PRESENT LIMITS OF PROTEIN SPARING BY AMINO-ACID SUPPLEMENTATION OF PRACTICAL CARP AND TILAPIA FEEDS

Protein, contributed by soybean meal in 30% protein feeds for carp and tilapia, was replaced in steps of 5% by 0.5% lysine-HCl and feed grains. Two experiments, one of 48 days and one of 58 were performed in experimental ponds of 200 m2 with 200 Israeli carp per pond, 260 g and 425 g initial weight, respectively. Five feeds of 3,900 kcal/kg gross energy were compared, each with 4 replicates: A. 30% protein/1.8% total lysine; B. 25% protein+0.5% lysine-HCl/1.8 total lysine; C. 25% protein/1.4% total lysine; D. 20% protein + 1.0% lysine-HCl/1.8 total lysine; E. 20% protein + 0.5% lysine-HCl/1.4% total lysine; All ponds in the same experiment received equal daily rations. In both experiments group B attained weight gains equal to group A, whereas groups C, D and E lagged 10% or more (p<5%). Non-retained protein/kg gain was 20% less than in group A and 10% less than in group C. Groups D and E were similar to B. In conclusion, 5% of the soybean meal in a 30% protein carp feed could be replaced by 0.5% lysine-HCl and 4.5% grains without impairing growth and resulting in 20% less nitrogen excretion. Further reduction of feed protein to 20% impaired weight gains, in spite of proper lysine supplementation. Tilapia were grown in the same ponds in two experiments lasting 57 and 51 days, 300 fish of 80 g per pond in the first, 250 fish of 190 g in the second. Four feeds were tested with 4 replicates: A. 30% protein/1.75% total lysine; B. 30% protein+0.5% lysine-HCl/2.1% total lysine; C. 25% protein/1.4% total lysine; D. 25% protein + 0.5% lysine-HCl/1.75% total lysine. The weight gains of both 30% groups (A and B) surpassed those of the two 25% groups (C and D) in both experiments (p<5%). The supplemental lysine did not yield any growth response at either protein level and thus failed to reduce nitrogen excretion.