Effects of dietary protein concentration (corn:soybean meal ratio) on the performance and carcass characteristics of growing boars, barrows, and gilts: mathematical descriptions.

Three split-plot trials using completely randomized whole-plot designs were conducted to determine the effect of dietary CP level (corn: soybean meal ratio) on daily feed intake, rate and efficiency of gain, and carcass characteristics of growing boars, barrows, and gilts. One hundred eighty-nine pigs were assigned to seven corn-soybean meal diets ranging from 11 to 23% CP in two-percentage-unit increments. The pigs were penned individually and had ad libitum access to feed and water. The average initial weight was 19 kg and the average final weight was 105 kg. Regression analysis revealed that maximal rates and efficiencies of gain were attained by all sexes when animals consumed diets that contained 17 to 19% CP. Average daily gain increased linearly as dietary lysine intake increased from 5 g/d to approximately 25 g/d. Carcass leanness increased at a greater rate for boars than for barrows and gilts (P < .05) as CP levels increased from 11 to 19% CP. The results indicated that both inadequate and excess dietary CP concentrations are detrimental to the rate and efficiency of gain and carcass quality of growing-finishing boars, barrows, and gilts. Interactions between sex and CP level indicated that inadequate CP concentrations were more detrimental to boars than to barrows and gilts.