Organic Chromium in Poultry
Organic Chromium in Poultry: Metabolic Responses, Effects on Broiler Carcass Composition, Nutrient Composition of Eggs
In recent years there has been considerable research interest in utilization of chromium (Cr) in animal feed. Beneficial effects of Cr in human health are well documented and include a role in maintenance of normal blood sugar and cholesterol levels. Chromium, as an integral component of the glucose tolerance factor (GTF), helps control appetite, hypoglycemia and protein uptake and plays a protective role against heart disease and diabetes (Mertz, 1993). The hormone insulin regulates energy metabolism, muscle tissue deposition, fat metabolism and cholesterol utilization. If glucose cannot be utilized by body cells due to low insulin activity, it is converted into fat cells. Furthermore, if adequate amino acids cannot enter the cells, muscle cannot be built (Anderson, 1988).
In the field of animal nutrition, there is emerging evidence to suggest that pigs and poultry may have a dietary requirement for Cr that exceeds that found in a cornsoybean meal diet. Recent findings on the positive effects of Cr supplementation for pigs on carcass leanness and on reproductive parameters have been quite impressive. Published research on the effect of Cr supplementation on poultry performance and meat and egg quality is more limited.
Metabolic responses to chromium
The valence state in which Cr is present in tissues and body fluids determines its biological function. Chromium is most stable in the trivalent state (Cr+3) which is considered to be the only physiologically active form of the element. The magnitude of this activity depends on the particular complex or compound in which Cr is bound. Chromium compounds can be classified into two major categories: the first category contains simple compounds such as chloro, aqua, or acetate complexes of Cr or complexes with amino acids, sugars, organic acids, or certain vitamins.
The second category contains natural Cr complexes such as occur in yeast and in foods. This group exhibits the highest magnitude of biological activity; and trivalent Cr in this form is known as the ‘glucose tolerance factor’ or GTF. GTF purified from brewers yeast has a molecular weight between 300 and 500 Da and is water soluble and heat stable. This substance is known for its potentiating effect on insulin (Mertz et al., 1974). This aqua complex is unstable in solution, but the stabilization of Cr complexes can be achieved by replacing the coordinated water molecules with ligands.
The presence of three amino acids in the purified yeast fraction suggested that the four coordination sites of Cr may be linked to amino acids to achieve stabilization. The analysis of highly purified GTF preparations from yeast indicated the structure of GTF as a di-nicotinate, tri-amino acid, Cr+3 complex (Toepfer et al., 1973). The predominant amino acids are glycine, cysteine, and glutamic acid, the components of glutathione (Mertz, 1992). Reacting these amino acids with Cr-niacin complex yields compounds that have stability and a biological activity equal to or even greater than the tetra-aqua, di-nicotinate Cr complex.
Inorganic Cr compounds are poorly absorbed in animals and humans. Absorption ranges from 0.4 to 3% or less, regardless of dose and dietary Cr status (Anderson et al., 1983). Inorganic Cr salts, even those containing Cr+3, are absorbed very poorly (»1%). On the other hand, GTF Cr is absorbed at about 15–20%. According to Mowat (1997), bioavailability of organic Cr is around 25–30%. Chromium in Cr yeast is considered to be non-toxic (Flodin, 1988). The therapeutic:toxic dose ratio for trivalent Cr is about 1:10,000 and therefore Cr is considered to be a highly safe trace element (Mowat, 1997).
The site or mechanism of Cr absorption is not yet known. In the rat the midsection of the small intestine appears to be the most diffusible segment for Cr, followed by the ileum and duodenum. Following absorption Cr is probably transported on the iron-carrier protein of blood plasma, transferrin. It is not known whether GTF absorbed through the intestine enters the blood as GTF or also binds to transferrin. From the intestine, most of the Cr proceeds to the liver, where it may be incorporated into GTF. A certain amount of GTF is secreted into plasma where it is available to help the action of insulin. When blood glucose levels rise, insulin is secreted, GTF levels increase and Cr flows into plasma (Linder, 1985). GTF Cr enhances the effect of insulin in moving glucose from the bloodstream into cells and then is lost in the urine. Hahn and Evans (1975) suggested that Cr and zinc may be metabolized by a common pathway in the intestine. The presence of these two metals in the same mucosal supernatant fraction and their similar behavior on an anion exchange column support this suggestion.
