Swine diets have been optimized for pig performance, based on feed efficiency, average daily gain and days to market, but not the reduction of wasted nutrients excreted in manure.

The nitrogen and phosphorus in swine manure are becoming a political and regulatory focal point for the industry. Here are a combination of strategies from South Dakota State University swine nutritionist Hans Stein to maximize on both traditional feed efficiency and nutrient management.

In a typical feeding program, for every 100 g. of nitrogen (N) in the feed, 34 g. are utilized by the pig to grow bone and muscle and 66 g. are excreted in the manure. Similarly, for every 100 g. of phosphorus (P) in the feed, 40 g. are used by the pig and 60 g. are excreted.

Tallied over a year, a 500-sow, farrow-to-finish operation produces 55.9 tons of N and 11.4 tons of P in manure. Production of 2,500 head (1,000 head with 2.5 turns) of finished hogs produces 12.4 tons of N and 2.3 tons of P annually.

Sources of Waste

Stein finds that, on average, 5-8% of feed is wasted. “If 5% of the feed is wasted, that waste accounts for 7.5% of the total nutrients in the manure,” he says.

A portion of the waste comes from dry feed stuck to a pig's snout after it visits the feeder. If a pig places its head in the feeder and takes a mouthful of feed 60 times a day, but has to back out of the feeder to eat, as much as 1.5 g. of feed per mouthful can be wasted, Stein says. If the feeder is properly designed for the pig's requirements, the wasted feed falls back into the feeder; if not, as much as 90 g./day/pig, or 0.20 lb./day, is wasted.

“Feeders used must be the right design for the age group,” he stresses. “The design must allow the pig to raise his head inside the feeder, because if he backs out, more feed is wasted.”

What's Practical?

Stein expects that producers can reduce the N and P excreted in manure by about 40-50% by combining the following management strategies:

  1. Smaller particle size means better digestion of N, but there must be a balance, because of the potential for ulcers from fine feed. Stein recommends uniform particle size at 700 microns. Reducing the particle size from 900 to 700 microns would improve digestibility by 1-2% and reduce N excretion by 6-7%.

    “Uniform particle size is key,” he stresses. “You can set the grinder at 700 microns, but it's no good if the range is from 200 to 1,500.”

  2. Add phytase to all swine diets, including gestation and lactating sow diets. All diets must be formulated on digestible P basis.

    European research shows a 50% reduction in P when phytase is added to diets.

    “Phytase is a no-brainer,” Stein says. “It is cost-effective to spend the money on phytase, because it is balanced with savings on monocalcium phosphate.”

  3. Add more phases to grow/finish to meet dietary needs and eliminate the excretion of excess amino acids in manure and urine.

Stein suggests four nursery diets and five grow/finish diets.

“In the nursery, I recommend changing the diets every 7-10 days because the pigs' requirement changes very fast,” he says. “During the grow/finish period, diets should be changed every three to four weeks.”

Here are Stein's formulations for standardized ileal digestible lysine and digestible P levels for corn-soybean meal diets with no fat added:

Lysine P
Diet 1 1.35% 0.55%
Diet 2 1.20% 0.40%
Diet 3 1.01% 0.32%
Diet 4 0.95% 0.28%
Diet 5 0.85% 0.25%
Diet 6 0.75% 0.22%
Diet 7 0.65% 0.19%
Diet 8 0.55% 0.16%
Diet 9 0.50% 0.14%

“The more phases fed, the closer we get to the actual requirements of the pig,” he says. “If you give the pig what it needs, there will not be a difference in the carcass.”


Reducing wasted feed, making uniform feed at 700 microns, feeding phytase, and added phases can reduce the N excretions to 34.5 tons and 6.8 tons of P for the 500-sow farrow-to-finish farm. Similar reductions to 6.9 tons of N and 1.4 tons of P can be achieved for the 1,000 head finisher turned 2.5 times a year.