Valuable byproducts are obtained from slaughtering of meat animals and used for various purposes by mankind. From anti-aging creams to surgical sutures, skin grafting and xenotransplantation to chocolate milkshakes, ice-creams and marshmallows we have used animal products from cattle, sheep and hogs into nearly every corner of our lives. Slaughtering and processing of meat animals can only harvest one third of its weight as meat but the rest comprises of byproducts and waste which ranges from 50-60% of the live weight. BAH & FS, Government of India (2017) estimated that about 165 million livestock and 2300 million poultry birds were slaughtered during 2016-17 in India owing to production of 7.4 million tones of meat. It leaves huge loads of byproducts which were also contributed by dead and fallen animals. It accounts for more than 10 million MT of edible and inedible by-products. The animal by-products are categorized mainly into edible and inedible by-products. On the basis of live weight of animal the by-products account for almost 60%, of which 40% are edible and 20% are inedible (Chatli et al., 2005). Another basis for classification of animal by- products is their ultimate use. These include agricultural byproducts (meat meal, bone meal, fertilizer etc.); industrial byproducts (gelatine, glue, casings etc.) and pharmaceutical byproducts (insulin, pepsin, biochemicals, hormones etc.) (Sharma, 2011). The therapeutic value of most meat byproducts are exploited for use in human healthcare.

The art of treating human ailments by using therapeutics derived from animal origin is known as zootherapy (Costa-Neto, 2005). As Marques (1994) states, “all human culture which presents a structured medical system will utilize animals as medicines”. By-products obtained from wild and domestic animals (e.g., hooves, hides/skins, bones, feathers, tusks etc.) form important ingredients in the curative, protective and preventive medicine (Adeola, 1992). The World Health Organization (WHO) estimates that as many as 80% of the world’s more than six billion people rely primarily on animal and plant-based medicines. Animals have been methodically tested by pharmaceutical companies as sources of drugs for modern medical science (Kunin et al., 1996), and the current percentage of animal sources for producing essential medicines is quite significant. Of the 252 essential chemicals that have been selected by the World Health Organization, 8.7% come from animals and of the 150 prescription drugs currently in use in the United States of America, 27 have animal origin (WRI, 2000). Current experiments in xenotransplantation most often use pigs as the donor, and baboons as human models.

Nutritive Value of Edible By-Products

Edible meat by-products contain many essential nutrients. Some are used as medicines because they contain special nutrients such as amino acids, hormones, minerals, vitamins and fatty acids. Various meat by-products have a higher level of moisture than meat. Some examples are blood, skin, lung, kidney, brains, spleen, and tripe. Some organ meat, including liver and kidney, contains a higher level of carbohydrate than other meat materials (Devatkal et al., 2004b). Highest fat content and the lowest moisture content of all meat by-products are found in pork tail. The liver, tail, ears and feet of cattle have a protein level which is close to that of lean meat tissue, but a large amount of collagen is found in the ears and feet (Unsal and Aktas, 2003). The amino acid composition of meat by-products is different from that of lean tissue, because of the large amount of connective tissue. As a result, by-products such as ears, feet, lungs, stomach and tripe contain a larger amount of proline, hydroxyproline and glycine, and a lower level of tryptophan and tyrosine. The organ meat contains higher amount of vitamins than lean meat tissue. Kidney and liver contain the largest amount of riboflavin (1.697–3.630 mg/100 g), and have 5–10 times more than lean meat. Liver is the best source of niacin, vitamin B12, B6, folacin, ascorbic acid and vitamin A. Kidney is also a good source of vitamin B-complex. A 100 g serving of liver from pork or beef contributes (450–1,100) % of the RDA of vitamin A, 65% of the RDA of vitamin B6, 3,700% of the RDA of vitamin B12 and 37% of the RDA of ascorbic acid. Lamb kidneys, pork, liver, lungs, and spleen are an excellent source of iron, as well as vitamins. The copper content is highest in the livers of beef, lamb and veal. They contribute 90–350% of the RDA of copper (2 mg/day). Livers also contain the highest amount of manganese (0.128–0.344 mg/100 g). However, the highest level of phosphorus (393–558 mg/100 g) and potassium (360–433 mg/100 g) in meat by-products is found in the thymus and sweetbreads (Devatkal et al., 2004). With the exception of brain, kidney, lungs, spleen and ears, most other by-products contain sodium at or below the levels found in lean tissue. Mechanically deboned meat has the highest calcium content (315–485 mg/100 g).

Many organ meats contain more polyunsaturated fatty acids than lean tissue. Brain, chitterlings, heart, kidney, liver and lungs have the lowest level of monounsaturated fatty acids and the highest level of polyunsaturated fatty acids (Liu, 2002). Brain is the highest in cholesterol (1352 to 2195 mg/100 g) and also has the highest amount of phospholipid when compared with other meat by-products. In the past, by products were a favorite food in Asia, but in present situation there is an increased focus on non-food uses, such as pet foods, pharmaceuticals, cosmetics and animal feed (Rivera et al., 2000).

