Amino acid and energy interrelationships in pigs weighing 20 to 50 kilograms. I, Rate and efficiency of weight gain

The relationships between dietary amino acids and DE for pigs weighing 20 to 50 kg were investigated in two experiments. In Fzp. 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, the effects of six 1ysine:DE ratios (1.90 to 3.90 g/Mcal) at two DE levels (3.25 and 3.75 Mcavkg) were investigated. In both experiments, diets were formulated using a constant ratio of com and soybean meal. Pigs (equal numbers of barrows and gilts) were housed and fed individually and had ad libitum access to feed and water. Digestible energy intake was not affected by energy content of the diets. In Exp. 1, lysine intake did not differ with DE in the adjusted diets but decreased (P c .001) as DE increased in the unadjusted diets. Weight gain was relatively consistent and gain:DE intake increased (P .05) on gakDE intake as DE increased. Both weight gain and gain:DE intake increased (P < .001) and backfat decreased (P c .01) as 1ysine:DE ratios increased. The results demonstrate the need to increase dietary amino acid levels in concert with increases in energy contents. Regression analyses indicated that weight gain and gain:DE intake for 20- to 50-kg pigs were maximized at approximately 3.0 g lysine/Mcal DE (or 49 g of balanced protein/Mcal DE).