Pasture and Grazing Systems Synthesis

Synthesizing Pasture and Grazing Systems

• The primary goal of the tenth week of teaching is to synthesize concepts covered throughout the trimester, bridging the gap between pasture production (growing a productive pasture) and utilization (effective animal grazing management).

• Over the last ten weeks, the unit has deliberately focused on temperate high-production systems from a pasture production perspective to explore landscapes where pastures can be improved through establishment and nutrition.

• Grazing components have often focused on tropical pasture swards, where constraints like sward structure (ratio of leaf to stem) impact production.

• This lecture aims to find the "middle ground," identifying similarities and differences between temperate and tropical systems to provide a balanced overview of the livestock production cycle.

The Pastoral Sward

• Definition: A pasture sward is a combination of different plant species making up a population or community of plants within a specific area.

• The sward exists at the vital interface between pasture production (growing feed) and animal management (utilizing feed).

• Production Perspective: The goal is to maximize the production of high-quality, palatable feed with sufficient ground cover and persistence.

• Animal Perspective: The sward structure directly influences animal response. Factors include:

  • Leaf-to-stem ratio.

  • Morphology and physiology of the plants.

  • Patterns of growth and herbage accumulation.

  • Population dynamics.

  • Ingestive behavior, herbage intake, and resultant animal performance.

• Management Feedback Loop: It is not just that the sward impacts animals; grazing management uses animals to manipulate the sward into a specific state that is more productive for the overall grazing system.

Sward Control and Grazing Management Targets

• Manipulating sward structure allows producers to predict animal production and maintain long-term control over pasture species composition.

• Control Challenges: Achieving a high level of control is difficult and depends on the system type.

  • Intensive Systems: (e.g., dairy systems with $0.5\,\text{ha}$ paddocks and $10\,\text{cows/ha}$) allow for homogeneous grazing and easy movement of cattle to maintain precise sward patterns.

  • Extensive Systems: Characterized by low stocking rates and large areas. Mustering is difficult, making sward control less effective. Techniques like the placement of water points are used to stimulate animal movement to specific areas.

• Economic Payoff: Higher levels of control usually pay off better in high-production systems. In low-productivity or harder-to-manage areas (unsuitable for cropping), the challenge of management is heightened but rewarding.

Hierarchy of Influence in Pasture Productivity

• Climate and Soil Type: These are the primary drivers of productivity. Climate is the first influence, followed by soil type. They dictate what species can grow, when they grow, and which species should be selected for pasture improvement.

• Supply and Demand Gap: There is rarely a consistent supply of feed. Producers must manage extremes, such as:

  • Wet and dry seasons in tropical regions.

  • Rainfall-rich summers versus cold winters in temperate regions (e.g., Armidale).

• Species Selection: Swards are generally diverse (grasses, legumes, herbs). Selection must consider:

  • Suitability to climate and soils.

  • Compatibility between species (growing together).

  • Adaptation to specific management (e.g., choosing a white clover cultivar with specific leaf size based on whether sheep or cattle will graze it).

The Growth Curve and Management Decisions

• The grass growth curve consists of three phases:

  • Phase 1: Slow growth, very high quality, low biomass.

  • Phase 2: Rapid growth, increasing biomass, leaf area expansion, but declining quality.

  • Phase 3: Growth plateaus/slows, quality decreases significantly.

• Grazing Targets: Most management recommendations aim to graze pastures between Phase 2 and Phase 3.

• Identification of Targets:

  • Ryegrass: Use the "three-leaf stage" as a indicator for grazing.

  • Tropical Pastures: Use specific sward height targets.

Economics and Productivity

• Australian Context: Land prices in Queensland have increased by approximately $16.6\%$ per year over the last 20 years, while beef production has only increased by $0.54\%$.

• Beef prices increased by about $5\%$ in the same period.

• Competitive Strategy: As profit margins shrink, the only way for farmers to survive is to increase on-farm productivity (e.g., $kg$ of beef per hectare, $L$ of milk per hectare, or $kg$ of wool per hectare).

• Key Performance Indicators (KPIs): Benchmarking often focuses on productivity per hectare and productivity per millimeter ($mm$) of rain received.

Temporal Dynamics and Monitoring

• Pasture swards are dynamic and change year-to-year based on climate and management.

• Farmlet Case Study Data: A comparison of three farmlets (A, B, and C) showed that management significantly impacts sward composition, including:

  • The proportion of sown vs. volunteer species.

  • The proportion of native vs. introduced species.

  • Physiology ($C_3$ vs. $C_4$ species).

• Important Metrics for Monitoring:

  • Total Herbage Mass: Total biomass produced.

