Microbial Hydrolysed Feather Protein as a Source of Amino Acids and Protein in the Diets of Animals Including Poultry

Feathers are hard waste products, mainly composed of hard β-keratin, and are produced in large quantities in commercial poultry processing plants. Therefore, their industrial utilization is important economically as well as environmentally. Feathers degradation through keratinolytic microorganisms has been considered as an important method for efficient bioconversion, nutritional enhancement and eco-friendliness. The use of crude keratinase significantly increased the amino acid digestibility of raw feathers and commercial feather meal. This enzyme increased the digestibility of commercial feather meal and could replace as much as 7% of the dietary protein for growing chicks. However, feathers are currently utilized on a limited basis as a dietary protein supplement for animal feed because feather meal production is an expensive process, requiring significant amounts of energy. This review paper explains the nutritive value of feathers which makes suitable and inexpensive animal and poultry feed.


Introduction
Rising livestock is a major industry, which produces animals that have multiple uses as meat, fibers and hides. It is important to feed the stock animals a proper balanced diet, to insure optimum growth and health. Feed Industries are seeking new way to cope with raw materials costs [1]. Viable treated feather and hog hair meals have been found valuable sources of dietary protein for the growing chick [2]. Recently, supplementation of poultry diets with enzyme mixtures, including protease and amylase has produced improvements in growth performance [3]. Keratinase is an enzyme hydrolyses a broad range of protein substrate including casein, collagen, elastin and keratin [4]. Scientist reported degradation of chicken feathers and other keratinous waste materials by fungi [5] and decomposed feathers were utilized as nitrogenous fertilizers due to their high value protein content [6,7]. This feature of keratin protein can accomplish the shortage of meat raw materials and achieve desire of manufacturer to reduce production costs, and the availability of alternative sources of protein [8]. Feather degradation by microbial action seems to be a reasonable substitute to obtain feather meal that would be nutritionally raised with essential amino-acids. This line of biodegradation of chicken feathers would convert the rigid feather waste to a readily digestible feather meal.

Keratin
Keratin is hardened fiber plus matrix material which ultimately fills the cells of hair cortex. It thus consists of two main components; a fibrous protein which gives the α-keratin x-ray diffraction pattern (or the β-pattern when the polypeptide chains are extended as in feather keratin) and an amorphous protein which is termed γ-keratin [9]. Only rare microorganisms like fungi, bacteria and actinomycetes are capable to break and utilize keratin because of their hard and tough nature. Humans and other vertebrates cannot digest this macromolecule, and if eaten, it simply gets accumulated within the variety of a lump that is still undigested. A large part of tiger scat and other carnivore dung contains scleroprotein (mainly hair) aside from bones and additional complex elements which are undigestible [10]. Animal hair, hoofs, horns and wool contain β-keratin and bird's feather contains α-keratin. Keratins are also present in epithelial covering which is rich in beta helical coil linked through cysteine bridges [11]. The higher the percentage of sulfur, the higher is the stability of keratin towards solubilization [12]. The keratin proteins are compound that are extremely resistant to action of physical, chemical and biological agents. Hair, horns, nails and cornified tissue are some naturally occurring forms of keratin [13][14]. Keratin is a protein macromolecule with very high stability and low degradation rate.
Keratins are categorized into hard and soft keratins according to the sulfur content. Hard keratins have high content di-sulphide linking and are found in appendages. Soft keratins have low content of disulphide bond making skin and callus [15]. Keratins belong to the super family of IF protein. Intermediate filament proteins are planned, prolonged α-helical conformation prone to form twostranded coiled coils. The durability of keratins is a direct consequence of their complex architecture [16].

