Researchers are finding cost-effective ways to reduce the nitrogen and phosphorous excreted in swine manure.

University researchers continue to search for the optimum balance between maximum pig performance, cost-effective finishing diets and growing environmental concerns.

An ongoing study conducted by Iowa State University at Kirkwood Community College, Cedar Rapids, IA, is incorporating phytase in diets. The enzyme increases dietary phosphorous available to finishing hogs and therefore reduces the amount of phosphorous excreted in manure.

The diets and housing are designed to mimic commercial production, says Larry McMullen, Iowa State University Extension swine field specialist, who is conducting the study. The Iowa Pork Industry Center funds the research.

In the study, groups of 100 crossbred pigs were assigned to two dietary treatments, with or without added phytase. The animals were housed 18/pen in a 100-head room of a 600-head, double-curtain sided, totally slotted facility. Pigs entered the study at about 115 lb. and exited at a 260- to 270-lb. slaughter weight.

The meal-form, corn-soybean meal diets are fed in four phases. Split-sex feeding is maintained. Control and test groups alternate between gilt and barrow groups. Crude protein is 18%, 15.5%, 14.2% and 12.5% in the four phases. Lysine was 1.08%, 0.91%, 0.82% and 0.70% in the four phases. Phytase units/lb. added to the test diet are at 150, 150, 144 and 125 units, respectively, for the four phases.

Editor's note: Phytase activity is expressed as phytase units (FTU)/unit of feed. For example, BASF's Natuphos 5000 contains a guaranteed minimum of 5,000 FTU/g. or 2,268,000 FTU/lb.

Liquid and solid manure samples were collected every two weeks. Testing was completed for percentage of moisture, solids, total nitrogen, phosphorous and potassium. Feed samples for each phase also were collected for analysis.

Preliminary Results Three of the four replications of the study are now complete. McMullen estimates the reduction in phosphorous excretions at approximately 15-20% for the phytase test group as compared to the control group of hogs.

While all of the data is not summarized, the first test group of barrows has an average daily gain of 2.01 lb./day from 118- to 270-lb. market weight. The control group of gilts had an average daily gain of 1.95 lb./day from 115 to 259 lb.

The reduction in phosphorous excretions will help producers manage manure in the future, McMullen says.

"If the state environmental agencies move to a requirement for phosphorous-based manure management plans, swine producers will have to use every method they can to reduce the phosphorous in order to increase the land base," he says.

Complete results, including analysis of the cost-effectiveness of the phytase-added diet, will be available spring 2001, McMullen says.

Reduced Protein Diet Animal scientists at Purdue University have developed a low-cost, reduced crude protein swine diet that reduces the nitrogen and odor produced by finishing hogs.

The diet includes 10% soybean hulls, while soybean meal and corn content are reduced. The cost of the diet is estimated at $3.86/ton less than the standard protein diet. A corn price of $2.25/bushel and soybean meal price of $180/ton are used to calculate costs of $100.54/ton (reduced crude protein) and $104.40/ton (standard crude protein) diet.

Purdue's research included four groups of 40 pigs. Average pig weight at the start of the test was 133 lb. In a nine-week experiment, all pigs were fed a corn-soybean meal diet (13.1% crude protein, 0.70% lysine) for the first three weeks. Then pigs were fed either a diet with 12.4% crude protein and 0.65% lysine or the low-protein diet with 9.7% crude protein, 0.65% lysine and supplemental amino acids of 0.372% lysine, 0.005% tryptophan and 0.042% threonine.

Pigs were weighed and feed consumption was recorded at zero, three, six and nine weeks. Aerial ammonia concentration and pit samples were taken at weeks three, six and nine. Pigs were scanned for backfat at the 10th rib with a real-time ultrasound machine at weeks three and nine.

The researchers found much variability between the four replications in the research (Table 1). Two of the replications showed similar ADG and average daily feed intake (ADFI) between the two diets. The ADG and ADFI were 1.74 lb. and 6.14 lb. for the standard crude protein and 1.68 lb. and 6.32 lb. for the reduced crude protein diet. Similarly, researchers found no significant difference in backfat at week nine (0.75 in. vs. 0.79 in.) for the two diets.

In the other two replications, pigs fed the standard crude protein diet had an ADG of 1.95 lb., compared to 1.62 lb. for the reduced crude protein diet. ADFI ranged from 6.49 lb. to 6.10 lb. for the standard and reduced crude protein diets.

Researchers note that the pigs, especially gilts, did not consume enough feed to compensate for the soybean hulls in the diet.

More research on reduced crude protein diets is necessary, says Brian Richert, animal scientist at Purdue.

Researchers completed follow-up trials and found that today's genetically lean pigs cannot increase their intake as much as hogs from the early '80s, Richert says. "So, a high-fiber diet results in reduced net energy intake and growth performance," he explains.

Richert points to other Purdue trials that reduced crude protein in a corn-soybean diet by 3.5-4% but did not reduce growth performance. Further reductions in crude protein cause isoleucine and valine amino acid deficiencies, especially in the gilts, he says.

Research Results Data (Table 2) show a 41% reduction - 21.3 versus 12.5 parts per million (ppm) - in the aerial ammonia concentration in rooms where pigs were fed the reduced crude protein diet. Hydrogen sulfide was reduced from 0.34 ppm (standard crude protein diet) to 0.25 ppm for the reduced crude protein diet. Samples taken from the manure pit showed a 15% reduction of total nitrogen from 2,571 ppm for the standard diet to 2,177 ppm for the reduced crude protein diet. Manure generation was reduced by 15%, and total manure nitrogen was reduced by 25% (Table 3).