Amino acid and energy interrelationships in pigs weighing 20 to 50 kilograms: II. Rate and efficiency of protein and fat deposition.

Two experiments were conducted to investigate the relationships between amino acids and DE for pigs weighhg 20 to 50 kg. In Exp. 1, there were three dietary lysine levels that were either adjusted (1.50, 2.35 and 3.20 g/Mcal DE) for five DE levels (3.00 to 4.00 Mcal/kg) or unadjusted (.45, .71 and .%% of the diet) for three DE levels (3.50 to 4.00 Mcal/kg). In Exp. 2, diets containing six 1ysine:DE ratios (1.90 to 3.90 g/Mcal) at two DE levels (3.25 and 3.75 Mcal/kg) were fed. Pigs were housed individuiiy, and could eat and drink ad libitum. When pigs weighed 50 kg, their empty body composition was determined by the urea dilution technique in Exp. 1 and by prediction equations based on backfat in Exp. 2. For the adjusted diets in Exp. 1, protein deposition and protein depositi0n:DE intake increased (P < .01) slightly as DE levels increased. These criteria decreased linearly (P < .001), and fat deposition increased (P = .11) as DE increased when 1ysine:DE ratios were not maintained. As lysine levels increased, protein deposition and protein deposition: DE intake increased (P < .001) in both the adjusted and unadjusted diets. In Exp. 2, there was no effect of DE on either the rate or efficiency of protein deposition. Both protein deposition and protein deposition:DE intake increased (P < .001) and fat deposition decreased as 1ysine:DE ratios increased up to 3.00 g lysine/Mcal DE. Protein deposition: lysine intake decreased (P < .01) progressively as the 1ysine:DE ratio increased. Regression analyses indicated that protein deposition increased up to 3.00 g 1ysineMcal DE. The results demonstrate the need to adjust lysine according to energy levels and indicate that the optimum ratio for protein deposition was approximately 3.00 g lysine/Mcal DE (or 49 g of balanced protein/Mcal DE).