20 March 1998


Managing the transition from

winter rations to grazing

after turn-out requires care to ensure milk production is

maintained and to safeguard

fertility. Jessica Buss reports

DESPITE low milk prices this spring, producers must consider supplementing fresh calvers with concentrates to avoid grass staggers.

That is the view of SACs David Roberts, head of dairy research at Crichton Royal Farm, Dumfries, although he does intend to reduce concentrate use after turnout this year.

"While grazed grass is the best quality feed to give cows and the best time to cut concentrates is when cows are at grass, consider offering magnesium supplements to avoid staggers. One cow lost from staggers could outweigh the saving from cutting concentrate in spring."

He advises careful grouping of cows to ensure concentrates are only fed to those that will benefit. Late lactation cows have a low risk of staggers and should be able to get all their feed from grass, allowing concentrates to be reduced quickly.

However, Dr Roberts advises taking extra care with later lactation animals still giving high yields, to ensure magnesium intakes are adequate.

Early lactation cows are at highest risk of staggers, and cannot eat enough grass to sustain their milk production. "When a cow giving 40 litres has concentrates cut to 3kg she must support 32 litres off grass," he says.

That is difficult without loss of body condition and any condition loss could cause poor fertility. Still cut concentrates, he advises, but check cow condition, and be more flexible when it starts to fall, or weather worsens.

At Crichton Royal cows will be fed relatively small amounts of concentrate to carry magnesium. But it will be a good quality concentrate of 18% crude protein fed through the parlour, says Dr Roberts.

When possible, he suggests feeding a straight feed or simple blend through the parlour to reduce costs. But it must be palatable and high in energy.

Silage, however, is of no benefit to cow performance when enough grass is available and when silage fed is of poor quality it can reduce milk proteins. But it can allow a tighter stocking rate, when there is a decline in grass growth rate.

It is also crucial to have a high stocking rate in spring to ensure good quality grass growth in late season. When there is adequate grass, stop buffer feeding, he says. A silage buffer should, however, be reintroduced when bad weather continues for more than a few days.

Sinclair Mayne of the Agricultural Research Institute of Northern Ireland, Hillsborough suggests supplements should also be fed to maintain performance during periods of grass shortage, but that grass silage or hay is likely to be more cost-effective than concentrates. A buffer feed during poor grass growth periods prevents spiralling into shorter grazing rotation lengths.

Dr Mayne suggests that when supplements are fed to improve performance, it is best to feed concentrates, as forages depress grass intakes more than concentrates. Dr Mayne advises producers to target any concentrates to individual cows, by feeding to yield.

But he cites evidence that shows high genetic merit cows can yield 32.5 litres off spring grass without concentrates.

To do so, cows must eat 25% more grass than those yielding 25 litres/day. The higher yielder must, therefore, be provided with tall swards of 14-15cm (5-6in) of high quality grass, so she can eat 18.7kg DM/day. Rotational grazing is needed to achieve such intakes, adds Dr Mayne, who cautions that set stocking a short sward restricts cow intakes to 14-15kg DM.

However, it could still be economic to feed a 40-litre cow 7kg of concentrates at grass. Although the response may only be 1 litre/kg of concentrate, it will improve cow welfare and ensure good fertility. &#42


&#8226 Early lactation cows need magnesium.

&#8226 High yields from grass alone are possible.

&#8226 Use forages when grass supply is restricted.

High genetic merit cows can produce 32.5 litres off carefully managed spring grass without concentrates, according to Sinclair Mayne. But for higher yields still, some concentrate would be needed.

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