Chicken feathers
The main component of feather is keratin, a mechanically durable and chemically unreactive and insoluble protein, which render it difficult to be digested by most proteolytic enzymes. Keratin is resistant to enzymatic digestion by plant, animals and many known microbial proteases due to insoluble nature. Feathers having only 10% parts which is not keratin, rest 90% is resistant to degradation by common peptidases. This resistance is due to constituent amino acid composition and configuration that provide structural rigidity [17]. Chicken feathers are made up of over 90% of keratin protein, small amounts of lipids and water. Feathers contain about 15% N on a dry weight basis and huge quantities are produced as industrial by product. However, they have not been used effectively as plant bio fertilizers since N mineralization are slow meet plant requirements [18]. Feather waste, resulting in large quantities as by product of poultry farms processing, are pure keratin proteins.

Keratinases from microorganism
The keratinase producing micro-organisms have been discovered in several different biological groups, including fungi, bacteria and actinomycetes.

Bacterial strains
The genera Burkholderia, Chryseobacterium, Pseudomonas and Microbacterium sp. were grown on solid medium with feather meal as sole carbon and chemical elements and screened for proteolytic activity on milk agar plates [19]. Three Bacillus species were isolated from the poultry industry and evaluated for keratinase production using feathers or feather meal as the sole carbon and nitrogen sources in a submerged fermentation. B. subtilis 1273 was the strain which exhibited the highest enzymatic activity [17]. A number of keratinases producing Bacillus and Pseudomonas species have been isolated from various environmental sources such as soil farm wastes and raw feather [20]. Bacillus sp., Bacillus licheniformis, Bacillus subtilis KD-N2, Burkholderia was isolated for keratinase production [21-22].

Actinomycetes strains
Thiosulfate production from cystine by keratinolytic prokaryote Streptomyces fradiae [23]. Biochemical mechanism of keratin degradation by the actinomycete Streptomyces fradiae and the fungus Microsporum gypseum: a comparison [24]. Keratinolytic serine protease was purified and characterized from Streptomyces albidoflavus [25]. Native keratin decomposition by thermophilic Actinomycetes was studied [26]. Keratinase enzyme was isolated and characterized, which was produced during wool degradation process by Thermoactinomycetes candidus [27]. Thermoactinomycetes degraded keratin and other collagenous waste by alkaline hydrolysis [28]. A new strain of streptomyces was used to degrade feather [29]. A new actinomycetes was isolated from coastal region of south India and studied keratinase production [30].

Fungal strains
The thermophiles may be advantageous in comparison with mesophiles, because of their accelerated reaction processes and the accumulation of biomass and enzymes and diminished the risk of contamination in industrial activity. A large number of keratinases producing fungi were observed by [31]. 234 fungal strains were isolated by baiting method used for feather degradation and keratinase producing ability. Maximum clearing zone was made by Chrysosporium indicum on solid agar plates. The highest keratinase production was found in case of Acremonium strictum while Chrysosporium indicum and Chrysosporium tropicum was found next to it [32]. Fungal keratinase reported from India are listed in Table 1.

Feathers as source of proteins and amino acids
An appealing alternating method to obtain amino acids and proteins is to use feathers that are relatively stable under natural conditions. Keratinophilic fungi used to hydrolyse keratin protein to obtain protein [33] and found maximum producer as C. indicum, C. tropicum, and Malbranchea pulchella. Parihar and Kushwaha [45] used Verticillium tenuipes, Microsporum gypseum, Aphanoasus fulvescens, Chrysosporium keratinophilum for study of protein release in hen feather degradation without rachis. C. indicum was used for degradation of human hair and estimated protein release 47.66 μg/ml and 112.66 μg/ml in 5 and 10 days respectively [46]. Chrysosporium tropicum, Penicillium griseofulvum and Aphanoascus terreus was analyzed for release of considerable amount of protein [47]. [48] observed protein release 409.6 μg/ml in case of C. tropicum in 12 days while Malbranchea sp. released 298.21 μg/ml in 4 days. [46] recorded 238 μg/ml in 25 days by Alternaria tenuissima.
Conversion of feathers into feather meals by applying physical and chemical methods results in the loss of nutritionally essential amino acids such as methionine, lysine and tryptophan. Therefore, currently the poultry feathers are converted into feather meal, a digestible dietary protein, for animal feed using keratinases. The microbial production of L-lysine is an expanding branch of manufacturing biotechnology. There are many reports are available worldwide. Indian researcher [37] studied the discharge of cysteine in the culture medium.  [47] recorded cysteine produced by Acremonium strictum 32.00 μg/mL, Chrysosporium tropicum 25.00 μg/mL, Chrysosporium indicum 22.00 μg/mL, Malbranchea aurantiaca 21.00 μg/mL. [48] Studied the discharge of amino acids lysine, cysteine, methionine, valine by C. tropicum and Malbranchea sp. due to feather degradation.

