Aerial ammonia concentrations in the finishing room as well as at the exhaust fan were cut in half by feeding a high-available-phosphorous corn, reduced-crude-protein phytase diet, according to research at Purdue and Iowa State universities.

The first experiment involved 80 pigs weighing 177 pounds placed in two environmentally controlled rooms. Diets consisted of either a control diet of corn/soybean meal, or a reduced-crude-protein diet with supplemental synthetic amino acids formulated with high-available-phosphorous corn, 300 PU/ kg of phytase, 5 percent soybean hulls and a nonsulfate, trace-mineral premix.

Aerial ammonia concentration, hydrogen sulfide and detection threshold of odor samples were taken at weeks four and six from the room and exhaust air. Manure samples were collected during the first, third and sixth weeks.

In the second experiment, barrows were fed the same diet as in the first experiment, but gilts were fed a specially formulated control and reduced-protein phytase diet. A total of 100 pigs were tested, with five pigs per pen. The testing methods were identical to the first experiment. Data from both experiments were pooled.

Pigs fed the control diets in the first experiment had greater average daily gain, a higher gain-to-feed ratio, greater loin depth and less backfat accretion by week six. In contrast, the pigs fed the control diets in the second experiment had similar growth performance and carcass characteristics as the reduced- crude-protein diet.

By week six, the pigs fed the reduced-crude-protein diet had a 48.7 percent reduction in aerial ammonia concentration from room air and 49.8 percent reduction in aerial ammonia concentration in exhaust air. Hydrogen sulfide levels were 43.3 percent lower and the detection threshold of odor was 38.6 percent lower.