Self-selection of diets and lysine requirements of growing-finishing swine

A growth trial using 240 growing-finishing pigs (22 to 109 kg) was conducted to determine whether pigs offered a choice of low- and high-lysine sorghum-soybean meal diets can select the correct proportion of each to optimize performance and carcass leanness. Pigs on the choice treatments could select from two diets offered simultaneously in identical feeders. In two of the choice treatments, pigs had access only to the low-lysine diet for the first 2 d of each 21-d period to determine whether forced adaptation to the low-lysine diet would alter the proportion of diets selected. These were termed the adjusted treatments. The choice treatments were 1) .50 or 1.10% lysine, 2) .50 or 1.60% lysine, 3) same as 1 but adjusted, and 4) same as 2 but adjusted. Five additional treatments were arranged as a titration study to determine the lysine requirement of the pigs. The dietary lysine levels needed in sorghum-soybean meal diets to optimize performance and carcass leanness of barrows and gilts were .95, .80, and .70% lysine for the 22 to 52, 52 to 78, and 78 to 109 kg weight intervals, respectively. Lysine intake of pigs on the choice treatments exceeded the amounts needed to maximize performance and carcass leanness. The adjustment practice lowered lysine intake, but intake was still excessive. Percentage of lean and gain/feed were less desirable for the choice treatments than for pigs fed the .95-.80-.70% lysine treatment. These reductions, plus the higher lysine intakes, indicate that the choice treatments used in this research are not feasible for commercial swine production.