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Author: ANGELE THOMPSON - Thompson PetTech (Courtesy of Alltech Inc.)
Publication date: 04/10/2007
New directions for the NRC book for companion animals
Three years ago, I spoke to this audience with great anticipation of the release of the National Research Council’s Nutrient Requirements for Dogs and Cats. I identified areas of nutrition research where gaps still existed in our knowledge and tried to predict some of the new information that might appear in the new NRC publication. While the release of the final document has been delayed until mid-2004, a pre-publication document was made available in November of 2003 (NRC, 2003). My excitement diminished after looking at the pre-publication. There is a tremendous amount of good work in the prepublication; but there were parts that gave me, as an end user of the document, serious concern. Let me stress to anyone attempting to use the pre-publication document, that it is NOT the final version. The NRC staff has been resolute that the final document will look exactly like the pre-publication document with the exception of editorial changes. I cannot predict what will be deemed an editorial change and what will not. My comments are based on the prepublication version with caveats. I have quoted the pre-publication document (as NRC, 2003) and these cited sections might be changed in the final version.
It has been nearly 19 years since the 1985 NRC Nutrient Requirements for Dogs was released. That edition contained 79 pages. The 1986 NRC Nutrient Requirements for Cats contained 78 pages. The 2003 pre-publication version of the new combined dog and cat edition contained 447 pages and had no index (NRC, 2003). The difference between the editions shows the immense amount of work done by the contributors to the document. The text was greatly expanded. The review of literature was extensive and the references are given. There are entirely new sections. The discussions include not only essential nutrients, but also non-essential nutrients. There are synergies in the combination of the two species allowing for the combination of basic information. However that same combination is often confusing in its organization, leaving the reader struggling to be sure which species is under discussion.
Each edition of NRC publications has a new and different expert committee chosen to write the publication. Each committee gets a slightly different charge for its job. The 2003 committee was told to use only peer-reviewed documents. The committee writing the 1986 NRC for cats was able to use ‘published research and practical experience’ (NRC, 1986). As quoted from the 2003 pre-publication overview, “This edition differs from the others because it contains the latest data on requirements, based on the utilization of nutrients in ingredients commonly produced and commercially available in dog and cat food rather than only on purified diets.”
The nutrient requirement tables in the 1985 dog book and the 1986 cat book were based on purified diets and at least in the cat publication, “A margin of safety was intentionally not incorporated…” (NRC, 1985; 1986). Thus, the nutrient requirement tables in the two earlier editions could not be put into practical use without adjustments and could not be used directly for regulatory purposes. This is one reason that the AAFCO Dog and Cat Food Nutrient Profiles were developed (AAFCO, 2004). In the text of the new edition, comments noted that for some values adjustments have been included to account for bioavailability, but not for all values. So, the 2003 publication appears to be related to practical diets but not in a consistent manner. It is important to remember that the nutrient values are recommendations for healthy animals and normal function, not for animals in disease states. The 2003 committee was made aware that the publication would be promoted for a wide variety of audiences: professionals in the industry, academia, students, government officials and pet owners. Thus, “…the committee chose to err on the side of caution and include adequate detail from the literature cited to provide a clear roadmap for how the recommendations were derived” (NRC, 2003). The publication is a serious scientific document addressing the complexity of nutritional science for dogs and cats. While there are knowledgeable individuals in the public audience, the publication is not casual, accessible reading. There is a vast amount in this new edition to digest.
The initial review of the pre-publication version by industry professionals found errors and raised serious questions about parts of the document. As with previous editions, the tables in this book must not be used in isolation from the text. The values in the tables are based on certain assumptions about energy content and do not translate directly to most products in the marketplace. This is especially important for government regulators, both in the US and in other countries, to know and understand. The Pet Food Institute has already received numerous inquiries from other countries wishing to use the publication for regulatory purposes. Regulators in the US are planning a review of the practical, usable AAFCO Dog and Cat Food Nutrient Profiles, once the final NRC document is available (AAFCO, 2004). That does not necessarily mean that the AAFCO Nutrient Profiles will change. It means that the latest information will be considered and may be incorporated. Other countries, in the past, have not used the AAFCO Profiles, but continued to rely on the NRC minimum requirement values to judge the nutritional adequacy of pet products. The values in the tables in this new edition of the NRC document should not be used directly for regulatory purposes.
