Effect of protein content of the diet on nitrogen excretion by pigs

Abstract

Five balance experiments were undertaken to investigate the reduction of nitrogen excretion enabled by the decrease of dietary crude protein content or the increase of essential amino acids content through substitution of protein rich feedstuffs and/or supplementation by some essential amino acids. Among different earlier experiments, dealing with the effect of a reduction of dietary crude protein on performance, five series of two diets were selected. Within each series the decrease of dietary crude protein content or the increase of essential amino acid content have led to similar or slightly better growth performance. Similar diets were fed to castrated males placed in metabolism crates during a 10-day period in order to measure urinary and fecal nitrogen excretion. Apparent fecal digestibility of nitrogen was similar within a trial. Nitrogen retention was also relatively constant within a trial and was related to physiological stage rather than to dietary crude protein. The decrease of dietary crude protein content down to 155 g/kg during the growing period and 135 g/kg during the finishing period enabled a reduction in urinary nitrogen excretion. Compared to current levels of 170 and 145 g/kg respectively, the difference in nitrogen excretion was in the range of 15 to 20% of the former crude protein content. The increase in essential amino acid content up to 9.6 g lysine/kg during the growing period and 8.6 g/kg during the finishing period did not modify daily nitrogen excretion of castrated males although this was probably not the case in the previous growth experiment completed with female pigs.