Managing Nutrients in Poultry Diets
The increasing concern about animal agriculture’s impact on the environment requires producers to pay more attention to nutrient management. The key nutrients are nitrogen and phosphorus.
The protein and amino acids included in poultry diets contain nitrogen. The volatization of nitrogen results in the release of ammonia into the air and nitrates that can contaminate water sources.
Phosphorus is a major nutrient required for proper bone growth and is a component of cell membranes in the animal. Excessive phosphorus can negatively affect the environment by causing excessive plant growth in bodies of water. Producers have a vested interest in ensuring that nutrients are properly managed in their poultry operations to minimize environmental impacts.
Nutrient conservation can be achieved by increasing the accuracy of feed formulation, improving digestibility of diets and decreasing feed waste.
Producers can improve nutrient management by evaluating feed formulation accuracy. In poultry diets, evaluating species nutrient requirements and phase feeding can be used to minimize excessive nutrient output. Typically, the Poultry National Research Council (NRC, 1994) nutrient guidelines result in overfeeding nutrients. Excess nutrients are excreted. The nutrients that are lost reduce producers’ profits. Lemme (2007) stated that the energy and protein components of diets have the highest cost, so feeding excessive nutrients—especially protein—increases production costs. Poultry diets have traditionally been formulated on the basis of crude protein levels. The ideal protein concept allows the diet to be formulated on the basis of the digestible amino acid requirement of the bird (Lemme, 2007). This concept reduces nitrogen excretion because the amino acid profile of the diet more closely resembles the profile needed by the bird.
Poultry diet formulation needs to consider the species, age and sex of the birds. The diet composition for a broiler chicken is for rapid growth; a laying hen needs a different nutrient profile for egg production. Though the broiler and the laying hen could be fed each other’s diet, this would not achieve maximum efficiency of production and would waste nutrients. Poultry should be raised in single-age groups. For a mixed-age group, a producer will have trouble finding a diet with the necessary nutrients for proper growth of all the birds. As a result, mixed-age groups tend to be overfed nutrients. Again, the result is increased cost to the producer and increased nutrients excreted into the litter.
Differences in nutritional needs among sexes is another consideration. Split-sex feeding is not typical in the poultry industry but is worth considering.
Diets that are not completely digested by poultry are passed through the gastrointestinal tract and excreted into the litter. The result is loss of nutrients and money. Improving the digestibility of the diet will improve nutrient utilization by the bird. Ferket et al. (2002) reviewed the literature and suggested several ways to increase diet digestibility. The processing of feed, by milling and heating, can have both positive and negative effects on digestibility. Milling the diet or components of the diet decreases particle size and increases surface area exposed to enzymes during digestion. Particle size can be too fine, however. Then it causes irritation to the gastrointestinal system, which decreases nutrient absorption. Heat processing can gelatinize starches, break chemical bonds and deactivate antinutritional factors in feedstuffs. Too much heat, however, can form indigestible complexes and make fewer nutrients available for digestion or absorption by the animal.
Another way to improve feed formulation is to use enzymes such as phytase when formulating diets. Enzymes are proteins responsible for catalyzing a reaction without being consumed and are substrate specific (Applegate and Angel, 2004). Phytase is responsible for liberating phosphorus from the phytin molecule found in plants. Using phytase makes it possible to feed lower levels of inorganic phosphorus and reduce phosphorus excreted into the litter. Applegate and Angel (2004) report that supplementing a control diet with fungal phytase increased phosphorus retention by 10 percent. Therefore, the use of phytase and other enzymes can increase nutrient utilization by the animal.
Producers can improve diet digestibility by including feed additives such as prebiotics, amino acids, inorganic phosphorus sources, organic and inorganic mineral supplements, and highly digestible protein sources. All of these additives can increase digestibility and absorption of nutrients while minimizing nutrient wastage.
A major loss of nutrients—and an area where nutrient waste can be minimized—is feed management. Ferket et al. (2002) reported that a 1 percent increase in feed waste creates a 1.5 percent increase in litter nitrogen and phosphorus. Wasting feed can be avoided by ensuring that feeders are adjusted to the proper height, are not overfilled and are well-designed. Feed should be delivered to poultry in a form to reduce wastage and improve digestion. Pelletizing feed increases the efficiency of nutrient utilization, but poor pellet quality may cause gut motility and health problems (Beyer et al., 2001).
Managing nutrients in the diet can result in significant financial savings to the producer and limit environmental impact. Formulating feeds using the ideal protein concept, phase feeding and considering the type of poultry being fed will minimize diet cost while maximizing nutrient utilization by the animal. Feed digestibility can be improved by using feed processing or including feed additives to ensure that birds are utilizing all nutrients available. An increased awareness of feed management will minimize the amount of undigested feed that occurs in the litter and result in better management of the nutrients being fed to the birds. Therefore, the incorporation of these strategies will result in increased profits and reduce the impact of nutrients, especially phosphorus and nitrogen, on the environment.
This paper is from the 2009 Manure $ense guide. To download the entire guide click here.