This is a scientific document, not a regulatory document. I cannot state that strongly enough. Finally, some of you will have seen the newspaper headlines the morning after the press conference on the pub-publication release. “Pudgy Pets are Packing on Pounds,” cried the Wall Street Journal (Foley, 2003). “Chew on This: Pets are Pudgy, Too” exclaimed the Los Angeles Times (Mestel, 2003).
Yes, the publication does include a handful of paragraphs on obesity in dogs and cats in the morethan- 400 pages, but the vast majority of the document is NOT about obesity. As you will see below, it is about much more.
New topics included
Dogs and cats are complex organisms with many factors influencing their nutrient needs. This new edition tries to tell the entire story. The animal must eat the food, digest the food, absorb the components of the food and the body has to metabolize those components. In addition, nutrient needs are controlled by physical activity and various environmental factors. Four entirely new topics have been included: comparative digestive physiology, feeding behavior, special considerations for laboratory animals, and physical activity and climate. The new topics emphasize the broader view of this publication compared to past ones. No longer are the minimum requirements for the essential nutrients the entire purpose of the document. All of these factors are covered in the new edition, which should be considered a strength of the publication.
Changes to the tables of requirements
The traditional table of requirements, which in the past listed minimum requirements for growth and maintenance, has become multiple tables expanded to include reproduction. Each table now has a complicated four-category system of values, depending on the information available: minimal requirement, adequate intake, recommended allowance and safe upper limit. The requirements have new assumptions for specific body weights, and in lactation for specific numbers of kittens/puppies.
Footnotes are given for adjustment of the values when body weights or numbers of offspring change. There are new units appearing in the tables as well. Where the previous edition utilized percentages or parts per million on a dry matter basis plus amounts per 1000 kcal ME; the new edition has four types of units.
The requirements are represented as: amount per kg dry matter, amount per 1000 kcal ME, amount per kg body weight and amount per kg metabolic body weight (BW 0.75). These extra units were included to assist veterinarians in customizing dietary support for individual patients. In short, the tables look significantly different from those of past editions.
Essential nutrients
In my previous paper, I identified the following gaps that I thought might be covered in the new edition: taurine for cats (would such be listed for dogs?); linoleic acid for dogs; levels of calcium and phosphorus for large breed dogs; copper requirements for reproducing cats; and finally, vitamin K for cats.
I suspected that some of the other gaps in nutrient requirements would remain gaps. These included manganese for dogs, iodine and selenium for cats, the effect of interactions of minerals on availability, and vitamin requirements for reproduction. Taurine was included as an essential nutrient for cats with values given for minimal requirements.
Taurine has been extensively researched in the years since the last NRC edition. This research is well recognized in the publication. Taurine needs in dogs are discussed in the text, but a minimal requirement is not included in the table. The committee did not find peer-reviewed, dose-response experiments that supported the establishment of a minimal requirement. They did comment on the practice of inclusion of taurine in lower protein diets for dogs, which allows the maintenance of taurine pools.
Calcium and phosphorus levels in puppies of different breeds are discussed, which is good news. But the bad news is that the user of the tables must carefully read the text in order to set values in diets.
For example, a minimum calcium requirement for puppies is set in the table, with a footnote which states “For calcium and phosphorus, the need may decrease by up to 20% per unit energy between 60 and 100% of mature body weight. Values are for giant breeds and may be different in others (see text)” (NRC, 2003). This is an example of the complications inherent in setting nutrient requirements. The table of requirement values for growth of puppies is set using a model 3-month old puppy weighing 5.5 kg, consuming 1000 kcal ME per day, but the footnote says the calcium and phosphorus values are set for giant breed puppies. The last 3-month old St. Bernard puppy I saw weighed closer to 18 kg than 5.5 kg. A reading of the text shows “…a minimum requirement of 2.0 g Ca per 1000 kcal ME (8.0 g Ca per kg, 4000 kcal ME per kg) may be set as the minimum requirement of dietary Ca that will support normal growth in puppies of both large and small breeds.” The table value for minimal requirement is indeed 2.0 g Ca per 1000 kcal ME. The text additionally says that the recommended allowance of 3.0 g Ca per 1000 kcal ME (the value in the table) “should be sufficient for all breeds.” Why then the footnote? Perhaps the second part of the footnote refers to only one column of the table, which then would be more consistent with the text.
