Diet update closes DM gap

TIMELY INTERVENTION by one Norfolk dairy unit, when maize silage turned out to be wetter and lower in starch than expected, has avoided reductions in yields and fertility this winter.

Relying on maize to form a big part of the diet can be risky when quality is not up to scratch. But the team running Hall Farm, Worstead, owned by Gavin Paterson, quickly adjusted its mixed ration when tests showed maize was just 23.9% dry matter and less mature than previous years.

Farm manager Jon Lowe says 81ha (200 acres) of maize is grown as a catch crop with Italian Ryegrass to supply a mix of silages to the 190 cows at Hall Farm, plus a second herd of 170 cows. “We have increased the acreage as grazing dries up in June and milk yields have risen to 9158 litres, to allow buffer feeding all summer.”

Because maize is drilled relatively late – after ryegrass is silaged in early May – mid-maturing varieties are used and these are harvested at a green stage. “Yields range from 12t/acre to 16t/acre,” adds Mr Lowe.

But this year”s wet summer resulted in a crop that grew, yet did not fully mature. Anglian Farmers” nutritionist Rodney Allen says that, despite a fair number of cobs, there were too few heat units to ensure maturity. Maize was harvested on Oct 25 and fed immediately.

Mr Allen estimated the forage”s value so herd manager Shaun Clarke had a ration for the autumn-calving herd. But Mr Clarke, who works on the basis of cow portions, had noticed cows were eating more.

“We were feeding 38 portions of the ration to a 32-cow group, although DM intakes were 24.5kg a cow and cows were milking all right,” he says.

Forage samples confirmed Mr Allen”s suspicions that dry matter and starch were low. Analysis on Nov 2 revealed 23.9% DM, 11MJ/kg of metabolisable energy, 7.6% crude protein and a starch of 25%. A second sample on Nov 11 confirmed a similar DM and ME, but a lower starch of 16.2%.

Plus NDF fibre values were 63% and 61%, reflecting a low cob index, as they were diluted by the bulk of green material.

“Usually maize is 28%-32% DM, so this is on the low side. The other problem is when starch is less than 20%, there is a high level of sugar which has not converted to starch.

“Both samples showed a potentially high acid loading and if we had not reformulated the diet, cows would have milked off their backs, losing more condition after calving than we would like and depressing yields and fertility.”

It would have also hit butterfats, levels of which have climbed to 4.4%, now earning an extra 0.7p/litre on a constituent contract, compared with last year.

There was no radical change made to the diet, just a rebalancing of fresh weights to counteract wetter maize and lower starch levels, and to continue achieving 24kg of DM intake. Fortunately, high DM grass silage helped, with its 32% DM, 11.6M/kg of ME and 13.4% crude protein.

“We wanted to keep the ration at 40% and a high level of nutrients in that 24kg DM. With lower cereal prices, we increased wheat content to offer starch and match the protein going into the rumen with energy,” says Mr Allen. Rolled crimped wheat has been increased from 2.75kg to 3.25kg. Sugar beet pulp and protein blend rates were also increased by 0.25kg each.

Mr Clarke is now feeding 34 cow portions to a 32-cow group, so intakes are matching targets. “But we will continue to test the clamps regularly this winter to keep a close eye on quality, as we aim to achieve more milk from forage.”

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