L11 – Forage Value Lecture Notes

Practice flashcards based on the lecture transcript regarding forage value, covering the differences between grazing systems, nutritional parameters, and the physiological differences between C3 and C4 plants.

Who is the lecturer for the sections on plant and animal component integration?

Tiago Silva

In a grazing system, what are the three steps of efficiency where losses occur?

1. Nutrients/resources to plant growth. 2. Pasture produced to pasture harvested by the animal. 3. Pasture consumed to animal product (e.g., meat).

How is 'Quality' defined in the context of animal feed?

Quality is the product of nutritional value (chemical composition) and voluntary intake.

What are the five common parameters used to describe nutritional value?

1. Dry matter digestibility (DMD). 2. Metabolizable energy (ME). 3. Crude protein (CP). 4. Neutral Detergent Fiber (NDF). 5. Acid Detergent Fiber (ADF).

What is the definition of dry matter digestibility (DMD)?

The proportion of the feed consumed that is actually absorbed by the animal (Feed In minus Feces Out).

What device is used to measure the gross energy of a feed sample by burning it?

A bomb calorimeter

How is Metabolizable Energy (ME) calculated?

$$ME = \text{Digestible Energy} - (\text{Urinary Energy} + \text{Methane Energy})$$

What is the largest source of energy loss the animal experiences from its diet?

Fecal energy

Why is the enzyme Rubisco referred to as 'promiscuous'?

Because it can react with both $CO_2$ (carboxylase) and Oxygen (oxygenase) depending on concentration and temperature.

What specific leaf anatomy characterizes C4 plants and protects Rubisco enzymes?

Kranz anatomy

Explain the function of PEP carboxylase in C4 plants.

It acts as a pump that only reacts with $CO_2$, transporting it into bundle sheath cells where Rubisco is trapped, thereby preventing photorespiration.

Why do C3 plants generally have a higher concentration of crude protein than C4 plants?

C3 plants are less photosynthetically efficient and must maintain a much higher concentration of the Rubisco enzyme, which is a protein.

What three components make up Neutral Detergent Fiber (NDF)?

Hemicellulose, cellulose, and lignin

In the 'brick wall' analogy for plant cell walls, which component represents the mortar?

Lignin

How does an increase in temperature typically affect plant nutritional value?

It increases growth and respiration relative to photosynthesis, causing the 'balloon' (cell wall) to be less filled with sugars, thereby increasing fiber and decreasing digestibility.

At what time of day is the nutritional value of a plant usually at its highest?

At the end of the day, after a full day of photosynthesis has accumulated water-soluble carbohydrates.

In a cited trial, how much more weight did heifers gain just by being rotated to new pasture in the evening instead of the morning?

$$150\,g$$

How does mild water stress affect plant digestibility?

It can lead to higher digestibility because there is less turgor pressure on the cell walls, reducing the stimulus for the plant to build stronger, more fibrous walls.

What is a common mistake producers make after applying nitrogen fertilizer?

Not harvesting or grazing more frequently; the nitrogen accelerates plant maturity, which can drop nutritional value if the plant is allowed to become too old.

How do the digestibility ranges of tropical (C4) and temperate (C3) pastures compare?

Temperate pastures are concentrated at the higher end ($60\%$ to $80\%$), while tropical pastures have much higher variability, ranging from $20\%$ to $80\%$ due to morphological changes like stem elongation.

What part of the plant tiller has the highest nutritional value?

Newer leaves at the top of the tiller, as nutrients are translocated to them from older, senescing leaves.