Effects of increased dietary lysine (protein) level on performance and carcass characteristics of growing-finishing pigs reared in a hot, humid environment

A study was conducted to evaluate the effects of rearing environment/season (hot, humid/summer vs thermoneutral/fall) and dietary lysine level (at or above current NRC recommendations) on performance and carcass lean content of growing-finishing pigs. Two trials, each involving 90 crossbred pigs, were conducted-one during the summer and the other during the fall-early winter. The trials were conducted in Northwest Florida (31 degrees N). Average daily low and high temperatures, and average relative humidities, respectively, were: 21 degrees C, 32 degrees C, and 81 % for summer; and 8 degrees C, 21 degrees C, and 84% for fall. Ten pigs (five males, five females) were allotted to a pen and each pen was assigned to one of three dietary lysine level treatments (0.75% grower/0.6% finisher, 0.85%/0.7% or 0.95%/0.8%) within each of three replicates. Corn-soybean meal-based grower diets were fed from 29 to 58 kg average body weight and finisher diets from 58 to 112 kg. The desired dietary lysine levels were obtained by altering the levels of corn and soybean meal. Pigs were housed in a curtain-sided building in pens with solid concrete floors that had an open water waste flush gutter across the rear 20% of the pen. Floor space per pig was 0.72 m(2). Over the entire growing-finishing phases, pigs reared during the summer grew 11% slower (P < 0.01), required 5% more (P < 0.03) feed per unit of gain and had 14% lower (P < 0.01) estimated lean gain per day than pigs reared during the fall. Performance and daily lean gain were not influenced (P > 0.10) by dietary lysine (protein) content for pigs reared in either environment. A hot, humid summer rearing environment had an adverse effect on growing-finishing pig performance and increasing the dietary lysine had no effect.