By-products in Human Healthcare

Slaughtered animals are the source of general medical and health care products which include antibodies (immunoglobins), beef insulin, bovine collagen (used as injections to fill in scars), bovine fibrinolysin ointment for necrotic tissue, bovine super oxide dismutase cosmetic skin cream to prevent tissue aging), bovine thrombin- clotting agent for blood, culture medium for diagnosis, fetal bovine serum for tissue cultures, hyaluronidase (for efficient drug use), PTH (controls tetany), Pegademase – bovine derivative for patients who are immuno-compromised and helps prevent white blood cells from breaking down, gelatin pills/capsules, whole serum (vaccine manufacturing) etc.

1. Blood

Blood can be separated into several fractions that have therapeutic properties. Liquid plasma is the largest fraction (63.0%). It consists of albumin (3.5%), globulin and fibrinogen (4.0%). In the laboratory, many blood products are used as a nutrient for tissue culture media, as a necessary ingredient in blood agar, and as peptones for microbial use (Kurbanoglu and Kurbanoglu, 2004). Purified bovine albumin is used to help replenish blood or fluid loss in animals. It is used in testing for the Rh factor in human beings, and as a stabilizer for vaccines. It is also used in antibiotic sensitivity tests. Superoxide dismutase (SOD) enzyme can be extracted from cattle and porcine blood for curing osteoarthritis, ischemia and in anti-inflammatory treatment and so forth (Hass et al., 1993).

1. Arteries

Bovine carotid arteries (DeFalco, 1970) up to 55 cm (21.7 in) in length and 9­11 mm (0.35­0.43 in) in diameter may be treated with an enzyme (to remove parenchymatous immunologically reactive proteins), subsequently tanned (makes collagen stronger and more nonreactive) and then sterilized for later implantation into humans as a femoropopliteal or iliofemoral substitute.

• Hide and Skin

1. Gelatin

Gelatin extracted from animal skins and hides can be used for food (Choa et al., 2005). Approximately 6.5% of the total production of gelatin is used in the pharmaceutical industry (Hidaka and Liu, 2003). Most of it is used to make the outer covering of capsules. Gelatin can also be used as a binding and compounding agent in the manufacture of medicated tablets and pastilles. It is used as an important ingredient in protective ointment, such as zinc gelatin for the treatment of ulcerated varicose veins. Gelatin can be made into a sterile sponge by whipping it into foam, treating it with formaldehyde and drying it (Estaca et al., 2009). Such sponges are used in surgery, and also to implant a drug or antibiotic directly into a specific area. Gelatin is an excellent emulsifier and stabilizing agent for many emulsions and foams. It is used in cosmetic products, and in printing for silk screen printing, photogravure printing etc. (Arvanitoyannis, 2002). A product made from extracted collagen can stimulate blood clotting during surgery.

1. Skin Grafting

Pork skin is similar to human skin, and can be converted into a graft/dressing for burns or skin-ulcers.

1. Bone

Cartilage

Specifically processed xiphoid or xiphisternal cartilage from the breastbone cartilage of young cattle is used by plastic surgeons to replace facial bone.

Collagen

Unmodified collagen from demineralized bone powder is used for packing holes in gums and bones and is used as standards in diagnostic kits (Slim, 1997).

Gelatin from Bone

Ossein is normally produced from bone for gelatin extraction and gelatin extracted has same use as that extracted from hide and skin.

Bone Meal

Bone meal is also a nutritional source of calcium (averages 23%) and phosphorus (averages 12%) in the diet. Steamed bone meal has had most of the protein and fat removed and contains approximately 32.5% calcium and 15.1% phosphorus. If ground sufficiently fine, bone can be added to milk to increase the calcium level. Bone meal is also used as a filtering agent in water purification systems.

Bone Marrow

Marrow, marrow extract or red bone marrow, bone powder, and bone ash (approximately 15.3­16.6% phosphorus) products are also available as human and animal dietary supplements. Red bone marrow is used to treat patients who have a low red blood cell count. It can be fed orally and is stable to heat and the action of the digestive juices.

1. Glands and Organs: Medicinal and Pharmaceutical Uses

Animal glands and organs are traditionally used as medicine in many countries, including China, India and Japan.

1. Brain, Nervous System and Spinal Cord

Brains, nervous systems and spinal cords are a source of cholesterol which is the raw material for the synthesis of Vitamin D₃. Cholesterol is also used as an emulsifier in cosmetics (Ejike and Emmanuel, 2009) and anti-aging creams.

1. Trachea

The trachea is used as a source of collagen and GAGs. The trachea also contains a trypsin inhibitor (aprotinin) and is sold as a biochemical reagent and has potential therapeutic value.

