In the UK, farm animal effluents have been identified as a major potential source of nitrate pollution of the water system and it would be beneficial if nitrogen excretion from animals could be kept to a minimum. Recent work (Kay and Lee, 1995 and Lee et al., 1995), has shown that nitrogen excretion by pigs can be reduced by approximately 40 per cent by supplying amino acids in the diet in better agreement with the pigs requirement than currently available commercial diets. However, such diets will only be acceptable to the pig industry if they also maintain pig performance.

One hundred and ninety two pigs housed in 16 groups of 12 were given either a commercially available diet (G-com) or a diet (G-lc) low in crude protein (CP) during the growing phase (35-55kg). During the finishing phase (65-90kg), these pigs were then given either a commercially available diet (F-com) or a low CP diet (F-lc).