19 November 1999


INCREASING interest in home-grown proteins isnt just for grain; more producers are considering growing protein forage crops. However, additive choice for these crops can be more complicated that it initially appears.

According to Raymond Jones, silage specialist at the Institute of Grassland and Environmental Research, Aberystwyth, most ensiled protein crops are best treated with an inoculant additive to compensate for low sugar and reduce pH.

And although these crops are low in sugar, compensating for this by adding molasses is of little value, he warns.

These conclusions come from part of the institutes Milk Development Council-funded research on forage protein crops. As part of this, lucerne, red clover, peas and lupins have been ensiled in big bales using inoculants, providing varied results, says Dr Jones.

"Ensiling lucerne without an inoculant means the pH remains at six and it hardly ferments."

But a biological additive brings pH of lucerne silage down to 4.7. Using molasses alone as an additive had no benefit, although it improved fermentation slightly when used with an inoculant, he adds.

Results for red clover silage were similar. "It naturally has no bacteria, so a biological inoculant is crucial for a good fermentation."

Red clover is also low in sugar, at 5.9% in the dry matter. Even grass silage would be difficult to ensile if its sugar level was that low, he says.

But adding molasses alone to red clover, at 45 litres/t (10gal), failed to improve fermentation. And when it was added with inoculant the results were no better than when inoculant was used alone, says Dr Jones.

However, treating both lucerne and red clover with inoculant produced additional benefits: Nearly 30% reduction in free amino acids in both crops, so more protein remains available for use by the animal.

When red clover is treated with inoculant an extra 15% of microbial protein is generated in a cows rumen. Thats because an untreated silage has a microbial N content of 8g/kg, whereas one treated with inoculant has 9.5g/kg.

Inoculants also proved to be beneficial when treating forage peas, reducing pH from four to 3.7, while also having a positive effect on ammonia N concentration. The forage peas used in the trial were grown alone, making optimum harvest more predictable and the crop easier to ensile, adds Dr Jones.

Lupins, too, require an inoculant for good fermentation, but the greatest difficulty when ensiling lupins is that it is prone to lodging in wet weather. However, despite low yields, lupins produce a 31% crude protein crop high in by-pass protein, similar to soya and better than rapeseed, he explains.

He admits researchers have yet to discover why inoculants are beneficial to these protein crops and why molasses isnt. Molasses is high in sugar which in theory should benefit fermentation in these low sugar protein crops, he adds. &#42


&#8226 Inoculants beneficial.

&#8226 Molasses no benefit.

&#8226 More research required.

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