An experiment utilizing finisher pigs was conducted to determine the effects of dietary manipulation on pig growth performance, nutrient excretion, gaseous emissions, and the mass balance of nutrients for an entire 94-d period. A total of 88 pigs [Duroc x (Yorkshire x Landrace)] initially weighing 32.1 kg was blocked by weight and allotted to two dietary treatments. Dietary treatments were randomly allotted to four rooms with 2 pens (11 pigs/pen) per room (22 pigs/room). Dietary treatments consisted of a fortified corn-soybean meal diet and a Reduced Excretion (REx) diet. The REx diet had a 3% units decrease in CP with Lys, Thr, Met, and Trp added as needed and a reduction in available phosphorus of 0.10% with phytase inclusion. Also, in the REx diet, monocalcium P replaced dicalcium P and CaCl replaced 50% of the limestone in the control diet. Furthermore, organic sources of Fe, Zn, and Cu replaced inorganic sources of these minerals in the control diet. Inclusion levels of the organic sources provided the same supplemental level of each trace mineral as that supplied by the inorganic sources in the control diet. All diets within phase were formulated on a SID lysine basis (0.92, 0.79, 0.65, and 0.56% for Phases 1 to 4). The dietary treatments were fed in four phases: 32 to 55 kg, 55 to 82 kg, 82 to 102 kg, and 102 to 113 kg. Feed was weighed before filling the feeders, and each room was equipped with a water meter to determine water disappearance.

Each week, the pigs were removed from each room and weighed. At this time, the feeders were weighed to calculate feed intake and a feed sample was collected from each feeder. Also, at this time, water disappearance was recorded, total pit volume was determined, and samples from the pit were obtained. The analyses of the feed and slurry samples were performed by the OSU Soil Testing Lab. Nutrient concentration of the slurry was multiplied by total pit volume to achieve total nutrient output per week, by dietary phase, and for the entire finishing period.
Airflow from each fan was continuously measured and ammonia and hydrogen sulfide concentrations in the exhaust air were measured. The generation and emission rates of each gas were calculated. The emission rates for Rooms 1 to 4 were based on the mean gas concentration in the exhaust air of each room and the total airflow rate for each sampling cycle.

When a room of pigs reached approximately 114 kg, 6 pigs from each room were transported to the university meat lab and humanely slaughtered. Following this, the whole pig was ground and a sample was taken to determine nutrient content of the pig. In addition, six pigs were slaughtered at the beginning of the test period to determine initial nutrient content. Following the end of the experiment, mass balance was calculated for N, P, and macro and micro-minerals by quantifying the total nutrients entering the room and the total nutrients exiting the room via the slurry and exhaust air. The calculations for intake minus output (slurry, exhaust air) were for the total growth period.

There were no effects of dietary treatment on ADG, ADFI, and F:G. However, the daily intake of N and P was reduced for pigs fed REx. There were no effects of treatment on carcass traits.

The predicted initial body composition of pigs entering the experiment was similar for both dietary treatments. The percentages and final weights of water, CP, fat, and ash were not affected by dietary treatment. Additionally, the whole body weights of N, the macro-minerals, and micro-minerals were similar for both dietary treatments.

Slurry volume and temperature were similar for pigs fed both dietary treatments. However, slurry pH was reduced for pigs fed the REx diet. Slurry from pigs fed the REx diet had lower concentrations of N, NH4-N, P, Ca, K, Mg, and Fe. The daily excretion of DM, N, P, Ca, K, Mg, S, and Fe were reduced for pigs fed the REx diet. The cumulative excretion of DM, N, and P for the entire finishing period was reduced by 2.3, 0.89, and 0.24 kg/pig, respectively, for pigs fed the REx diet.
Airflow was similar for all rooms. However, the concentration (mg/m3) of NH3 in the exhaust air was reduced by 47% for pigs fed the REx diet. The decrease in concentration for pigs fed the REx diet resulted in a 47% decrease in ammonia emitted per pig per day. However, the concentration, emission rate, and emission per pig for H2S were not affected by dietary treatment.

Calculation of the mass balance for other nutrients also was performed. Mass balance calculations revealed that a greater proportion of N, P, Ca, K, Mg, S, Fe, Zn, and Cu that entered the finisher exited via the market pig for those fed REx. These results suggest the dietary manipulations employed in this study markedly reduced nutrient excretion and shifted the proportion of nutrients exiting the finisher into the market pig. By increasing the proportion of nutrients leaving as a finished pig, a lower proportion of those nutrients is available to be released to the environment. This project was funded by the National Pork Checkoff.

Contact Information:
Scott D. Carter, Ph.D.
212B Animal Science
Oklahoma State University
Stillwater, OK 74078
Phone: 405-744-8869""
Email: [email protected]