The presence of amino acids, ascorbic acid, high levels of sugars, oxalate and aspirin in the diet enhances Cr absorption while phytate and antacids seems to reduce Cr in blood tissues (Hunt and Stoecker, 1996).
Chromium excretion, mainly via the urinary tract, may increase 10 to 300 fold in stress situations or if dietary sugar content is increased. This also becomes nutritionally important because in such conditions it is necessary to increase the trace element concentration in the diet (Anderson, 1994).
As Cr acts as a cofactor for insulin, all the actions of Cr directly parallel those of insulin (Fisher, 1990). Although insulin (and Cr) perform various functions in animals and humans, the three major functions are to aid in the regulation of carbohydrate, protein, and fat metabolism. Insulin facilitates the entry of glucose from the blood into liver and muscle cells where it is stored as glycogen and into fat cells where it is stored as triglyceride. Chromium increases or potentiates insulin activity, but it is not a substitute for insulin. In the presence of organic forms of Cr, much lower levels of insulin are required to elicit similar biological responses (Mertz, 1993). Insulin increases the uptake of amino acids and promotes the assembly of amino acids into protein through its effect on DNA and RNA synthesis.
Chromium appears to be involved in gene expression by binding to chromatin causing an increase in the number of initiation sites and thereby enhancing RNA synthesis. This enhancement is caused by induction of a nuclear-bound protein and by activation of nuclear chromatin (Okada et al., 1989). The net effect is increased protein available for building muscle tissue. Testosterone, the substance from which anabolic steroids are derived, does have anabolic effects, but they are secondary to those of insulin. Insulin is the body’s primary anabolic hormone and Cr is necessary for insulin to help build muscle (Moorandian and Morley, 1987).
Insulin’s effect on fat metabolism is complex. It helps regulate the balance between the blood and storage forms of cholesterol and triglycerides. There is evidence that links marginal Cr intake with abnormal lipid metabolism and consequently artherosclerosis in humans and animals (Schroeder, 1975; Abraham et al., 1991).
Effects of chromium on broiler carcass composition
Published research related to Cr supplementation of poultry diets is more limited than that involving ruminants, pigs or laboratory animals; however most of the studies prior to 1991 evaluated inorganic Cr effects on poultry. Steele and Rosebrough (1979) conducted an experiment to determine if Cr+3 and (or) nicotinic acid affected growth rate and feed efficiency of young turkey
poults. The addition of 20 ppm trivalent Cr (CrCl3.6H2O) or 250 ppm nicotinic acid significantly improved weight gain compared to the unsupplemented corn soybean meal basal diet over a 14 day feeding trial (Table 1). No additive effects of Cr+3 and nicotinic acid supplementation were observed. Therefore, both Cr and nicotinic acid may have unique effects on poult growth and development though synergism between Cr and nicotinic acid is not present.
Table 1. Effect of Cr+3 and nicotinic acid on weight gain and feed efficiency of turkey poults.
The lack of an additive effect suggests that dietary Cr+3 must be in organic form for such response. Since the effect of insulin on carbohydrate metabolism in the bird is minimal, Rosebrough and Steele (1981) studied the effects of supplemental Cr and nicotinic acid during basal diet feeding, 48 hour starvation and re-feeding periods in turkey poults. They found that Cr supplementation of 3-week-old poults increased weight and feed intake and also increased liver glycogen during the basal and re-feeding periods though not during the starvation period when compared to supplemental nicotinic acid. A growth promoting effect of supplemental dietary Cr was also reported by Steele and Rosebrough (1981) in turkey poults.
