National Academies Press: OpenBook

The Role of Chromium in Animal Nutrition (1997)

Chapter: Executive Summary

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Suggested Citation:"Executive Summary." National Research Council. 1997. The Role of Chromium in Animal Nutrition. Washington, DC: The National Academies Press. doi: 10.17226/5778.
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Suggested Citation:"Executive Summary." National Research Council. 1997. The Role of Chromium in Animal Nutrition. Washington, DC: The National Academies Press. doi: 10.17226/5778.
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Suggested Citation:"Executive Summary." National Research Council. 1997. The Role of Chromium in Animal Nutrition. Washington, DC: The National Academies Press. doi: 10.17226/5778.
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Suggested Citation:"Executive Summary." National Research Council. 1997. The Role of Chromium in Animal Nutrition. Washington, DC: The National Academies Press. doi: 10.17226/5778.
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Suggested Citation:"Executive Summary." National Research Council. 1997. The Role of Chromium in Animal Nutrition. Washington, DC: The National Academies Press. doi: 10.17226/5778.
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Executive Summary For approximately 40 years, chromium has been considered by many nutri- tionists as an essential nutrient for humans and animals. Chromium, which exists in nature mostly in the trivalent form (Cr+3), is thought to be essential for activating certain enzymes and for stabilizing proteins and nucleic acids. Its primary role in metabolism, however, is to potentiate the action of insulin through its presence in an organometallic molecule called glucose tolerance factor (GTF). Evidence for the importance of chromium has been obtained primarily from research and clinical investigations with humans and laboratory animals. People who receive parenteral nutrition and those who are type II diabetics respond well to chromium supplementation. Research also has shown that supplemental di- etary chromium is beneficial for humans and laboratory animals undergoing various stresses. Research with animals has confirmed that chromium from dietary organic complexes, such as chromium picolinate (CrPic), chromium nicotinate (CrNic), and high-chromium yeasts, is absorbed more efficiently than is chromium from chromium chloride (CrCl3~. Some research data indicate that chromium is an essential nutrient for food-producing and laboratory animals. Responses of ani- mals to chromium supplementation of practical diets, however, have varied, and the role of chromium in animal metabolism has not been clearly established. Presumably, chromium would function as a component of GTF, as suggested for humans and laboratory animals.

2 THE ROLE OF CHROMIUM INANIMA:L NUTRITION RUMINANTS Bioavailability of chromium contained in commercial feeds for ruminant animals is not known. Further efforts need to be directed toward the determina- tion of chromium concentrations and chromium bioavailability in foodstuffs and chromium supplements offered to ruminant animals. A range of chromium supplements including CrNic, CrCl3, CrPic, chelated chromium, and high-chro- mium yeast have been used in ruminant studies. Few comparative studies have been conducted, and thus, little is known about the relative bioavailability of these sources for ruminants. Performance responses observed to date are limited to work conducted with CrPic, high-chromium yeast, and chelated chromium. The literature does not support a general recommendation for chromium supplementation of commercial ruminant diets. Research efforts, however, have identified two situations in which chromium supplementation might have com- mercial application: newly arrived feedlot cattle and first lactation dairy cattle during the transition period. Three out of eight studies conducted with newly arrived feedlot cattle sub- jected to the stresses of transportation, mixing, and handling have demonstrated a positive performance response in the initial weeks following arrival. Lower morbidity and plasma cortisol concentrations due to chromium supplementation have been reported; however, the responses have not been consistent. Efforts to establish enhanced immunity in response to vaccination or to foreign proteins have not shown consistent results, although blastogenesis in peripheral blood mononuclear cells cultured with T-lymphocyte mitogens was greater in cattle fed chromium-supplemented versus unsupplemented diets. The transition period, including late lactation, parturition, and early lacta- tion, is known to cause metabolic stress in dairy cows. There is evidence that chromium supplementation during this transition period can improve performance of first-lactation cows. This response was not observed in multiparous cows offered similar levels of supplemental chromium. Improved performance may be associated with a shift in ketone body metabolism, because lower circulating ketone concentrations in cows consuming chromium-supplemented diets have been observed in several studies. There also is evidence that chromium provided to first-lactation, postpartum cows will decrease sensitivity to insulin. As was observed with stressed, newly arrived feedlot animals, blastogenic responses of the peripheral blood mononuclear cells obtained from chromium-supplemented, early lactation cows were enhanced. Controlled studies will be required to establish the specific role of chromium in cattle undergoing stress. These studies are essential to establish recommenda- tions for rates of chromium supplementation where its use may be appropriate. Work involving sheep suggests that chromium supplementation exerts subtle effects on carbohydrate and lipid metabolism. The significance of these effects, however, is not clear.

