Greater reliance on the use of imported soya since the EU ban on mammalian proteins in livestock diets has resulted in an increased risk of nutritional variability in pig feeds, particularly when used for younger animals.
Dr Julian Wiseman, Professor of Animal Production at Nottingham University, points out that the use of whole soya beans or oil-extracted meal now accounts for over 50 per cent of EU protein equivalents in livestock diets. But plant proteins, particularly soya, are inherently less well digested than animal proteins.
Writing in "Technical Update" the electronic newsletter for the UK-based pig-breeding company ACMC, he says that since raw soya beans contain a number of anti-nutritional factors, it is essential they are heat-processed before being added to pig diets. But descriptions such as "cooked", or even naming the process itself, are of little value since each process has a wide range of operating conditions. While temperature is the most influential aspect of processing, humidity, time and particle size may also be changed, which increases the variability and ultimate nutritional value.
"The problems of ignoring this become greater when processed raw materials are used more frequently and at higher rates of inclusion. This is precisely what is happening with soya beans."
Trials have shown that trypsin inhibitors in full-fat soya beans, for instance, reduce the height of villi - the finger-like projections in the piglets' gut - subsequently reducing daily liveweight gain by over 300g, where trypsin inhibitors are high. Quality control within the feed industry is therefore of major importance. Although a number of nutritional tests can be carried out, Prof Wiseman's view is that in vivo tests are the only reliable means of assessing nutritive value.