Mertz (1969) proposed that Cr+3 functions by enhancing the binding of insulin to tissue receptors, thus stimulating insulin-sensitive processes. It was commonly thought that glucagon played a more important role than insulin in the control of intermediary metabolism in chicken. More recent findings (Simon, 1988) suggested that birds are mainly dependent on glucagon in the fasting state and insulin in the fed state. Chicken insulin is about twice as potent as mammalian insulin (McMurtry et al., 1983). Chicken insulin binds to the insulin receptor of rat liver membrane to a great extent than porcine insulin. Both insulins compete for the same number of receptors, and chicken insulin exhibits about two fold higher affinity for the receptor compared to porcine insulin (Simon et al., 1977).
Insulin sensivity of various rat tissues has been attributed to the presence of high Km-glucokinase in those tissues; and Leveille andYeh (1972) reported that high Km-glucokinase does not exist in chick liver. Whether or not the kinase activity of the insulin receptor represents the first step in signaling the message of insulin remains to be established in chickens (Simon, 1988). Steele and Rosebrough (1981) have examined the effect of Cr+3 on hepatic lipogenesis from glucose and acetate in poults to determine the stage of glucose metabolism where Cr affects lipid biosynthesis. They found that conversion of glucose to acetyl-CoA (decreased acetate/glucose ratio) in vitro was increased by Cr+3, whereas conversion of acetyl-CoA to fatty acids (acetate incorporation) was unaffected, thus suggesting that Cr+3 enhanced the uptake of glucose (Table 2).
Table 2. Effect of dietary Cr+3 supplementation on in vitro fatty acid synthesis by poult liver.
Anderson and Kozlovsky (1985) reported that absorption of Cr is inversely related to dietary intake at normal dietary intakes of less than 40 μg/day. Absorption of Cr was approximately 2% at intakes of 10 μg/day and only 0.4–0.5% when intakes were 40 μg/day. Therefore, the amount of Cr excreted in the urine, which is a measure of Cr absorption, was relatively constant at approximately 0.2 μg/day. To increase the potential intake of Cr from edible poultry meat, Anderson et al. (1989) fed 33-week-old turkey hens either a corn-soybean meal basal diet (Cr concentration 506±59 ng/g) or the basal diet supplemented with 25, 100, or 200 μg of Cr as CrCl3.6H2O. Supplementation of the diet with Cr led to a linear increase of Cr only in liver and kidney (Table 3). In the main edible tissues of breast and leg the increases were too low to allow these tissues to be used as suitable source of high-Cr foods for humans.
Ward et al. (1993) reported a tendency for 200 ppb Cr from Cr picolinate to increase protein percentage and decrease fat percentage in carcasses of 3-week-old broiler chicks.Ward and Southern (1995), using 0, 400 and 1600 ppb organic Cr in broiler diets between 1 and 49 days found a linear effect of Cr on feed conversion during the first 21 days and a quadratic effect on feed conversion and gain during the last 7 days. Dietary Cr was also found to decrease glucose, quadratically increase plasma insulin and linearly decrease non-esterified fatty acids in plasma 2 hours post-feeding. They concluded that dietary Cr from Cr picolinate affected growth, metabolism and carcass composition of broilers. Hossain (1995) reported that supplementation of 400 ppb of Cr from Cr yeast (BioChrome, Alltech, Inc.) reduced breast meat fat content and mortality (Table 4).
In another study conducted at the Federal University of Minas Gerais in Brazil, Hossain et al. (1997) observed that the body weight of broilers at 3 and 6 weeks was significantly influenced (Table 5) by the level of Cr in the diet. The highest body weight was observed with 300 ppb Cr from Cr yeast in the diet. Feed conversion was unaffected by dietary Cr throughout the trial. Harper et al. (1995) and Lindemann et al. (1995) reported an improvement in daily gain and feed utilization of post-weaning pigs with 200 ppb Cr from Cr picolinate. Page et al. (1993) reported that 200 ppb Cr from Cr picolinate increased muscle mass and reduced backfat thickness in pigs.Asimilar result was also reported by Mooney and Cromwell (1995). In heavy pigs, Cr yeast was found to be effective in improving feed efficiency, average daily gain and lean cuts (Savoini et al., 1996).
