3 September 1999


BUILDING grass in front of cows must be the main priority during September to ensure plenty to graze later in autumn when growth declines.

Each extra day spent grazing in autumn or spring will earn £1 a cow a day, according to research from the Agricultural Research Institute of Northern Ireland at Hillsborough. The saving – achieved from as little as two and a half to three hours grazing a day – is due to reduced silage and concentrate inputs, extra milk production of up to two litres a cow a day, and improved milk quality (see below).

British Grassland Society consultant, Carol Gibson, says similar savings have been seen on farms she visits in the north of the UK and Wales. "When pastures have been well maintained over the year, autumn grass is still as good quality as silage with an ME of at least 11, and its cheaper."

Being able to keep cows out longer in autumn depends on building pasture covers from September. She advises lengthening the grazing rotation to 40 days in September to achieve this.

"Graze all areas accessible to cows, and avoid taking any late cuts of silage unless cows cant possibly eat it."

The longer rotation will allow average grass covers to increase by ensuring pasture intake is less than growth in this period. This allows a fast build up of pasture cover in-front of cows through September, says Ms Gibson.

"The slow rotation is important. Even when theres little grazing, keep cows tight behind the electric fence. This will ensure you build up loads of grass while its still growing so theres plenty to graze later on."

When its been dry, covers might be quite low in early September, she warns. "It may be necessary to introduce supplements – if youre going to get an economic response to supplements this is the best time to do it."

Average farm cover should rise to 2600kg DM/ha by late September for spring calving herds; autumn calving herds should aim for 2300kg DM/ha of cover when there are relatively few cows in milk in early autumn.

"This standing buffer of grass or feed wedge for grazing in October and November sounds huge but because its late in the year – and provided the grass has been well managed through autumn – it will all be leafy and green so cows will graze it readily."

Ms Gibson recommends applying nitrogen when necessary to secure target covers. Grass grows as fast in September as it does in March (see above) – so any nitrogen put on will still be used, provided theres a months good growing conditions ahead of the application.

"N uptake is higher on soils lacking N. Many farmers extending the grazing season and minimising silage made will have applied lower nitrogen rates over summer. This will tend to give improved nitrogen uptake in late season.

"Probably only relatively light dressings will be needed – 20-30 units/acre should be adequate to build up covers for grazing in October and November."

However, Ms Gibson cautions that there is no point in building up covers when there arent adequate tracks to support extended grazing, especially on a wet farm, and when grass quality is poor due to lax grazing earlier on.

To ensure grass quality is still excellent by the end of September, cows should be grazing down to 1600kgDM/ha. "Use dry cows to help when necessary."

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