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Animal selection

Spray-grazing requires the removal of as much of the weed as possible. Sheep are more effective in achieving the desired grazing height than cattle because they graze closer to the ground. Grazing with cattle to a maximum pasture height of 4cm is a minimum target and lower heights are desirable when grazing with sheep.

The pasture must be grazed down to reduce the chance of weeds growing back due to residual sugars in the uneaten leaves.

The effect of reduced intake as feed on offer declines is partially offset by the high quality of the weeds being eaten (Figure 2).

Where possible, avoid grazing with animals with metabolic sensitivities, such as late-pregnant ewes or cows, or animals in light condition.

In a spray-grazing paddock demonstration run by Southern Farming Systems at Inverleigh, Victoria, animals gained weight. Composite lambs gained 410g/ head/day over a 21-day grazing period and ewes maintained a condition score of 3.3-plus.(Brogden, 2020)

Figure 2: Energy content (MJ ME/kg DM) for spray-grazing target weeds throughout the growing season.