25 July 1997

Rotation is key to growth

Rotational grazing of beef cattle can help to sustain growth rates into the second half of the grazing season. Jonathan Riley reports

BEEF producers who fail to implement a rotational grazing system are missing the chance to achieve average growth rates of over 1.22kg/day from grass alone throughout the grazing season.

It is relatively easy for any grazing system to achieve high cattle growth rates in the spring because of an abundance of grass, says Terry Carroll of the Irish advisory service Teagasc. But, from July onwards, grass growth and quality declines making it more difficult to sustain growth rates.

"The grass growth curve is often portrayed as a gently undulating line with peaks in spring and autumn.

But, in practice grass growth varies daily according to temperature and moisture and cattle can easily be under or over stocked as the weather changes," he says.

"Set stocking regimes and a rigid conservation policy create a system which cannot react quickly enough to changes in grass growth, leading more readily to under or over stocking," says Mr Carroll.

By contrast, dividing the grass areas into small paddocks and implementing a rotational grazing regime restricts the grass area available to the cattle so that all grass within a paddock is taken down evenly.

This creates obvious blocks of feed and grass height can be measured using a rising plate meter. Combining this with estimated feed intakes for growing cattle, the number of days of feed available in a paddock can be established.

Excess grass can then be earmarked and made into silage or shut up to extend the grazing season.

Set stocking and rigid forage conservation policies create a system which cannot react quickly enough to changes in grass growth, according to Irish grassland adviser Terry Carroll.

GRAZING RESEARCH

&#8226 A 500kg beef animal consumes 11.25kg drymatter of grass a day.

&#8226 Cattle on set stocked pasture spend three times longer roaming the field without grazing than in rotational grazing systems.

&#8226 Grass heights for beef cattle are optimal down to 5cm.

&#8226 Grazing silage ground before first cut reduces yields by 15%, but rotational grazing at this time improves digestibility by five points and boosts second cuts.

&#8226 Grazing can be extended by five weeks without causingsoil damage.

&#8226 Grass intakes on rotations are higher and an extra 15kg liveweight can be achieved.