Serving Society through Food Animal Agriculture

January 2001


Effects of Diet and Feeding Management on Nutrient Contents of Manure*




The development and implementation of comprehensive nutrient management plans (CNMP) for livestock and poultry operations is an approach to evaluate, adjust, properly utilize and possibly reduce the excretion of potentially environmentally damaging nutrients within the operation. Proper management of the diets of farm animals can be a valuable tool for reducing nutrient excretion , thereby significantly reducing potentially negative impacts on the environment. One component of the CNMP is feed management. In this fact sheet, a summary of basic principles on nutrition and feed management, and potential adjustments that can be made for livestock operations to minimize nutrient excretions is described. Additional fact sheets will provide specific feed management and nutrient excretion information for beef, dairy, poultry and swine. These fact sheets are not intended to be all inclusive. Therefore, consult with Extension personnel or certified animal nutritionists for detailed information and thorough evaluations of the animal diets and feeding management programs with a livestock and poultry operation.


Digestive Processes


The digestion, retention and excretion of nutrients in animal production is complex and can be significantly influenced by many factors. The initial digestive process involves the intake of feed ingredients provided to meet the requirements of the animals involved. First of all, the maintenance requirements of the animal must be met. Even at a maintenance level, there are always some endogenous losses of cell walls, recycled nutrients and enzymes, etc. In addition to the maintenance requirements, nutrients must be provided to meet growth and production requirements. These requirements are affected by stage of growth and the type of production (e.g. meat, milk, eggs,.) involved. How well the animal can assimilate (retain) nutrients for productive purposes, i.e., lean tissue, milk, eggs, depends upon the bioavailability of the nutrients in the diet, absorption, metabolism and retention. Ultimately, bioavailability affects the level of nutrient excretion. The amount of nutrients excreted by animals is affected by three main factors: (1) the amount of dietary nutrients consumed, (2) the efficiency with which they are utilized by the animal for growth and other functions, and (3) the amount of endogenous secretions. In other words, the amount of excreted nutrients can be expressed as:


Nutrients excreted = Nutrient intake - Nutrients utilized + Nutrients from endogenous sources

Generally, little can be done to influence the amount of endogenous losses per animal. However, by improving production rates, fewer animals are needed for a given level of productivity which dilutes these maintenance requirements. The primary way to reduce the amount of nutrients excreted by animals is to decrease the amount consumed and increase the efficiency of utilization of the dietary nutrients . The goal of efficient and productive feeding of animals, within economic and environmental constraints is to provide essential available nutrients for maintenance and production with minimal excess amounts.

Balancing the needed available nutrients from diverse feed ingredients is challenging. Nutrients in feeds can vary considerably and not all nutrients in feeds are available to the animal. Therefore, any means of increasing the digestibility or availability of nutrients will increase the potential for animal use and retention and reduce the amount of the nutrients excreted. There is increasing interest today in using enzymes, genetically modified feed ingredients and feed processing technologies to enhance the availability of nutrients to meet the needs of specific animals and reduce excretion of nutrients. In addition, a routine feed analysis program is imperative to formulate diets and adjust to maintain reduced nutrient excretions.


Ruminants and non-ruminants have different digestive systems. Because the ruminant (beef cattle, sheep and dairy cattle) has a large stomach compartment with indigenous microorganisms present, it is capable of digesting and utilizing nutrients and energy from forages, as well as, from the easily digestible grains (concentrates). The non-ruminant (monogastric) animal, which include swine and poultry, can not effectively use a large amount of forages (fiber), therefore, they must be fed diets with highly available nutrients. The volumes and nutrient composition of manure between and within species can vary tremendously due to species type and purpose, and composition of the diet.

Following are some factors that need to be considered before making adjustments (reduction) in the anticipated excretion of nutrients. In all cases, nutrients should be managed to meet the needs of the animals while minimizing excesses.

Feeding Management Factors


Grouping -- placing animals together of similar ages, weights and/or production levels


Gender -- placing animals of the same gender together


Climate adjusting the diet to meet specific climate conditions, i.e., temperatures, precipitation, or adjusting the building climate to optimize nutrient utilization


Feeding program using a multi-phase feeding versus minimal phase feeding; dividing the growth period into several periods with a smaller spread in body weight allows producers to provide diets that more closely meet the animal's nutrient requirements


Wastage minimizing the spillage of feed and water


Feed processing -- pelleting, extrusion, steaming, micronization, and reducing particle size increases digestibility of diets for pigs and poultry; not as critical for ruminants but some processes can improve digestibility


Diet Manipulation Factors


Available nutrients -- knowing the availability of nutrients in feed ingredients and formulating diets on an available nutrient basis


Nutrient levels some nutrients may be excessive in commercial animal diets; chemical analyses of ingredients and reformulation is critical to minimize excesses, however nutrient reductions can only be achieved until they are no longer economically feasible.


Genetics -- knowing the genetic capability of the animals, including feed intakes and responses, to environmental conditions is important to developing appropriate diets


Feed efficiency using antibiotics and other growth promoters will increase feed efficiency thereby reducing nutrient excretion


Specialty feed ingredients -- providing specific feed ingredients (e.g. high oil corn, nutrient dense corn, highly available P corn and soybeans, phytase enzyme ) helps achieve a proper balance or increase availability of nutrients.


Water supplies source of water can make a significant contribution to mineral intakes


Refer to additional fact sheets for detailed information for beef, dairy, poultry and swine. Also, contact your state Cooperative Extension Service or certified nutritionist for more detailed information.



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Prepared by the FASS Environment, Waste Management and Ecosystems Committee.