  • Legume Proportion: Influences nitrogen cycling and animal health risks (e.g., bloat).

  • Animal Demand: Changes over time based on livestock class and growth.

Practical Paddock Design and Water Management

• Water as a Focal Point: The watering point is the key driver of animal behavior.

  • Extensive systems: Guideline of no more than $7\,\text{km}$ between watering points.

  • Southern/High-production systems: Points should be much closer to minimize energy expenditure from walking (maintenance costs).

• Centralized Watering: Utilizing one trough for multiple paddocks (e.g., four paddocks rotating around a central trough) minimizes capital investment in fencing and infrastructure.

• Water Quality: Clean water (reticulated to troughs) leads to better animal performance and liveweight gain compared to dirty or muddy water from dams.

• Subdivision Principles:

  • Subdivision does not grow more pasture, but it increases utilization efficiency.

  • Fencing Guidelines: Fence according to soil type (e.g., Basalt vs. Granite) and terrain/aspect (e.g., north-facing vs. south-facing slopes).

  • Paddock Shape: Square paddocks generally lead to more even utilization than irregular shapes.

• Number of Paddocks Calculation: A rough starting point is based on the grazing cycle: $\text{Number of Paddocks} = \frac{365}{\text{Days on Paddock}} \times \text{Expected Grazing Cycles}$.

Utilization and Regrowth Principles

• Utilization Rates:

  • National average is approximately $30\%$.

  • Rangelands may recommend levels as low as $10-15\%$.

  • High-production systems (e.g., dairy or plantain/clover mixes) can reach $60-70\%$.

• The "Fat in the System": Over-utilizing can be problematic during dry years; maintaining some residual biomass provides a buffer.

• Residual Biomass: "Leave leaves to grow leaves." More green leaf area serves as solar panels for photosynthesis and carbohydrate production.

• Nutrient Replacement: Systems with high utilization rates ($70-80\%$) must replenish nutrients via fertilization, or the system will fail over time.

Three Levels of Management

1. Feed Profile (Long-term): Matching feed demand and supply based on average years and carrying capacity (e.g., the Consultancy Briefing assignment).

2. Feed Budget (Medium-term, 3-6 months): Responding to specific seasonal conditions (e.g., deciding to buy or offload stock based on rainfall and biomass).

3. Grazing Plan (Short-term, daily/weekly): Implementing the budget at the paddock level, determining specific grazing durations and stocking density.

Standardizing Demand: Dry Stock Equivalents (DSC)

• DSC ratings standardize animal requirements.

• Requirements are not static; as an animal grows, its DSC rating increases.

• Weight Example: Sheep growing from $35\,\text{kg}$ to $70\,\text{kg}$ will see a corresponding increase in DSC requirement.

• Marketing percentages in breeding ewes also influence the total DSC rating of a flock.

The Feed Wedge

• Primarily used in high-production dairy systems (e.g., New Zealand).

• Visual Depiction: X-axis shows paddock numbers (ranked by biomass); Y-axis shows biomass levels.

• Management Utility: Helps identify gaps or excesses in feed.

  • If feed exceeds the target line (e.g., above $2700\,\text{kg}$), the producer might conserve it as hay or silage.

  • If feed falls below the residual line (e.g., $1500\,\text{kg}$), supplementation is required.

Ecological Interactions in Grazing Systems

• A grazing system is an ecosystem operating at four levels: Individual organism, Population, Community, and Ecosystem.

• Dynamic Balance: Management acts as a manipulator of the ecosystem balance.

  • Example: Grass/Legume pairings. Phosphorus fertilizer can favor legumes. Frequent Nitrogen fertilizer can make grasses more competitive and shift the balance.

• Stability in species composition and production is the ideal goal, which is achieved primarily through effective grazing management rather than just the plants themselves.

Questions & Discussion

• Question regarding Livestock Enterprises: If you change from fine wool Merinos to trade cattle, how does the feed selection shift?

  • Response: The feed type is often suitable for most livestock, but the trade-off is between productivity and persistence. Some species, like Bambatsy panic, can cause photosensitization in certain livestock classes. Usually, there isn't a "wholesale shift" in species, but the management package (when to graze, how much pressure) must change.

• Question regarding Riparian Access: Should animals drink directly from creeks/waterways?

  • Response: This is case-by-case. In high-intensity systems, cattle pressure can degrade water quality and riparian zones, so fencing off creeks and pumping to troughs is ideal. In very extensive systems, this level of infrastructure may be logistically impossible. Research shows clean water improves liveweight gain compared to muddy dam water.