While there is a long discussion of fatty acids in the text (about which more will be discussed later), minimal requirements are not set for linoleic acid in either species, nor are minimal requirements given for arachidonic acid for cats. Adequate intakes are given for linoleic and arachidonic acids for both species. As I said three years ago, this gap in research on known essential fatty acids seemed so basic, and yet the needed research just was not done to allow the establishment of minimal requirements.
Despite some relevant research, a minimal requirement for copper is not set for cats during reproduction citing “…the absence of specific experimental data…” (NRC, 2003). The available data were reviewed, deemed not specific enough and only an adequate intake is listed in the table. Many of the trace minerals are in the same situation, adequate levels are set but not minimal requirements.
This is the case for both dogs and cats. The greatest number of minimum requirements for trace minerals is set for growth in both species. Clearly, trace mineral research is still an open area.
Several vitamin requirements remain open for both species. I had speculated that a vitamin K requirement might be set for cats, but while there are some data, the committee’s reports were not enough to set a minimal requirement value. Only one minimal vitamin requirement is set for dogs, which is for riboflavin in adult maintenance.
Although research had been done for various essential nutrients, the experiments did not fulfill the committee’s criteria needed to set the minimal requirements.
Non-essential nutrients
One of the two biggest categories of non-essential nutrients identified for consideration three years ago was omega-3 fatty acids (referred to in the text as n- 3 fatty acids). The 2003 pre-publication did recognize the importance of this area. The text discusses not only the details of the n-6 fatty acids: linoleic and arachidonic acids, but also includes the n-3 fatty acids: alpha-linolenic (ALA), eicosapentaeoic (EPA), and docosahexaeonic (DHA). The text states “Both n-6 and n-3 fatty acids are essential for dogs and cats.” However, it also states “A specific requirement for long-chain n-3 PUFAs (EPA and DHA) in adult dogs has not been identified to date.” Under some circumstances certain fatty acids were noted as conditionally essential. All of the above fatty acids are listed in the tables for both species and adequate intake values, (not minimal requirements) are set for all. Does inclusion in the tables recognize all these fatty acids as essential or not?
There is a listing for the combination of EPA and DHA in each of the tables. The tables for adult dogs, reproducing dogs and adult cats include a footnote regarding a general recommendation about the appropriate mixture of EPA and DHA for diets, at 30% of each. What then should the other 40% of n- 3 fatty acids be? How was this ratio established? The following statement is in the text section on adult maintenance of dogs “A general recommendation is that EPA and DHA should contribute approximately one-third each of the total dietary n-3 LCPUFAs.” No reference is given as to the source of this general recommendation and yet the charge to the committee was to only consider peer-reviewed publications.
The second big category identified for consideration three years ago was carbohydrates and fiber. The 2003 committee did a great deal of good work in this area. Carbohydrates as a nutrient category were covered in less than four pages total in both previous editions.
That has now been expanded to 35 pages with a complete discussion of all groups in the carbohydrate family. The category was divided into four groups: absorbable, digestible, fermentable and nonfermentable.
The text is quite detailed in its discussion of the utility, nutritive value, effects on growth and reproduction and physiological effects of each group of carbohydrates. It is interesting to note that while many important nutritional aspects of carbohydrates are discussed, there are no carbohydrates included in the tables; thus leaving the impression that while they play a definite role in dog and cat nutrition, they are still not considered essential nutrients. From the US regulatory perspective, the only recognition of carbohydrates in regulation is as crude fiber, a term not used in the text of the carbohydrates chapter. So carbohydrates are important in nutrition, but not classically essential, and not a simple nutrient class for regulatory attention.
Energy
The topic of energy received vast research attention between editions of the publication. As in the carbohydrates section, the 2003 committee made a great effort in the energy chapter. The four pages in the 1985 NRC for dogs and the three pages in the 1986 NRC for cats have become 26 pages in the 2003 edition. (NRC, 1985; 1986; 2003) The Holy Grail has been one energy requirement calculation equation for each species, which is clearly not appropriate based on the research. This is reflected in the tables, where energy requirement calculation equations for each species at each life stage are provided. These equations are much more sophisticated than those given in earlier editions. This approach is entirely consistent with the goal of providing end users the ability to individualize energy delivery to animals.
