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Impacts of Spatial Patterns in Pasture on Animal Grazing Behavior, Intake, and Performance

^a School of Agriculture and Food Systems, Univ. of Melbourne, Victoria 3010, Australia
^b AgResearch Grasslands, Private Bag 11008, Palmerston North, New Zealand
^c Dep. of Horticulture and Crop Science, Ohio State Univ., 2021 Coffey Rd., Columbus, OH 43210, USA
^d Meat and Livestock Australia, 165 Walker Street, North Sydney, NSW 2060, Australia
^e Primary Industries Research Victoria, Dep. of Primary Industries, Private Bag 105, Hamilton, Victoria 3300, Australia
^f Institute of Grassland and Environmental Research, North Wyke, Okehampton, Devon, EX20 2SB, UK

View larger version (13K): [in this window] [in a new window]   Fig. 1. Fitted curves for rumen ammonia concentration of previously-fasted sheep grazing white clover (——), perennial ryegrass (– - – -), Lotus corniculatus (— - - —), perennial ryegrass followed by white clover (. . . . .), or white clover followed by perennial ryegrass (– – – –) for 2 h (0–120 min). Data are adjusted for the crude protein intake (CPI) of individual sheep. From Marotti (2004).

View larger version (17K): [in this window] [in a new window]   Fig. 2. The regrowth dynamics of temperate, grass-based pastures. Unique regrowth curves (only two shown here, Curve 1 from a low residual state and Curve 2 from a greater residual state) depend on the initial state of each patch, Wi, and there is an optimal time of harvest for that patch (denoted t*def) where a straight line drawn from the intercept with the x axis first touches the curve (Parsons and Chapman, 2000). At even greater residual patch states, regrowth is monotonic, implying the patch should be regrazed immediately.

View larger version (152K): [in this window] [in a new window]   Fig. 3. Example of spatial heterogeneity in pasture mass, in a pasture continuously grazed by sheep.

View larger version (18K): [in this window] [in a new window]   Fig. 4. The complex effects of partial preference and of low, medium, and high (specific) foraging costs on the proportion of preferred food in the diet, in relation to its abundance in the vegetation, as predicted by a model that seeks the optimal trade-off between the benefits and costs of foraging selectively (Thornley et al., 1994). Solid diagonal line: high foraging costs; dashed curved line: moderate foraging costs; solid curved line: low foraging costs.

View larger version (23K): [in this window] [in a new window]   Fig. 5. The effect of residual patch state on the maximum sustainable yield that may be achieved and the defoliation interval required to achieve this (solid lines) as predicted by a model that seeks optimal solution for all combination of residual patch state and the timing of harvest. (a) the combinations of residual patch state and defoliation intervals that emerge (separate point for each of a range of stocking rates) when animals are assumed to graze patches either at random (solid dots), or in strict sequence (open circles) and in (b) the same for rotational grazing (open symbols, 30 d with animals not present: 1 d grazing) compared to continuous grazing (solid symbols). Arrows show the direction of increasing stocking rate. After Parsons and Chapman (2000).