EXECUTIVE SUMMARY 3 NONRUMINANTS Responses of growing-finishing swine to supplemental dietary chromium have been inconsistent. Improvements in growth rate of swine as a result of supplementing diets with 200 to 500 ,ug Cr/kg as CrPic or 500 ,ug to 5 mg Cr/kg as CrCl3 were reported in 11 of 31 studies. Similarly, feed efficiency was im- proved by chromium supplementation of diets in 8 of 31 studies. Favorable effects of added chromium on selected carcass traits have been observed. When supplemental dietary chromium was used, increases in carcass leanness (mus- cling) were reported in 9 of 24 experiments and decreases in carcass fat were observed in 11 of 26 experiments. Research to determine the influence of added dietary chromium on reproductive performance has been meager, and the results have varied (litter size was increased in one experiment, but reproductive traits were unaffected in a second study). Information on the metabolic changes that may be caused by supplementing swine diets with CrPic also is limited. Three experiments provide evidence to suggest that supplemental CrPic induces a hy- poglycemic response or improves insulin efficiency in swine. Although responses of swine to supplemental chromium have been inconsistent, there is an increasing amount of evidence indicating that chromium may favorably alter metabolism of swine under some circumstances, with resultant improvements in growth rate, carcass traits, and reproductive performance. The need for chromium supple- mentation of practical swine diets, however, depends on the chromium status of the animals, the amount of biouvailable chromium in the feedstuffs, and exposure of the animals to certain environmental stresses. Thus, a decision to use supple- mental chromium in practical swine diets must be based on the potential benefits in individual circumstances versus the cost of supplementation. Evidence has been obtained that supplemental chromium at 20 mg/kg of diet as CrCl3 increases the rate of glucose utilization by livers of chicks and poults in vivo and in vitro. The effects of added dietary chromium on growth rate and feed efficiency of growing poultry have differed, with improvements reported in 4 of 11 experiments. An improvement in performance of young poultry was observed when CrCl3 was used to supply 20 mg Cr/kg of diet. Supplemental dietary chromium as CrPic also has been reported to decrease mortality and cholesterol in serum and egg yolks and to alter glucose metabo- lism of chickens. Research with poultry has shown that supplemental dietary chromium can be used to alleviate some of the toxic effects of vanadium in growing chicks and laying hens. The evidence available today, although meager, indicates that supplemental dietary chromium can affect metabolism and well-being of poultry. Additional information is needed, however, to describe the circumstances in which supple- mental dietary chromium can be used to greatest advantage. A limited amount of research has been conducted to determine the effects of chromium supplementation on performance and metabolic responses of horses.

