Plant Chemistry in Animal Nutrition: Structural and Non-Structural Components

What are the two classifications of plant nutrients?

Structural (cell wall) and Non-structural (storage)

What factors can affect the concentrations of structural and non-structural components in plants?

Genetics, region of plant, growth stage, season, time of day, and environment.

What constitutes the major energy source for herbivores?

The fibrous fraction of the plant, measured as NDF and ADF.

What are the main constituents of the plant cell wall?

Polysaccharides, proteins, phenolic compounds (e.g., lignin), water, and minerals.

What percentage of polysaccharides in the cell wall are structural?

90%

What is cellulose primarily composed of?

Linear polymer of β-1,4-linked D-glucose units.

What is the range of cellulose content in green plants?

Approximately 20-40%.

Which bacteria are primarily responsible for cellulose degradation in the rumen?

Fibrobacter succinogenes, Ruminococcus flavefaciens, and Ruminococcus albus.

What is hemicellulose?

A mixture of linear and branched polysaccharides, less resistant to chemical degradation than cellulose.

What are the main components of pectins?

Branched or coiled D-galactopyranosyl uronic acid units linked with α-1,4 bonds.

What are fructans and where are they typically found?

Storage carbohydrates found in temperate grasses, cereals, and some vegetables.

What is starch and where is it commonly found?

The major storage carbohydrate of many plants, found in cereals, legumes, roots, and tubers.

How does the availability of starch for digestion vary?

It is altered by its association with protein within the seed endosperm.

What happens to the proportion of structural carbohydrates as plants mature?

It increases, leading to lower digestibility.

What are the main types of storage carbohydrates in plants?

Fructan and starch.

What is the significance of microbial enzymes in digesting fructans?

They are required for the degradation of fructans due to specific bond structures.

What role does lignin play in plant digestion?

Lignin is indigestible and affects the overall digestibility of plant materials.

What is the relationship between cellulose and hemicellulose in terms of digestibility?

They represent a significant source of variation in digestibility and nutritional value of ruminant diets.

What is the primary function of the fibrous fraction in animal nutrition?

To provide energy and support digestion in herbivores.

What is the significance of understanding the composition of plant cell walls?

It is essential for optimizing forage utilization and fiber digestion.

What is the effect of processing on the degradation of plant cell wall components?

Processing can influence the nutritional composition and degradation rates.

What are the two main types of carbohydrates found in the intracellular contents of plants?

Fructans and starch.

How does the structure of hemicellulose differ from cellulose?

Hemicellulose is a mixture of linear and branched polysaccharides, while cellulose is a linear polymer.

What is the role of exogenous fiber enzymes in animal diets?

They are used to improve digestibility, mainly in pig and poultry diets.

What is the primary structural component of the plant cell wall?

Cellulose.

How does the digestibility of plant materials relate to their structural carbohydrate content?

Higher structural carbohydrate content generally leads to lower digestibility.

What is the significance of the microbial community in the rumen?

It plays a crucial role in the degradation of cellulose and hemicellulose.

What are the two main polysaccharides that compose starch?

Amylose and Amylopectin

What type of linkages are present in amylose?

α-(1→4)-linked polymer

Why is amylose relatively resistant to amylases?

Due to its tight helices and crystalline packing

What types of linkages are present in amylopectin?

α-(1→4) & α-(1→6)-linked polymer

What is a key characteristic of amylopectin?

It is easily degraded by amylases

What factors affect the accumulation of non-structural carbohydrates (NSC) in plants?

Plant genetics, tissue type, growing stage, time of day, environment, and management

How does the growth stage of pasture affect NSC levels?

Early spring has higher growth and lower NSC; late spring/summer has lower growth and higher NSC

What time of day do non-structural carbohydrates peak in plants?

Late afternoon/early evening

What is lignin and why is it significant in plants?

A phenolic polymer that provides structural strength and is resistant to degradation

How does lignin affect the digestibility of other nutrients?

It reduces the digestibility of nutrients it is associated with

What is the relationship between lignin and cellulose?

Lignin is highly associated with cellulose and hemicellulose

What is the formula for calculating crude protein?

Crude protein = Nitrogen content × 6.25

What is the primary source of true protein in leaves?

The photosynthetic enzyme RuBisCO

What is non-protein nitrogen and where can it be found?

Includes nitrate, amides, free amino acids, and peptides, found in young, heavily fertilized grass

What does proximate analysis measure in plant feed?

Dry matter, organic matter, ash, crude protein, lipids, starch, and fiber

What does NDF stand for and what does it indicate?

Neutral Detergent Fiber; it indicates gut fill and intake

What does ADF stand for and what does it indicate?

Acid Detergent Fiber; it indicates digestibility

What does ADL stand for and what does it measure?

Acid Detergent Lignin; it measures lignin content

Why is lignin nutritionally important despite not being a carbohydrate?

It is indigestible and affects the digestibility of other nutrients

Why does amylopectin digest faster than amylose?

Because amylopectin has both α-1,4 and α-1,6 linkages, making it more accessible to enzymes

What is the significance of the Kjeldahl digestion method?

It calculates crude protein based on nitrogen content

What does the term 'crude fiber' under-read in plant analysis?

It under-reads the actual fiber content, which includes NDF, ADF, and lignin

What is the impact of alkali treatments on lignin?

They do not degrade lignin but can separate it from structural carbohydrates, enhancing digestion

What are the three common monolignols that make up lignin?

Paracoumaryl alcohol, coniferyl alcohol, and sinapyl alcohol

What is the effect of light and temperature on non-structural carbohydrate levels?

They affect the balance between photosynthetic activity and utilization

What is the role of fungal fibrolytic enzyme preparations in digestion?

They have been tested to improve digestion of high-lignin tropical forages

What does the term 'dry matter' refer to in proximate analysis?

The weight of the feed after removing moisture