However, for regulatory purposes in labeling products with feeding directions, this level of complexity presents problems. The AAFCO Model Pet Food Regulations require that feeding directions be given on all pet foods labeled as complete and balanced for any and/or all life stages (AAFCO, 2004). These directions must be consistent with the intended use of the product. This means that if a product is labeled for all life stages, then feeding directions must be given for all life stages. In the 2003 NRC, there is one equation for weaned puppies and one equation for adult dogs but six multiplication factors determined by the dog’s activity level and breed. For late gestation, there is a two-part equation, while for lactation, there is another two-part equation that depends on the number of puppies and week of lactation. Those equations are all scientifically sound, but it will be difficult for a non-expert regulator to judge the appropriateness of the feeding directions on a label. In addition, how extensive do label feeding directions need to be? This will be for AAFCO Pet Food Committee and industry to work together to balance accurate science with usability for the consumer. This is another reason why the nutrient requirement tables in the 2003 publication should not be put directly in to use as regulation.
Safe Upper Limit (SUL)
This is the first appearance of SULs in the NRC for dogs and cats. In fact, SULs have not appeared in previous NRC publications such as those for swine, dairy cattle or beef cattle (NRC, 1998; 2000; 2001).
Those documents used the carefully defined words “maximum tolerable concentration” and did not include values in the requirement tables. There were too many conditions related to every value that had to be considered when applying it to a diet. The 2003 NRC dog and cat publication defines the SUL as “the maximal concentration or amount of a nutrient that has not been associated with adverse effects…” The inclusion of SULs in the tables is of great concern to industry professionals. The concept of upper limits is not foreign to the industry. The AAFCO Dog and Cat Food Nutrient Profiles include a few maximum levels for nutrients where valid concerns about toxic levels exist (AAFCO, 2004). Industry review of the pre-publication raised serious doubts about the usage of SULs as they appear in the 2003 NRC.
The logical interpretation of ‘safe upper limit’ by government officials and the public is that any product containing nutrients at levels higher than those given in the publication will harm animals. But that is not the way the values were developed. This is a major disconnect. Perhaps at least the name should be changed to better reflect the concept as used by the NRC. The origin of the values throughout the publication appears inconsistent, which indicates that the meaning of the SUL is inconsistent.
For example, three of the applications of the SUL concept are:
• absolute maximum where toxicity exists;
• upper level tested in research;
• an upper level tested in research with a safety factor added.
In some cases, the SUL represents the highest level tested in the research, but often no higher level was tested or shown to result in adverse effects. Thus, the highest level tested was set as the SUL, without knowledge as to whether or not a higher level would result in adverse effects. This seems misleading.
Some of the SUL values in the tables show a ‘greater than’ symbol in front of the value. Examples are zinc for adult cats, amino acids for kittens, lysine for puppies, sodium and iodine in adult dogs, etc. This appears to mean that the SUL is some unknown value above the value given. I do not see that including such a value in the table is reasonable. No limit is defined. Perhaps a footnote without a value noting that there is concern about potentially toxic levels for that nutrient would be appropriate.
Another concern with SUL is that some values were set based on a general rule of thumb, which is not equivalent to the “maximal concentration…not associated with adverse effects.” For example, the SUL for thiamin in both species was set based on a suggestion by NRC that the presumed safe upper limit would be 1000 times the dietary requirement (NRC, 1987). The text states “There are no reports of toxicity resulting from excessive oral intakes of thiamin, but intravenous thiamin in high doses can cause neuromuscular and ganglionic blockade” (NRC, 2003). If the SUL is for parenteral nutrition and not practical commercially available pet foods (the stated intent of the publication), then why is the value included or why is it not at least footnoted to acknowledge that fact?
