INTRODUCTION
Chromium (Cr) is an essential mineral which was first demonstrated by Schwarz and Mertz in rats and by Jeejebhoy, et al., (1977) in humans. Over the recent couple of decades, Cr has been considered to play a vital role in livestock and poultry production. Cr is not only an essential micromineral required for protein, lipid, carbohydrate and nucleic acid metabolism, but also additionally activates certain enzyme system and stabilizes protein. Cr is one of the transition elements and occurs in valancies of two, three and six. The hexavalent form is a known toxin, mutagen, and carcinogen. Cr is most stable in trivalent state (Cr+3) which is the only physiologically active form of the element. Organic sources of Cr are ten times more bioavailable than inorganic sources. It was reported that chromium propionate is absorbed more efficiently than few other organic Cr sources. The beneficial effects of chromium propionate in poultry health and nutrition is discussed as follows.
METABOLISM OF CHROMIUM
The principal route by which trivalent chromium enters the body is through the digestive system. Absorbed chromium circulates as free trivalent Cr, because it is bound to transferrin or other plasma proteins, or as complexes such as glucose tolerance factor (GTF). Circulating trivalent Cr is taken up by tissue and its distribution in the body depends on age and chemical form. The dietary sources influencing Cr absorption from the gut include amino acids, ascorbic acid and oxalates. Organic Cr gets absorbed in better way into the gut as compared to inorganic Cr salt and thus has higher bioavailability. Inorganic Cr binds irreversible to the undigested material in the intestines and their absorption is reduced from the small intestine. The reasons of lower bioavailability of inorganic Cr are numerous and they are likely to be relating to the formation of non-soluble Cr oxides, Cr binding to natural chelate-forming compounds in feed raw materials, interference with ion forms of other minerals (Zn, Fe, V) and the slow conversion of inorganic Cr to the bioactive form. The absorption of Cr in the gut is enhanced by ascorbic acid by chelate formations, which prevents its precipitation at the alkaline pH of poultry gut. It is excreted primarily in the urine by glomerular filtration or bound to a low molecular weight organic transporter.
EFFECT ON METABOLISM AND DIGESTION OF NUTRIENTS
Chromium is an essential trace mineral involved in carbohydrate, protein and lipid metabolism. Cr is biologically active part of a biomolecule called chromodulin, which is part of an insulin signaling pathway thus affecting carbohydrate, protein and lipid metabolism. Cr is known to enhance the insulin sensitivity and reduce the plasma glucose concentration in broilers. Insulin controls the metabolism of carbohydrate, protein, lipid and stimulates the uptake of amino acids, protein synthesis and glucose utilization. Cr supplementation has reduced plasma glucose and non-steroid fatty acid concentration in broilers. Promoting glycogen and fatty acid synthesis are well documented effects of insulin. Cr acts as a cofactor of insulin activity and the presence of this mineral is required for proper glucose metabolism and growth in animals. Many studies supported that Cr supplementation in poultry diet decreased serum glucose level and it is proven that Cr is necessary mineral for normal glucose metabolism. Supplementation of chromium propionate in male broiler reduced the broiler serum glucose levels and increased the total protein levels. Cr supplemented diet increased serum insulin, decreased corticosterone level and glucose concentration in laying hens. The supplementation of Cr in poultry diet may enhance the utilization of dietary energy through stimulation of insulin action and thus could help to maintain the productivity of birds even if the dietary energy level is low.
Chromium may exert a protective effect on pancreatic tissue which results in an increased pancreatic function comprising of the release of digestive enzymes and enhanced nutrient digestion. Cr supplementation increased the digestibility of dry matter, ash, organic matter, crude protein, crude fiber and ether extract in laying hens.
EFFECT ON GOWTH PERFORMANCE AND FEED EFFICIENCY
Several studies suggested that supplementation of Cr at different dose levels in poultry diet improved feed efficiency, live weight gain and carcass quality. Supplementation of Cr at 500 μg/kg in broiler diet improved their body weight gain and feed efficiency during the growing phase. Cr supplementation in poultry diet showed better performance during heat stress. It was suggested that 0.5 mg/kg of Cr helps in improving the feed efficiency and carcass quality. An improvement of both final live weight and total live weight in Cr supplemented diet was observed in broilers. Supplementation of chromium propionate in broiler diet showed better breast meat yield. It was also reported that chromium propionate supplemented diet improved the feed efficiency and reduced the mortality in broiler.
EFFECT ON LAYING HENS PERFORMANCE
Dietary supplementation of Cr in the diet of laying hens enhanced production performances and egg quality. Inclusion of Cr at the rate of 400 and 800 μg kg-1 of feed in laying hens improved their egg weight, specific gravity, shell thickness and Haugh unit. Addition of chromium propionate at a dose level of 400 μg kg-1 of feed improved egg production, while 600 μg kg-1 improved egg shell thickness in late-phase laying hens. Cr supplementation improved feed efficiency and egg production in laying hens. Also, Cr addition at a dose level of 1200 ppb increased the production performance, egg quality and serum insulin level of laying Japanese quails.
EFFECT ON ENVIRONMENTAL STRESS IN POULTRY
Environmental stress causes adverse effects on feed intake, nutrient digestibility, feed efficiency and egg production in poultry. Plasma corticosterone concentration also increases during stress. Corticosterone acts as an antagonist to insulin activity, reduces the glucose utilization by peripheral tissues and causes stress-induced hyperglycemia in poultry. Corticosteroid also reduces the plasma protein and increases blood glucose concentration. Heat stress decreases the serum vitamin and mineral concentration in poultry. Chromium stimulate and regulate the action of insulin which is involved in anabolic processes. A plenty of literature reported that dietary Cr requirement of poultry was significantly affected by environmental stress and negative effects of stress were prevented by Cr supplementation. Inclusion of dietary Cr in poultry diet improved the growth rate and feed efficiency. These beneficial effects of Cr can be observed more efficiently under environmental, dietary and hormonal stress.
EFFECT ON IMMUNE HEALTH
One of the important role of Cr is to stimulate the immune function. The immune function may be affected in association with corticosteroids activity, but it can be mediated by production and regulation of certain cytokines. Cr is believed to have different kinds of humoral and cell mediated immunomodulatory effect. Chromium propionate supplementation improved the antibody response of broiler to vaccination against new castle disease. A positive response to new castle disease virus in broiler chicks induced to heat stress was observed when supplemented with organic chromium. Organic Cr was found to be better in reducing heat stress related immune suppression in broiler chicks. It was suggested that supplementation of chromium propionate at different dosage levels (100-3200 μg kg-1) gives significant benefits in terms of improved humoral and cell mediated immune response. However, the increased dose of chromium propionate, antibody response against new castle disease vaccination and cell mediated immune response enhanced quadratically. In broiler chickens, addition of chromium propionate in drinking water or feed improves the immune responses through up-regulating interferon-gamma (IFN-γ) expression after vaccination with R2B strain of newcastle disease (ND).
CONCLUSION
Chromium is an essential trace mineral that plays an important role in poultry nutrition and health. Chromium is used in poultry diet because of its anti-stress effects, various nutritional and immune enhancing effects. Chromium propionate has beneficial impacts on metabolism of nutrient, growth performance, feed efficiency and immune health in poultry. Moreover, it is very helpful in stressed condition. The chromium requirement of various species of poultry are the areas that warrant attention.
by Anjan Mondal, Kemin Industries South Asia Pvt. Ltd
