Selective Grazing and Grazing Management Lecture Notes

Overview of Topics - Lecture 1: Selective grazing and its impact on production systems. - Lecture 2: Introduction to grazing management across three sessions.

Understand selective grazing vs. preference.
Discuss what animals select in various grazing scenarios.
Examine animal factors affecting diet selection.
Explore implications for grazing management and manipulation of grazing preferences.

Preference: - Defined as what an animal would eat if unrestricted. - Analogy: Choosing a meal without any dietary constraints.
Selection: - Actual choices made by animals based on available options in their environment. - Example: An animal may prefer clover but may have to select grass due to its scarcity in the environment.

Animals tend to select a diet with a higher nutritional value compared to what's generally available in their grazing area.
Variation in availability of pasture diversity influences diet selection.

Monoculture (Grass Only): - Animals prefer grazing the top of the sward where younger leaves are available. - These younger leaves contain higher nutritional value (higher digestibility and crude protein).
Grass and Legume Combination: - Animals show a strong preference for legumes over grasses. - In a grazing trial, animals consumed approximately 70% legumes and 30% grasses when allowed to select freely. - The proportion of legumes in their diet is consistently higher than what’s available in the paddock.

Despite an apparent preference, animals' consumption patterns change throughout the day and across different animal categories.
Consumption of legume tends to be higher in the early part of the day.

Including multiple species in the pasture mix can complicate selection but may offer nutritional benefits.
The balance of what animals select can have long-term agronomic implications.

Choice Trial (Grass vs. Mixture): - Animals with mixed species had lower nutritional intake compared to those with a single preferred option (rye grass). - Animals prefer diverse forage; however, their nutritional output could be lower if their selection is based more on volume than quality.
Sequential Offering: - Varying combinations of forage offered throughout the day influenced the intake of different animal types. - For example, offering chicory and lucerne first in the day led to higher intake compared to other combinations.

The physiological history and current health of the animal heavily influence dietary preferences.
Example: Sheep infected with gastrointestinal nematodes were found to prefer higher protein diets which indicates their ability to detect and correct dietary deficiencies.

Grazing Pressure: Can affect which species are consumed. A well-managed system can prevent overgrazing of desirable species and encourage more uniform consumption across the pasture.
Stocking Rate vs. Stocking Density: These concepts can influence long-term sustainability of the grazing system. Higher densities can lead to selective pressures that affect pasture composition and health.

Several grazing systems exist: - Continuous Grazing - Rotational Grazing - Various methods (e.g., cell grazing, mob grazing, etc.).
The approach should be tailored to specific environmental conditions and production goals.

Stocking Rate: The number of animals present in a given area.
Stocking Density: The number of animals per unit area at any given time.
Forage Mass vs. Forage Production: Understanding current biomass vs. what is produced over time.
Carrying Capacity: The maximum number of animals an area can support without degradation.

The relationship between animal preference, selection, and the management of grazing systems is complex.
Key Factors for success: understanding animal behavior, managing plant responses through frequency and severity of grazing, and adapting management strategies to environmental changes.
Importance of Flexibility in management to respond to variations in climate and pasture growth rates.