rye) can be used as pasture during vegetative growth
o Earl sprig, pasture does’t reall ipair groth of ereals
Legumes
- Characterized by ability to fix atmospheric N
- Alfalfa (Medicago sativa) is by far the most widely used legume for pasture, hay-crop and hay in NA
o High yield
o High palatable
- Other legumes used include:
o Red and white clover
o Birdsfoottrefoil
- Some legumes can cause frothy bloat – entrapment of gases in rumen that causes asphyxiation
- …
Chemical Composition of Forages
Carbohydrates
- Non-structural
o Tropical grasses (C4) and legumes accumulate sucrose and starch
o Temperate grasses (C3) accumulate sucrose and fructosans
- Structural: tropical grasses are higher in fiber than are temperate forages
Protein
- Legumes are higher in protein than grasses, particularly in more mature plants
o Has to do with C3 and C4
- The leaves are rich sources of protein and other nutrients, but stems, which are high in cellulose and lignin are of much lower
value, especially in mature plants
- Forages that contain tannins have a high level of rumen-protected protein, such as legumes
Minerals
- Legumes have high concentrations of Ca, Mg and S
- Legumes tend to be lower than grasses in Mn and Zn
find more resources at oneclass.com
find more resources at oneclass.com
15. ANSC 433: Animal Nutrition & Metabolism
2
Factors Affecting Forage Quality
- Stage of maturity
o Most important factor influencing the composition and nutritive value of pasture
- Plant factors
- Climate
- Management
- Antinutritive factors
- Harvest and storage conditions
Effects of Stage of Maturity on In Vivo Measures of Alfalfa Forage Quality
- Stages of maturity: early to mature
- For alfalfa maturity
- Decrease in digestibility = decrease in intake and
production
Plant Factors
Anatomy
- Tropical (C4) grasses have more bundle sheath cells and less
mesophyll, and are less digestible
o Tight compactness makes it less available to the
microorganisms making it less digestible
- Whereas temperate (C3) grasses have the opposite
Chemical Composition
- Greater cell wall & lignin concentrations are usually associated with poorer forage quality
o As plant grows, need more support to hold the plat’s ass ad proteis
Lead to Stem Ratio
- Thicker stems or lower lead to stem ratios generally imply greater cell wall concentrations
Differences in Leaf Anatomy
- C3 (left) = less organization
(uniformity) and space between cells
- C4 (right) = more compact and
organized
Climatic Factors
- Temperature
o High temperatures favour cell
wall deposition whereas lower temperatures favour sugar deposition
o Sudden frost can lead to accumulation of toxins like nitrates
▪ Which is something that causes reduced growth of the plant
- Moisture
o Droughts can limit the cell wall deposition and increase nitrate accumulation
- Sunlight
o Inadequate photoperiod can cause senescence and sugar and N losses from plants
- Can harvest higher up on the plant since the N concentrates in the bottom part of the plant
Management Factors
- Fertilization
o N fertilization can increase plant CP %
- Maturity/regrowth interval
o Generally cell wall deposition and lignification increase with maturity/regrowth interval
- Cutting height, plant spacing, etc. may also affect quality
o Won’t go into detail just bear in mind that management factors will affect the quality of the plant
Anti-nutritive Factors
- Condensed tannins
o Plant phenolic compounds that can limit nutrient availability to animals
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Roughages: less digestible, fibrous feeds with over 18% cf including forages, by-products and crop residues. Examples of forages: hay, haylage, silage, straw, fodder, browses. C3 photosynthetic pathway: growth starts at 0oc; maximum at 20oc. C4 photosynthetic pathway: growth starts at 10oc; maximum at 30-35oc. Cereals (wheat, barley, oats and rye) can be used as pasture during vegetative growth. Earl(cid:455) spri(cid:374)g, pasture does(cid:374)"t reall(cid:455) i(cid:373)pair gro(cid:449)th of (cid:272)ereals. Alfalfa (medicago sativa) is by far the most widely used legume for pasture, hay-crop and hay in na: high yield, high palatable. Some legumes can cause frothy bloat entrapment of gases in rumen that causes asphyxiation. Tropical grasses (c4) and legumes accumulate sucrose and starch. Structural: tropical grasses are higher in fiber than are temperate forages. Legumes are higher in protein than grasses, particularly in more mature plants: has to do with c3 and c4.
