Summary

During the past 80 years, the Nutrient Requirements of Poultry reports have sequentially documented our understanding of most commonly used practices in poultry nutrition and have continually become longer and better referenced, and they include more background information, but their frequency of publication has declined (Applegate and Angel, 2014; Bailey, 2020). The scientific rigor and transparency of decision processes for specific recommendations have also increased with time. The committee agreed to follow the previous standard of relying exclusively on peer-reviewed sources and the committee’s own original analysis for their recommendations, but sometimes readers are referred to other sources for background information.

It has been 31 years since the publication of the previous update (NRC, 1994), and the committee had a sizable assignment. The research, computer modeling, and writing of this report took a little over 7 years, during which the committee had five in-person meetings and several dozen video conferences. The previous edition of this report (NRC, 1994) provides documentation for peer-reviewed studies that were used for their recommendations, and that report can be consulted for access to the older literature.

The target audience of these reports continues to be professional nutritionists in industry and academia, veterinarians, government regulators, the judicial system, and instructors and students in poultry science. This new report has 21 chapters and updates nutrient recommendations for the same poultry species covered in the previous report. There is also increased attention to broiler breeders, ducks, geese, and Japanese quail. This new report provides considerably more background information specific to poultry, including some recent global production statistics, a nutritional perspective on their domestication as well as strain characteristics, gastrointestinal physiology, nutritional quality of products, feed processing, environmental considerations of poultry diet formulation, and the effects of stress on nutrient requirements. Additionally, computer models based on the application of the relationship between rates of tissue deposition or egg production and tissue and egg nutrient composition were developed to predict amino acid requirements of broilers and layers. Models for turkeys were considered, but ultimately the committee decided that there was insufficient knowledge and expertise to develop that approach. The committee also allied with the U.S. Department of Agriculture–supported National Animal Nutrition Program-9 (NANP-9) for managing databases involving modeling efforts and nutrient composition of feedstuffs that are provided in this report with the goal of enabling greater access, transparency, and frequency of updates.

The committee also focused on increasing the transparency of how publications were selected to develop or update nutrient recommendations and digestibilities and bioavailabilities of nutrients. The committee established general criteria for publication suitability. The committee’s general criteria are summarized subsequently and were adhered to when an adequate number of high-quality research publications were available. However, literature gaps were frequently encountered by the committee, and individual chapters provide additional qualifications and guidance for inclusion or exclusion of research reports used to develop recommendations as needed. Furthermore, the committee agreed with the approach used in the previous reports that more speculative guidance should be provided where necessary to give safe levels of dietary nutrient concentrations for situations where there were few publications that met the stringent list of inclusion criteria. Recommendations based on speculative guidance are clearly identified in the text and by the fonts used in the tables.

TRANSPARENCY OF SELECTION CRITERIA AND CONFIDENCE LEVEL OF RECOMMENDATIONS

To the extent possible, the committee adhered to strict criteria for deciding if a research study should be included as supportive data to develop a recommendation on a nutrient requirement. The criteria were based on details of experimental

design and data analysis including the following: (1) A common basal diet was employed across all treatments; (2) a sufficient number and range of nutrient additions to the common basal diet were included to establish a dose–response relationship below the requirement followed by a plateau indicating that the requirement had been met; (3) dietary concentrations of the nutrients of interest were chemically analyzed using appropriate techniques, including the amount determined in the unsupplemented basal diet; (4) the experimental design and statistical analyses were appropriate for estimating nutrient requirements, and sufficient methodological information was provided to allow for replication of the experiment; (5) management practices and environmental conditions were employed that did not impair animal performance; and (6) the response criteria of these studies were based on the dietary amount that resulted in optimal performance and avoidance of signs of deficiency, whichever was lowest. Differences in the availability of research reports to meet the committee’s criteria for inclusion led to differences in confidence for individual nutrient recommendations.

There is a high degree of confidence for those nutrient recommendations based on three or more research reports that met all the committee’s stated criteria. Furthermore, the committee asserts that such recommendations are accurate for the genetic, management, and dietary conditions under which the experiments were done. The dietary concentrations recommended with a high degree of confidence are indicated by normal font within tables and were set by averaging the estimates from all studies that met the inclusion criteria. Conditions that produced nutrient recommendations with a lower degree of confidence are described subsequently. Recommendations with a lower degree of confidence are explained in the text, and this lower level of confidence is signified in bold and italicized fonts within the tables.

