Grazing Systems

Fundamentals of Grazing Management

• Importance: Grazed grass is the lowest-cost feed source. Proper management increases forage yield, improves nutrient cycling, reduces parasite loads, and supports carbon sequestration and biodiversity.

• The Grazing Gearbox: Grazing is a complex biological system involving interactions between Soil, Pasture, and Livestock.

• Defining Management Types (Allen et al, 2011):

  • Extensive: Low labor/capital, large land areas per animal.

  • Intensive: High labor/capital to increase production per unit area via higher stocking rates and forage utilization.

Defining Grazing Systems and Intensity

• Grazing System: An integrated combination of soil, plant, animal, social, and economic features and stocking methods to achieve specific goals.

• Stocking Method: A technique to manipulate animals in space and time.

• Control Measures:

  • Forage Allowance: $DM$ per unit animal Live Weight ($LWt$).

  • Grazing Pressure: Animal $LWt$ per unit of forage $DM$.

  • Grazing Frequency: Frequency of defoliation (e.g., continuous vs. rotational).

  • Timing: Based on physiological growth stage (maturity).

Pasture Quantity and Quality

• Optimal Nutrition: Ideal grazing occurs at the 3rd leaf stage when the plant is in a vegetative state.

• Maturity Impact: As plants mature, the proportion of stem increases while leaves decrease, raising poorly digestible cell wall content and decreasing digestible cell contents.

• Measurement:

  • Quantity: Pasture cover ($kg\,DM/ha$, $cm$) or Yield ($t\,DM/ha$).

  • Quality: Measured by sward condition (live:dead ratio) and nutritive value (D-value, $ME$, $CP$, $ADF$, $NDF$).

• Animal Performance: Grazing can support growing beef cattle at $1.0\,kg/d$, growing lambs at $150-250\,g/d$, and milk yields up to $25\,L/day$.

Comparison of Grazing Strategies

• Set-stocking / Continuous: Low labor and capital; higher risk of overgrazing and parasite burden. Usable yield: $4.3\,t\,DM/ha$.

• Continuous (Variable): Management of sward heights. Usable yield: $5.1\,t\,DM/ha$ ($+20\%$).

• Rotational: Fenced areas moved every 3–7 days with 21–28 day recovery. Usable yield: $6.6\,t\,DM/ha$ ($+56\%$).

• Paddock / Mob: High intensity, move every 1–3 days. Provides highest yield and utilization. Usable yield: $8.2\,t\,DM/ha$ ($+92\%$).

Specialized Grazing Systems

• Leader-Follower: High-demand animals graze fresh grass first, followed by lower-demand stock to improve utilization and parasite control.

• Deferred Grazing: Paddocks are closed in late summer to accumulate grass for autumn/early winter. Suitable for dry stock in good BCS (e.g., suckler cows at BCS 3) with grass values of $7-9\,ME$.

• All-Grass Wintering (AGW) for Sheep: Managed rotation from 3 weeks post-mating to 3 weeks pre-lambing. Requires $1\,kg\,DM/d$ (pre-scanning) to $1.5\,kg\,DM/d$ (post-scanning). Potential savings: $\pounds15-18$/ewe/winter.

• Mob / Adaptive Multi-Paddock: High stock density with long rest periods; emphasizes soil health and biodiversity.