21 November 1997


The Forage Additive Approval Scheme helps producers select additives that have been

shown to improve particular aspects of forage conservation. But FAAS, as it stands, gives

no guidance on the likely economic benefit of any such improvements. Stuart Jones,

independent nutrition consultant, suggests a simple refinement which should help farmers

choose additives that are both technically efficient and cost effective

WHEN using the Forage Additive Approvals Scheme livestock producers can check that approvals granted to a particular additive are relevant to their own circumstances.

As an example, for a producer who consistently makes high dry matter silage, an additive that is approved as reducing aerobic spoilage (Category C2) would be more useful than one that helps to control effluent production. After some early teething troubles this aspect of the scheme now seems to be understood quite well.

However, the difficulty of whether differences in animal performance are of economic value remains. In its simplest form, if an additive was always associated with an improvement of, for example 0.05kg liveweight gain or 0.1kg milk yield an animal a day, then this would be statistically significant – and approval would be expected – but it may be of little practical importance. The value of the increase in animal performance might well be less than the cost of applying the additive.

It is, of course, necessary to avoid undue proliferation of categories but it might be possible to introduce a "tick" where trial results indicate, for example, that the value of the improvement is worth at least 2.5 times the cost of the additive used.

This is illustrated by the results of a feeding trial which was carried out at Graham Clays farm, Stone, Staffs, last winter.

Some 5ha (12 acres) of primary growth tetraploid Italian ryegrass mixtures were mown in the evening of May 16, 1996 and wilted for 18 hours in dry but overcast conditions. As the grass was picked up, alternative loads were treated with a new activated inoculant (see p20) additive, and ensiled in separate outdoor 50t clamps. The silages were evaluated at ADAS Wolverhampton.

Date of housing

Then 34 young bulls (Friesian, Blonde dAquitaine, Limousin and crosses) were housed on Oct 17 and offered silage ad lib. They were weighed on the Oct 24 and 25 before being allocated according to breed and liveweight to one of six pens (four of six and two of five animals). Bulls were offered either additive-treated or control silages ad lib – each supplemented with 2kg/head daily of an 18% protein compound. They were weighed again on Nov 21 and Dec 19 and 20.

The mean liveweight gains of the bulls offered the treated and control silages were both very satisfactory at 1.13kg +/- 0.18kg and 0.97kg +/- 0.24kg/head a day respectively over the 56 days.

Further detailed analysis confirmed that the additive had a significant effect on the daily liveweight gain of the bulls. Results from this trial met the requirements for Category A1 approval but what about the economics?

The straightforward interpretation (see table) is that the extra outlay of £2.17 gave a benefit of £9. Since the farmer takes the bulls through to about 550kg liveweight it is tempting to extrapolate the data to something like a 250 to 300-day period when the advantage to the bulls fed the additive-treated silage would be expected to be about £45 to £50 an animal. Alternatively it may be suggested that they will finish more quickly than those fed the control silage. Finally, the difference in voluntary intakes (and hence liveweight gain) may have been greater had the bulls not been offered supplementary concentrates.

The trial suggests economic advantage may be expected by using the additive compared with not doing so.

As such, livestock producers may well value the additional guidance and a tick after the category approval listing may be the easiest way of providing this. &#42

A simple refinement to the UKASTA Forage Additive Scheme would help farmers choose additives that are

cost effective.

Stuart Jones… the value of the increase in animal performance might well be less than the cost of applying the additive.

Effect of the silage inoculant additive X on the liveweight gains and silage intakes of young bulls

Group AGroup B


Final Liveweight (kg)262272

Initial Liveweight (kg)208209

LWG (kg/56 days)5463

Value of LWG (£)5463

Silage Eaten (kg/56 days)9631039

Cost of silage (£/t)1516

Cost of silage eaten (£)14.4516.62

Value of LWG

less cost of silage (£)39.5546.38

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