Animal feed
The upgradation of feather meal through microbial or catalyst treatment has been defined earlier. Feather meal fermented with Streptomyces fradiae and supplemented with essential amino acid methionine bring about in the broilers growth rate comparable with those fed isolated soybean protein [49]. The application of feather-lysate from B. licheniformis with amino acid supplementation formed alike development rate in chickens when compared to chickens fed with a diet included with soybean meal [50]. Feather hydrolysates produced by microbial keratinases have been used as additives for animal feed [51]. The application of biotechnological approach using microbes for feather processing has nutritional significance. Culturing of the microorganisms and keratinase activity may result in modification of structure of feather keratin [4,[52][53][54]. This may alter its resistance to digestive enzymes of the consuming animals [55]. Fermentation of feathers involving microorganisms and microbial enzymes, not only it would retain the existing valuable amino acid content of keratin, but it would also add to it. Thus, the feather meal obtained after such microbial treatment would have enough nutritional value. Keratinase could play a significant role in enzymatic improvement of feather meal and amino acid production from high molecular weight substrate [56]. The microbial technology would significantly bring down the cost since it would not require hydrothermal treatment, however feather waste would be a cheap raw material [57].

Feather meal as Chick feed
Meat and feather meal protein gave equally as good results as soybean meal protein when supplied 3% protein in practical-type corn-soybean meal rations [58]. [59] observed growth of feather and composition in broiler chicken and found that that of threonine, isoleucine and valine increased with age while methionine content of feathers decreased with age. B. licheniformis produced crude keratinase enzyme augmented the total amino acid digestibility of raw feathers and commercial feather meal, could replace as much as 7% of the dietary protein for growing chicks [19]. [60] Studied dietary crude protein and lysine amino acid effect on growth of feather in chicks and found that crude protein has more influence on feather development than by levels of lysine. [61] Observed antioxidant potential property of protein hydrolysate developed by Bacillus sp. [62] observed replacement of fish meal with feather meal in broiler and found economic without any negative effect. Treated chicken feather meal used as a source of protein ton animal feed broiler chickens [63]. [64] Observed processed feather meal for their chemical composition and amino acid profile and found feather meal pre-soaked with wood ash for twentyfour hour boiled at 150°C for 1 hr. gave the best crude protein content. Using feather waste as a valuable resource can help the poultry industry to dispose of the waste feathers in an environmentally sustainable manner that also generates extra income for the industry [65]. [66] Improved digestibility of protein into feather meal by

Author details
Jitendra Kumar Department of Botany, Dolphin PG College of Science and Agriculture, Fatehgarh Sahib, Punjab, India *Address all correspondence to: jeetmicro@gmail.com enzymatic treatment. Feather meal can be included in the broilers diet without any negative effect on its performance [67]. [68] Studied effect of hydrolysed feather meal on feed efficiency, survival rate and carcass composition of red tilapia.

Conclusion
Microbial keratinase substances improve keratin protein hydrolysis and increases nutritive value of feather meal. Microbial hydrolysed protein is rich in essential amino acid contents and other oligopeptides which are good and cheap for poultry feed. Supplementary learning outcome is desirable in an integrated sustainable approach to solve environmental issue of keratinous solid waste management and provide cheap and healthy feed.
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[6] Kumari M, Kumar J. Chicken feather waste degradation by Alternaria tenuissima and its application on plant growth. Journal of Applied and Natural Sciences.2020; 12 (3)