Present experiment aimed to examine the effects of low digestible crude protein (4% below the Japanese feeding standard) feed supplemented with amino acids on the growth and digestibility for growing pigs (30-70kg) and fattening pigs (70-110kg). Eight pigs (cross-bred) were used in this study and were divided into two groups each with the same mean body weight. Feed was prepared under the following condition; Standard feed including digestible crude protein (DCP) at 12.5% and 10.5% for the growing and fattening period, respectively and low DCP feed supplemented with amino acids (lysine, methionine, tryptophan, threonine and isoleucine) including DCP at 8.5% and 6.5%, respectively. They included even of total digestible nutrients. Feed intake, water drinking, feces and urea were determined everyday. Body weight and body size were determined every week. Digestion trial was conducted at body weight 50kg and 90kg. The loin area and backfat thickness at the starting point, finishing point for pre-fattening (70kg) and finishing point for fattening (110kg) were determined using ultrasonic measurement. The body weight gain, feed efficiency and gain of body size were calculated with the above mentioned values.
The results of the digestion trial showed that DCP was reduced up to 2.9% in the growing period and up to 3.8% in the fattening period, and crude protein was reduced up to 4.8% in the two periods. There was no significant difference for the daily gain and body size measurement between the standard feed group and low DCP feed supplemented with amino acids group over the total experimental period. These results supported that pigs require each amino acid which compose the protein, but not the protein itself. There was no difference in feed intake during pre-fattening period, but feed intake for the standard feed group tended to be higher than that in the low DCP feed supplemented with amino acids group during fattening period. The backfat, fat of top of ham and abdominal fat thickness in low DCP feed supplemented with amino acids group were larger than that of standard feed group. This result due to the surplus energy, which was caused by the energy supply and low activity of protein metabolism by low DCP supply.

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