29 March 1996


Counting the number of category approvals that have been awarded under the UKASTA Forage Additive Scheme is not the way to choose this seasons forage additive. An independent nutrition consultant tells

Sue Rider why

SALESMEN and experts are misleading livestock producers by misusing the findings of the UKASTA Forage Additive Approval Scheme.

This is the warning of independent nutrition consultant Stuart Jones.

He advises producers to beware of reps and indeed advisers who recommend products simply by counting the number of category approvals that have been awarded under the scheme.

While Mr Jones welcomes the scheme as a step forward, he remains concerned at how it is being misused in practice.

"Used correctly it can help farmers select an appropriate additive for their particular needs," he says. "But too many clever people are trying to turn it into some sort of Which table of best buys which it neither is nor was intended to be."

The scheme requires only that a product improves a characteristic compared with a negative control. That is the treated silage is better than a silage made from the same crop in the same way at the same time but without additive.

It does not compare specifically the effectiveness of one additive with that of any other. "It is quite wrong to say that A is better than B," says Mr Jones. The UKASTA scheme does not provide any such evidence although other studies, notably those of the Kingshay Farming Trust, do, he maintains.

The number of category approvals is not an important factor, he maintains. But the efficacy to aid a specific objective is.

"To state the obvious a producer who, for whatever reason, wilts the crop to 30-35% dry matter before ensiling should not take too much notice of whether the additive reduces effluent production.

"But if the same producer intends to store that silage in a wide, out-of-doors clamp and feeds out with a bucket then they should be very interested in the additives ability to reduce aerobic spoilage after opening."

Where an additive has been shown to increase voluntary appetite and hence animal performance, Mr Jones poses another question: "How many farmers are really looking to increase intakes of silage?" He acknowledges that last summers drought has exaggerated the difficulty this winter, but stresses that in most years many producers fail to make sufficient silage to allow their cattle ad lib access.

Given that cows may eat 10kg of silage dry matter daily (24% dry matter silage), they take in 7.5t of fresh silage a head over a 180-day winter, Mr Jones estimates. "When an additive is used which increases voluntary appetites by 10%, the farm will need an extra 75t of silage for 100 cows."

Turning to inoculant additives he questions those experts who still promote the over simplistic view that the number of viable bacteria added a gram of crop is all important. This would be the case only if all strains of lactic acid bacteria (LAB) converted plant sugars into lactic acid with equal efficiency. The idea is convenient but far from the truth.

Some strains of LAB grow more quickly than others, he explains. For products which contain specially selected strains, doubling times (time taken for a LAB cell to grow and divide once) under laboratory conditions are usually 30-40 minutes. "Although in practice other factors will also be important, especially in the first few hours, it is reasonable to assume that if strain A is faster in the laboratory, it will be also in the silage clamp," he says.

In Fig 1 strain A was added at 1m colony forming units (cfu)/g of grass and has a doubling time of 40 minutes whereas strain B, which doubles every 30 minutes is added at only 500,000 cfu/g. Numbers of the two strains should be equal after only two hours, then strain B increases much more rapidly.

This example illustrates that it is not the number of cfu in the additive that is important but the rate at which these bacteria multiply and produce acid, says Mr Jones.

When any supplier cannot (or will not) give this information, perhaps its time to ask someone who can, he says.

He acknowledges that the scheme should require evidence from trials to support claims for effectiveness. But says that unfortunately there is a widely held understandable view that such a policy favours large companies with big research budgets. Whereas there is a requirement to achieve a minimum number of statistically significant results, the assessment panel will have no knowledge of trials carried out where the results were not significant, he points out. Nor, in its present form does the scheme provide information on the extent of any improvement achieved.

Mr Jones questions how many salesmen and advisors take time to explain to farmers the difference between trial results which are statistically significant and those which are relevant in practice.

As an example he examines the effect of two additives, X and Y, on the liveweight gain of cattle (see table) when compared with controls. For additive X, although the difference is very small, it is highly significant statistically and the trial would probably be accepted as meeting scheme needs. For additive Y, however, because there are some minuses as well as bigger positives (more variation) the results are not statistically significant. This is despite the average response being nearly four times greater than that for additive X. The trial would not be accepted.

On the other hand, if the numbers one to nine in the table represent separate trials, the company need submit only the "good" results for assessment and quite legitimately conceal the "bad" results. Clearly a large company which may commission 10-15 trials (at costs up to £35,000 a trial) is more likely to gain more "approvals" more quickly than the small ones which may be none the less innovative.

Some smaller companies have products on the market which have been approved only because they share the same active principle as an established product. These products may not have been tested in the form actually sold.

Equally important, he says, is the real concern that the high costs of the necessary research studies will stifle innovative product developed. "It is certainly true that some of the best products (for specified purposes) are not yet registered because the small companies which developed them cannot justify the cost of carrying out the number of trials required," he says.

For example, independent research in 1994 compared the efficacy of 10 commercially available additives to reduce aerobic spoilage in maize silage against a control (see bar chart). It is wrong to draw conclusions from only one experiment, he admits. But notes that only additives 3, 4, 5 and 7 carry category C2 approval (reduces aerobic spoilage). Additive 6 was the control, Additive 1 was developed by a small company working with a limited budget. It has, therefore, not been approved because the company has carried out only one trial to date.

The Way Ahead

Mr Jones says he is not criticising the UK scheme. But says there are areas which can be improved. His concern is that its value to the producer will be diminished unless everyone pays more attention to principles and less to counting "blobs" which may have no relevance to individual requirements.

For his part the producer should consider an additive only as an aid to achieving the objectives of a carefully planned and integrated conservation programme.

None will be an instant panacea to all possible problems but given truly independent advice many may help to improve standards still further. &#42

Trial to show effect of additives X and Y on cattle daily liveweight gain

Number ofDaily lwg (kg)

cattle withinAdditive XAdditive Y

trialless controlless control











If used correctly the category approvals introduced last November for the UKASTA Forage Additve Approval Scheme can aid additive selection.

Nutrition consultant Stuart Jones: Concerned at how the scheme is being misused in practice.

Many producers fail to make sufficient silage to allow ad lib access.