31 May 2002

US tech nails fat trouble

By Richard Allison

SIMPLE on-farm technology developed in the US has helped identify the reasons for low milk butterfat on one Notts unit this summer.

Adrian Scholls 120-cow herd at Home Farm, near Colston Bassett, is experiencing below target milk fat percent. "Milk fat is 0.4% lower than previous years at about 3.5% during May," says Mr Scholl.

"Cows are being fed a ration with finely chopped maize silage as the sole forage. Grass silage has run out. Straw is included in the ration, but milk fat has remained low, while daily milk yields are more than 30 litres a cow."

The ration also contains Sodagrain, maize distillers, orange peel, Megalac, a soya, rapemeal and sugar beet pulp premix and minerals, he says.

In New York State and Pennsylvania, the reason for low milk fat is that most dairy rations are over processed, says Keenans US specialist Tony Hall. "Sub-clinical acidosis is endemic across farms in both states, even where mixed rations are fed."

When complete rations are over-mixed, they will not prevent poor rumen health and low milk fat. And rations which have the same chemical analysis can have differing effects on cow performance.

Mr Hall believes this is due to differences in the physical structure of cow rations.

"One test routinely used by US advisers to check whether it is a healthy ration for cows is the Penn State Separator, which consists of three plastic trays in a stack."

The top tray has holes 2cm (0.75in) in diameter to collect the rumen effective fibre. The second tray has 0.84cm (0.33in) holes and the bottom tray collects the fine, concentrate-like material.

At Home Farm, Mr Hall placed samples of maize silage on the top tray and after a series of shakes, the proportion of feed in each tray was measured (see table). "Despite maize silage containing more than 40% neutral detergent fibre (NDF), nearly half passed down to the bottom tray . The top tray was virtually devoid of good chewing material," says Mr Hall.

"When testing the whole ration, there was too much material passing into the bottom tray. This fraction acts like a concentrate and should account for less than half the ration to maintain rumen function."

This highlights that adding 1kg a cow of straw is not always the solution for low butterfats, particularly with over-chopped straw, which contains little top tray material. Options to reduce the fine material include adding more straw to increase the top tray proportion, but this may reduce energy intake and cow performance.

"Another solution is to increase the middle tray proportion by including additional orange peel or sugar beet pulp. Longer term, a marginal increase in maize chop length is desirable when feeding at high inclusion rates."

Mr Hall also examines dung from the cubicles to shed more light on ration structure, "The stiff consistency and lack of scouring suggests no real acidosis problems."

Dung was then washed in the colander with running water. "In classical sub-clinical acidosis dung consists of long fibres more than 0.5in long. But on this unit, fibres are shorter and some cracked grains are undigested suggesting the problem is feed not being broken down by microbes, not a lack of rumination," he says.

A lack of rumen soluble nitrogen could be the cause of inadequate fibre digestion and adding feed grade urea may increase the cows response to adding straw in the ration, says Mr Hall.

Adding urea would also increase digestion of maize grain. This is significant, as this ration contains 66% maize silage on a fresh weight basis, which equates to 10kg a day of moist fermentable grain. Dung also contained some undigested cracked grains, he says.

"Maize is an excellent feed, which can be successfully fed at high rates, but should be regarded as a semi-concentrate which is dependent on added structural fibre."

Based on the ration and dung assessment, Mr Hall believes more top/middle tray fibre and soluble protein would improve both milk yields and solids. &#42

Penn State Separator results

Maize Whole Ration

silage ration target

Top tray 0.5% 5% 4-10%

Middle tray 63% 41% 40-55%

Bottom tray 46.5% 54% < 50%