Table 3. Effects of dietary Cr supplementation on concentration of Cr in turkey tissues.
Broilers receiving diets containing 300 ppb Cr from Cr yeast had significantly higher carcass yield (Table 6). Carcass composition as assessed by absolute weight of the abdominal fat pad did not differ significantly; but when fat pad weight was expressed as a percentage of carcass weight, broilers given 300 ppb Cr had significantly less abdominal fat. Breast meat yield expressed in absolute terms or as a percentage of carcass weight was significantly increased with Cr supplementation (Figure 1).
Since effects on broiler carcass composition are cumulative, the length of feeding and market age are important factors in determining effects of Cr on carcass composition. This is evident from the fact that in two trials (Tables 4 and 6) the improvement of breast meat yield was 7 and 11% of the control, respectively. The positive effects of Cr on amino acid incorporation and utilization (Roginski and Mertz, 1969) and nuclear protein synthesis (Okada et al., 1984; Ohba et al., 1986) are well documented. The mode of action of Cr in affecting nuclear protein synthesis to influence carcass composition of broilers is not yet established.
Figure 1.Effect of dietary chromium level from Cr yeast (BioChrome) on breast meat yield as a percentage of carcass weight.
Table 4. Effect of chromium yeast (BioChrome) on broiler performance and carcass quality.
Table 5. Performance of broilers from 0–6 weeks of age with added Cr in the diets.
Mortality was significantly reduced with 400 ppb Cr from Cr yeast in one trial and 300 ppb in another trial (Figure 2). Reduced mortality may be related to the beneficial effect of Cr on immune response. Reduced morbidity in response to Cr supplementation is well documented with calves (Burton et al., 1993; Chang et al., 1995) but no such data are available with broiler chicks. The NRC (1994) did not specify any recommendation for Cr in poultry diets, which are basically composed of ingredients of plant origin containing only small amounts of Cr (Giri et al., 1990). Broilers reared in high environmental temperatures on corn-soybean meal diets probably have a moderate Cr deficiency. For better performance and carcass quality, broiler diets should be supplemented with bioavailable forms of Cr. Supplementation of Cr from Cr yeast offers a non-nitrogenous method of improving breast meat yield and carcass leanness.
Figure 2. Effect of dietary chromium level from Cr yeast (BioChrome) on mortality of broilers in two trials.
Table 6. Carcass characteristics of broilers with different levels of chromium yeast (BioChrome) in the diets.
Effect of chromium on egg composition
Over the past two decades considerable efforts have been made to improve the growth rate of meat birds and egg production of layers. For the last few years, however, there has also been discussion of nutrient requirements not only in terms of production but also in terms of altering the nutritional composition of poultry products as they relate to human health and consumer demand. This scrutiny has been a major problem to the egg industry, especially when added to the negative publicity concerning the cholesterol content of eggs. As it was stated earlier, in both animals and man Cr deficiency is characterized by glucose intolerance, elevated serum cholesterol and triglyceride, and sclerotic aortic plaques.
As a result, there is a growing interest in the potential effects of Cr on egg composition. Significant improvement in egg yolk quality as measured by Haugh units was observed in hens fed corn-soybean meal diets supplemented with brewers dried grains (Damron et al., 1976; Jensen et al., 1976), distillers feeds (Jensen et al., 1978), and corn fermentation solubles (Jensen and Maurice, 1978). The identity of the factor in these ingredients was unknown. Toepfer et al. (1973) reported that brewers yeast contained a large amount of Cr+3, which was ethanol extractable and biologically active in the rat fat pad bioassay for GTF activity.
In a earlier study, Hill and Matrone (1970) demonstrated a dietary interaction between vanadium and Cr in chicks. They observed a growth depression and high mortality in response to adding 20 ppm vanadium to the diet which were partially counteracted by adding a high level of Cr. They also demonstrated that dietary Cr partially prevented the uncoupling of oxidative phosphorylation in liver mitochondria from chicks fed vanadium. The reduction of the toxicity of vanadium by dietary Cr in chicks was confirmed by Hafez and Kratzer (1976). Jensen and Maurice (1980) later identified the factor present in distillers grains that improved the egg interior quality as Cr. They found that an equivalent increase in Haugh units may be obtained by either 10 ppm Cr or 10% distillers grains in the diet. Additionally, Cr significantly counteracted deleterious effects of vanadium on interior quality of eggs (Table 7).
