PHOTO: Rachael Brugger
Susan Kerr, DVM
January 22, 2015

This will come as no surprise: Pigs can be smelly! We humans find the excrement of most monogastrics, including pigs, dogs, cats and primates, offensive to our senses. Hundreds of compounds combine to create the symphony of smells we recognize as hog manure. Bacteria in pigs’ intestines and their environment break down the manure, releasing hydrogen sulfide, ammonia and methane—all of which are pretty stinky. There are two major ways to combat this: feed changes and housing-management strategies.

Feed Management

A supplement called PROMAX, which contains lactobacillus (a probiotic), enzymes and yeast cultures, has been shown to reduce air ammonia levels between 5 and 40 percent. On a more practical basis, feeding only the exact amount of crude protein a pig requires at various stages of growth, pregnancy, lactation and maintenance helps reduce excess nitrogen excretion and ammonia production. Feeding trial results revealed that if crude protein is reduced by 3 percent and replaced with synthetic essential amino acids—primarily lysine—both nitrogen excretion and ammonia levels dropped significantly. The takeaway here is to use phase feeding—a specific ration appropriate for the nutritional needs of growing pigs at various stages of development—which also reduces feed costs and nutrient waste while increasing feed efficiency.

Other research-based, feed recommendations include adding fiber to the diet; pelleting or grinding feed to increase digestibility; wet-feeding to reduce feed and water spills; providing water low in nitrates and sulfates; feeding only the minimum required levels of sulfur-containing amino acids, such as cysteine and methionine; controlling dust by adding fat or oil to the ration (dust particles carry swine odors); and adding the enzyme phytase to rations so pigs can digest phosphorus sources more effectively and release less hydrogen-sulfide gas as a by-product.

Housing Management

The most important factor in keeping both pigs and farmers happy is the same as it is with other real estate: location, location, location. Site the pig-raising area properly to minimize human contact with offensive odors. Determine the direction of prevailing winds, and locate the animal area downwind, provided this doesn’t negatively affect your neighbors. Slope animal areas by about 5 percent to promote drainage and drying; southern or southeastern exposures are best. Divert and/or collect runoff and rainwater to keep animal areas drier and help control smell. Screening or concealing hog pens from neighbors will likely result in fewer outside complaints, too.

Large outdoor dry lots can hold a lot of odor, so minimize their size as much as you can. Moving pigs through forage paddocks helps contain odors and distribute manure fertilizer, as long as pigs rotate paddocks frequently and you’re able to manage them on pasture.

You can use pigs’ innate intelligence and desire to stay clean by encouraging their natural tendency to defecate away from their sleeping area. Provide a comfortable and well-bedded area for sleeping, another area for feed and water, and enough room so they can establish a “back corner” for defecation. This will also make your task of removing manure much easier. You can compost it, bury it, or otherwise dispose of it in a manner and location that prevents offensive odors from bothering anyone. You can experiment with putting down activated charcoal in the defecation area of the pen and covering it with some sawdust or dirt—it might absorb odors until you can clean the area. If you can’t promptly remove the manure, covering it with straw will help confine the odors.

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