For cases where there were insufficient studies available that met the foregoing inclusion criteria, but there were one or more studies that met most of the stated criteria, the Committee provides guidance at a moderate level of confidence. These exceptions were made so that a rough estimate of a nutrient requirement could be provided. There is not a high degree of confidence that these recommendations provide an optimal concentration in a least-cost ration formulation, but they are likely to support adequate bird performance. Other situations from which guidance values were derived include the following: (1) For some nutrients, there were studies that did meet the foregoing inclusion criteria, but supplementation of the basal diet produced no beneficial response and the nutrient concentration within the basal diet was acceptably analyzed. In that setting, the committee concluded that the basal diet had an adequate amount of the nutrient under study. In these cases, nutrient recommendations are based on the amount of the nutrient in the basal diet. (2) Many of the published experiments designed to titrate the requirement for various nutrients analyzed the results using analysis of variance followed by mean comparisons and did not use analysis by broken line regressions or other valid regression approaches to quantitatively estimate a requirement. In those cases, the committee used the highest level that was statistically superior to lower levels. (3) For species such as geese, ducks, and pheasants, additional accommodations were made as described in those chapters due to the paucity of well-designed studies.

NUTRIENT REQUIREMENTS

The National Academies’ recommendations differ from most other sources of nutrient requirements in that they are meant to be minimal levels for optimal production and avoidance of signs of deficiencies. The recommendations from many other organizations or companies typically include a margin of safety to account for problems related to feed mixing errors, ingredient variation, environmental stresses, genetic variation, nutrient degradation during storage, and undocumented field or research experience. The impacts of many of these factors are reviewed in Chapters 8 to 11, and nutritionists are accordingly advised to add a margin of safety to their requirement matrix. Moreover, the reader is reminded that the derivation of the committee’s recommended nutrient requirements was constrained by only considering data reported in peer-reviewed publications.

In the case of broilers, requirement recommendations are based on weight instead of age to allow more accurate use across breeds that have different growth rates and across the many different management systems that result in different growth patterns. This was not done for the other species, mostly because research publications often reported the beginning and ending age and the rate of gain but failed to report either the beginning or final weights. A significant conclusion of the committee was that the research community must always report beginning weights in addition to rates of gain so that requirements can be made on a weight basis instead of an age basis, thus permitting more accurate applications with changes in genetics and differences in production practices. Adoption of this simple obligation would support needed efforts in developing nutrient requirement models.

REQUIREMENT TABLES

The nutrient requirement tables are designed so that the level of confidence the committee has in specific recommendations can be quickly discerned. This is done by the use of different fonts (normal font versus bolded and italicized font) and shading. Values with a higher degree of confidence are provided using normal font, and the text indicates the reason for this confidence. Guidance recommendations are signified by bold and italicized font. Where no relevant new information exists since the previous report (NRC, 1994), the recommendations were carried over from that report and are signified by shading.

DOCUMENTATION OF THE LITERATURE TABLES

For broiler chickens, broiler breeders, laying hens, turkeys, ducks, geese, and minor species, there is a table at the end of each respective chapter that documents all of the studies that were considered in the compilation of the recommended nutrient requirements, including the ages, weights, sexes, and breeds of the birds used in the studies. Additional information on the composition and content of metabolizable energy and protein of the basal diets, range of nutrient amounts supplemented, statistical approaches, response criteria examined, and confounding factors are also reported. These tables provide much more detail on specific studies than the text and are meant to allow the reader to adjust their requirement recommendations to their specific applications.

REFERENCES

Applegate, T.J., and R. Angel. 2014. Nutrient requirements of poultry publication: History and need for an update. Journal of Applied Poultry Research. 23:567–575.

Bailey, C.A. 2020. Chapter 21—Precision poultry nutrition and feed formulation. In Animal Agriculture. F.W. Bazer, G.C. Lamb, and G. Wu, editors. Academic Press. 367–378.

NRC (National Research Council). 1994. Nutrient Requirements of Poultry, 9th rev. ed. Washington, DC.: National Academy Press.