4 THE ROLE OF CHROMIUM INANIMA:L NUTRITION The meager amount of research conducted with horses has not shown any defini- tive benefits of dietary chromium supplementation. Chromium has been shown to be essential for glucose metabolism in rats under controlled experimental conditions in which body stores of chromium were depleted. Mainly on this basis, chromium was addressed in the National Re- search Council's publication, Nutrient Requirements of Laboratory Animals, as a potentially beneficial dietary constituent for rats. A dietary requirement per se, however, was not given, and no benefit from chromium supplementation of prac- tical rat diets was indicated. Research with rabbits indicates that cholesterol and plaque content of the vascular system was decreased by supplemental dietary chromium and that chro- mium metabolism can be modified, depending on the dietary carbohydrate source. There is, however, insufficient information on which to base conclusions or recommendations concerning the need to supplement rabbit diets with chromium. Investigations into the influences of supplemental dietary chromium on fish have been limited. Some studies report no effects of dietary chromium supple- mentation on growth or tissue chromium distribution in several fish species. Other studies, however, show that chromium supplementation of diets, especially those containing glucose, causes significant increases in weight gain, energy deposition, and liver glycogen of fish and alters postprandial plasma glucose concentrations. Thus, it seems that chromium plays a role in glucose metabolism of fish as has been reported for some other animals and humans. Specific mecha- nisms by which chromium influences dietary carbohydrate utilization of fish, however, have not been elucidated. CONCLUSIONS The Committee on Animal Nutrition has reached the following conclusions. (1) It is not possible to make specific recommendations as to dietary form and concentration of chromium supplementation for cattle, poultry, and swine because · there are insufficient comparative data for the determination of relative biouvailabilities of chromium from supplemental sources; · only meager data are available from titration studies designed to deter- mine supplemental chromium concentrations that are most effective for cattle, poultry, and swine; and · there have been no studies designed or conducted to determine dietary chromium requirements of cattle, poultry, or swine. (2) Supplementing practical diets with trivalent sources of chromium might be beneficial for the health and well-being of cattle during times of stress; how- ever, the factors that affect the efficacy of supplemental chromium and the dietary chromium concentrations required have not been determined.

EXECUTIVE SUMMARY s (3) Chromium supplementation of swine diets, beginning at an early age and continuing through thefinishing period, could improve carcass leanness and subsequent reproductive efficiency, but these responses to chromium are likely to be inconsistent until the factors that affect the efficacy of dietary chromium inclusion are more clearly defined. (4) Information in the scientific literature on the need for supplemental chromium in practical diets offish, horses, sheep, rabbits, and rats is too sparse to allow conclusions. (5) Although most research on potential toxicity of trivalentforms of dietary chromium has been conducted with rats and chickens, the results show that the concentrations of trivalent chromium typically added to diets offood-producing animals are safe and nontoxic. (6) Additional research is needed to determine the biouvailability of chro- mium contained in feed ingredients and to obtain more definitive data on the comparative biouvailability of chromium from dietary supplements. (7) Research should be designed to create reproducible signs of chromium deficiency in animals, which would facilitate the establishment of dietary chro- mium requirements by way of appropriate titration studies. Successful determination of dietary requirements will depend partly on es- tablishment of procedures for chromium analysis of foodstuffs and diets that are sensitive and that will yield reproducible results. Research also should be planned to control and measure the impact of factors suspected of contributing to incon- sistent responses of animals to chromium supplementation of practical diets. This research would make it possible to document the circumstances in which supplemental dietary chromium could be used to best advantage.

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The American feed industry manufactures tons of dietary supplements and additives each year for inclusion in the diets of food-producing animals. Some scientists have suggested that chromium should be a key ingredient in nutritional supplements. Controversy exists, however, over whether chromium sources should be approved as feed additives and whether enough data exist to establish dietary requirements. Chromium use has been suggested to have positive impacts on farm profitability, and many animal health benefits have been attributed to chromium supplementation, including increased longevity; enhanced reproduction; decreased incidence of metabolic disorders, stress effects, and disease; reduced need for antibiotic usage; improved immune response; and lean carcass quality.

This book addresses recent research on chromium in animal diets; metabolic interactions between chromium and other nutrients; assessments of form and species interactions; supplementation effects; bioavailability of chromium forms and sources; and effects of diet composition, stressors, and animal physiological status on chromium utilization. It also provides recommendations on the essentiality of dietary chromium in domestic animal species and guidelines for use of dietary chromium.

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