These findings strongly suggest that Cr is involved in maintenance of the normal physical state of egg albumen. The possible mechanism by which Cr could work to maintain egg quality are: (1) as a structural component of egg albumen or in the cross linking of proteins, (2) Cr is necessary for the synthesis of ovomucin which is responsible for gel structure of albumen, and (3) facilitate transfer of cations (possibly magnesium) into the albumen of eggs during the plumping process in the uterus.
Anderson et al. (1989), in an attempt to identify food sources that could be enriched with Cr for human consumption, supplemented diets of turkey breeders with 25 and 100 ppm Cr from Cr chloride. Results indicated that supplemental Cr led to a significant linear increase in Cr concentration of the egg yolk but not the egg white (Table 8). Addition of 100 ppm Cr led to an approximate doubling of Cr in the egg yolk but not egg white.
Chromium concentration of the yolk was approximately 10 fold greater than that of the egg white when expressed on a wet weight basis and two to three fold greater on a dry weight basis for control eggs as well as for eggs from turkeys supplemented with either 25 or 100 ppm Cr. They also noted a reduced concentration of Cr in selected tissues of breeding turkeys receiving a basal diet without Cr supplementation. This reduced Cr concentration in the body was attributed to the stress of egg production. This fact is very important for breeder hens. Positive effects of organic Cr in increasing litter size is well documented (Lindemann et al., 1995; Campbell, 1996). The effects of supplementation of Cr on performance of breeding hens is still unknown.
Table 7. Effect of chromium, vanadium and distillers grains on interior egg quality of layers.
Table 8. Chromium concentration (ng/g) in egg white and yolk due to dietary chromium levels.*
Published data on the use of organic Cr from Cr picolinate on egg quality are scarce. Page et al. (1991) reported that 200 ppb dietary Cr from Cr picolinate in diets fed layers to 32 weeks reduced cholesterol in serum but not in egg yolk. Egg production was increased by Cr supplementation through 200 ppb but was unaffected by 400 and 800 ppb levels. Egg quality was unaffected.
In another experiment, Achee et al. (1992) found no effects of Cr on serum cholesterol or Haugh units with 18-week-old laying hens. Nakaue and Hu (1997) conducted a similar experiment with young (22 to 38 weeks) and old (75 to 91 weeks) layers using 0, 200 and 800 ppb Cr from Cr picolinate. No differences in egg production, feed conversion, Haugh units or blood triglycerides were observed in either group. In younger layers, egg cholesterol levels were significantly lower with 200 and 800 ppb Cr and in old layers Cr picolinate tended to decrease yolk cholesterol. Blood cholesterol was significantly lower only with 200 ppb Cr. It is evident from these data that supplementation of Cr represents a potential method of modifying the nutritional profile of the egg. Chromium concentration in eggs may be increased and egg cholesterol level may be reduced significantly by supplementing layer diets with organic forms of Cr.
Summary
- Trivalent Cr is biologically active in poultry and its beneficial effects include improved growth rate, feed efficiency and increased rates of lipogenesis including fatty acid and glycerol synthesis.
- Supplementation of Cr increased breast meat yield and reduced carcass fat in broilers and turkeys.
- Supplementation of Cr improved growth performance and carcass quality and reduced mortality of broilers reared under high environmental temperatures.
- Chromium supplementation offers a non-nitrogenous way to improve carcass leanness in broilers.
- Chromium increased egg albumen quality and reduced blood cholesterol in laying hens.
- Quality of poultry product can be modified or enriched by adding bioavailable forms of Cr to the diet.
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Author: SAZZAD M. HOSSAIN
Department of Animal Science, University of British Columbia, Vancouver, BC, Canada
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