Also of great concern is the inclusion of an SUL for total fat in each of the tables. This indicates that dietary levels above the stated value would be harmful to the animal. But the SUL for total fat was based only on the amount of fat that would result in a reasonable amount of space for protein at the given caloric content, not a direct safety concern for fat. In fact, the footnote for the SUL for total fat states “The upper limit of fat may be greater than values indicated because it is limited by protein concentration requirement in a diet designed to be 4 kcal ME per g DM. Any higher fat content would exceed this assumed caloric density.” (NRC, 2003). However for someone just looking at the fat level in the diet and looking at the table, a higher level of fat would be castigated as harmful. Perhaps this issue should be dealt with by inclusion of the footnote without a potentially misleading value. In the tables for dogs, there is a footnote for ALA in the SUL column. This footnote indicates a recommended ratio of LA to ALA and the ratio varies by life stage. In its discussion of SUL for LA and ALA, the text states “…so the ratio of LA to ALA is within the recommended range (see Table 5-1) “. There are no recommended ranges given in Table 5-1. Table 5-1 is entitled “List of Abbreviations of Selected Fatty Acids…” The reference regarding the ratios may be in the text; it is certainly difficult to find. One very troubling issue in the carbohydrates chapter was the last table, which set SULs for various ingredients for maintenance of adult animals. This is a clear departure from the rest of the publication.
SULs in the rest of the document are set for nutrients, not ingredients. The inclusion of SULs for ingredients can easily result in the included ingredients being identified as ‘unsafe’. This is a disservice to very healthy and useful ingredients. The definition used here for SUL is “a level of dietary inclusion at which no adverse effects can be expected.” (NRC, 2003) However, of the 23 SULs set for dogs in the 2003 NRC publication, 13 of the levels had the following footnote, “Higher levels were not tested.” Therefore there really are no data to say whether these 13 values 508 A peek into the new NRC for dogs and cats are or are not the SULs. This table also raises the potential for products currently in the marketplace, with histories of safe use, to be deemed ‘unsafe’, with no evidence that they are unsafe.
The concerns about SUL are not limited to the above, but they are some of the most visible issues. This concept and its use are of great concern. It is a serious, troubling possibility that government regulators or lay public could use SULs in inappropriate ways. SUL values, taken directly from the tables, cannot be utilized in a simple, across the board application to all products for the purpose of judging safety of the products.
Conclusion
I would like to thank the expert committee that put in many hours on a volunteer basis toward the completion of the publication. They were given a huge task. Much of the pre-publication document is worthwhile. However, there are areas of concern to at least one end user group, i.e., industry professionals. These areas of concern have been raised to the NRC staff and members of the industry have offered to work with the expert committee and NRC staff to help make this publication more sound and usable by the various target audiences. The NRC staff refused these offers.
I would also like to thank a group of very experienced nutrition professionals who dove in and reviewed the pre-publication document when it was released. These professionals came from all sectors of the industry. Their comments were valuable to me and I hope will be valuable in the future use of the final NRC publication.
We now await the final publication of the NRC Nutrient Requirements for Dogs and Cats. I think the peek at the pre-publication document gives us a very vital piece of information. There are still gaps in our knowledge of dog and cat nutrition. As noted in the overview, “ Gaps in our knowledge of specific requirements are noted in the text and by absence of data in the requirement tables.” One of the goals for this NRC publication is for “…identifying new topics for research.” I think those gaps are evident. Nutrition research for dogs and cats remains an active arena. We all have many opportunities and a lot of work still to do.
References
- Association of American Feed Control Officials. 2004. Official Publication. AAFCO, Oxford, IN. Foley, R.J. 2003. Pudgy Pets Are Packing on Pounds. Wall Street Journal Sept. 9, 2003.
- Mestel, R. 2003. Chew on This: Pets Are Pudgy, Too. Los Angeles Times. Sept. 9, 2003.
- National Research Council. 1985. Nutrient Requirements of Dogs. Revised. National Academy Press, Washington, DC.
- National Research Council. 1986. Nutrient Requirements of Cats. Revised ed. National Academy Press, Washington, DC.
- National Research Council. 1987. Vitamin Tolerances of Animals. National Academy Press, Washington, DC.
- National Research Council. 1998. Nutrient Requirements of Swine. 10th revised ed. National Academy Press, Washington, DC.
- National Research Council. 2000. Nutrient Requirements of Beef Cattle. 7th revised ed. Update. National Academy Press, Washington, DC.
- National Research Council. 2001. Nutrient Requirements of Dairy Cattle. 7th revised ed. National Academy Press, Washington, DC.
- National Research Council. 2003. Nutrient Requirements of Dogs and Cats. Prepublication copy. National Academy Press, Washington, DC.
Author: ANGELE THOMPSON
Thompson PetTech, New Providence, New Jersey, USA
Author: ANGELE THOMPSON - Thompson PetTech (Courtesy of Alltech Inc.)
Publication date: 04/10/2007
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