Feed Management as a Tool for Manure Nutrient Reduction 

Purchased feeds or feed ingredients create the major portion of livestock farm nutrients that, if not removed as animal products (meat, milk, eggs), manure, or effectively recycled as fertilizer for a cropping program, can result in a whole farm nutrient imbalance leading to problems such as water quality.

Several feed management practices however, can be used to reduce nutrient excretion by animals and potentially reduce manure nutrients by up to 40 percent. These might include precision feeding (phase feeding, splitsex or group feeding), feed processing, feed additives, feed resources, crude protein reduction with the addition of synthetic amino acids, reduction of dietary phosphorus to the amount actually needed by the animal, use of phytase, use of more highly digestible feed ingredients, i.e., sources of available P and N, and routine feed analyses and diet formulation.

Precision feeding is the practice of changing the level of available nutrients fed to the animal based on age and level of production. Decreasing dietary protein level as the animal matures and protein needs lessen decreases excess protein that would be eliminated in the manure.

Split sex or group feeding is the practice of feeding animals of the same type, sex, size, or production level similar diets or amounts. This eliminates a need to “over feed” for the production of animals that require higher nutrient levels. This over feeding is a source of many of the excess nutrients produced on animal operations.

Feed processing changes the form of the feed in some manner through grinding, steam flaking, pelleting, ensiling, or other methods which makes the nutrients of the various feedstuffs more available. The simple act of grinding grain increases surface area for enzyme digestion and the likelihood that the feed nutrients will be in the digestive tract a sufficient amount of time for absorption, whereas they might be expelled in the manure virtually unchanged if they were fed as whole grain. Ensiling, pelleting, and steam flaking can all increase the digestibility or absorbability of feed nutrients, decreasing the likelihood that they will be excreted.

Feed additives such as enzymes, agonists, or other growth promotants and amino acids can increase the digestibility or absorption of nutrients. Phytase is an enzyme that when added to feed, can increase the digestibility of organic phosphorus. Phytase application with a corresponding decrease in supplemental inorganic phosphorus has been shown to reduce manure phosphorus excretion by up to 40 percent in poultry and swine.

Feed resources are genetically enhanced grains, by-product feeds, new or alternative grains, and feedstuffs produced on the farm where the manure will be deposited. Feed resources that are new to the animal operation can be utilized to provide for the nutrient needs of the animal, and also decrease the nutrient output in the manure. New varieties of grain have been produced that contain a large percentage of available phosphorus. These grains can reduce manure phosphorus by as much as 40 percent in poultry and swine.

Feed management is one of the six core elements of the Comprehensive Nutrient Management Plan (CNMP). A conservation practice standard was adopted by NRCS in 2003, making feed management eligible for voluntary conservation financial assistance programs. In 2004, NRCS signed a Memorandum of Understanding with the American Registry of Professional Animal Scientists to certify technical service providers (TSPs) in the area of feed management. TSPs working in this area and certified by ARPAS as experts will be able to assist farmers in making feed management decisions and in developing the feed management element of the operation’s CNMP.
Your contact is Glenn Carpenter, National NRCS Animal Husbandry Leader, at 301-504-2208, or glenn.carpenter@usda.gov.