1. Lungs

Heparin (mucopolysaccharide), an anticoagulant that prolongs the clotting time of blood, is used to prevent blood clots and can be extracted from the lungs, the liver,  or the intestine mucosa (usually pig and beef). It is being used in “minidoses” in the prevention of postsurgical pulmonary emboli by blocking coagulation of blood in the intact blood vessel. Heparin is also used to prevent gangrene in frostbite and as a burn treatment. Lungs also contain aprotinin, a trypsin inhibitor that is used as a biochemical reagent and has potential therapeutic value.

1. Heart

Heart valves from young to market weight pigs are preserved and treated (converted to a “biological plastic”) prior to surgical implantation into the human heart in  place of a defective valve (often caused by rheumatic fever or birth defects). The pig heart valve (xenograft) is often preferred over a mechanical valve, which requires constant infusion of anticoagulant (blood thinning) drugs to prevent the blood from forming clots on the valve (causing sudden malfunction) or free floating thromboemboli (causing stroke or paralysis). If a problem develops with a hog valve, malfunction is usually not fatal because (as with a natural valve) early warning symptoms alert the patient in time for reoperation.

Pericardial tissue (membrane enclosing and attaching the heart in the thoracic cavity) from beef animals is also cleaned, glutaraldehyde­processed, and used to repair or replace the patient’s own pericardial tissue after heart surgery. Use of this pericardial patch prevents the adhesion of the patient’s myocardium to the sternum following surgery.

1. Glands

The endocrine glands secrete hormones and enzymes that regulate the body’s metabolism. These include the liver, pituitary, thyroid, pancreas, stomach, parathyroid, adrenal, corpus luteum, ovary and testes. The glands are collected only from healthy animals.

Table1: General Medical and Health Care Products from Animal Glands (Okerman, 2000)

1. Spleen

The spleen is often collected from beef and pork carcasses for pharmaceutical use. The spleen (largest structure in lymphoid system) extract (splenin fluid) influences capillary permeability, recovery from inflammation (redness and swelling) and blood-clotting time. Spleen extract is also used to treat certain blood and lymph diseases. It is marketed as powder, tablets and capsules.

1. Animal Intestines

The intestines of sheep and calves are used for the manufacture of catgut, to make internal surgical sutures. The lining of the small intestines of pigs and cattle are being processed into casings. It is either preserved in a raw state, or processed into a dry powder for heparin manufacture.

1. Horns and Hooves

Keratin from horns has been proposed as a hair care unit. Powdered horn and the velvet from deer horns is used as an aphrodisiac supplement in Asia (Slim, 1997).These are also used for manufacturing adhesives, bandage strips, collagen cold cream, cellophane wrap and tape, crochet needles etc.

vii. Animal Fats and Fatty Acids

Used in manufacture of chewing gum, pharmaceuticals, animal foods, biodegradable detergents, biodiesel, cellophane, cement, ceramics, cosmetics, glycerin, glycerol, antifreeze, lubricants, medicines, ointment bases, plasticizers, hair conditioner/shampoo, soaps etc.

• Glycosaminoglycans (GAGs)

The sources and usage of various GAGs found in animal body are given as follows:

Table 2: Use of glycosaminoglacans from animals (Slim, 1997)

Hyaluronic acid can be extracted from the corium of the eyes and is used as a packing material in eye surgery. The more preferred product is extracted from rooster combs. It is also used in cosmetics as a moisturizing agent.  GAGs are also sold as health food, cosmetic moisturizer, and to add “feel” to creams. Other reported uses are as stock feed and as a treatment for arthritis. They can be isolated from cartilage and trachea. Heparin is another GAG that is used to prevent blood coagulation. To date, the isolation is still totally from natural sources.

1. Bioactive Peptides

Meat trimmings, mechanically recovered meat, collagen, blood are rich source of proteins and hence constitute an ideal substrate for proteolysis. These proteins are subject to hydrolysis with specific commercial proteases and are known to have antihypertensive, antimicrobial, anti-obesity, antioxidant activities hence used in various functional/ healthy food preparations (Table 3). In vaccine production and in microbiological culture medium, meat peptone is used as a source of nutrient. Collagen hydrolysate obtained from bovine trachea is used in arthritis (a nutraceutical) and in cosmetics (shampoos and skin creams).

Table 3: Antihypertensive peptides derived from animal by-products

1. Wool

Wool grease contains 15% cholesterol. The oil glands of sheep are the source of lanolin. Some ophthalmic drugs contain lanolin as an ingredient. It is used as a carrier in certain drugs that are injected to body. Lanolin is also is found in eye drops because it has antibacterial properties and can protect against dry eyes.

Conclusion

By-products from the meat industry are rich sources of many fine chemical and biochemical extracts needed in the pharmaceutical, food and cosmetic industries. Some of the classes of material which can be extracted from meat industry by-products and are having therapeutic value for human healthcare are – steroids, polysaccharides, proteins, thymus extracts, hormones etc. Meat producers have, for a long time, efficiently used meat by-products in processing into either edible or inedible products. Today, with increasing concerns about health and environmental protection, many new techniques, operating procedures, and research have been developed to permit more efficient processing and utilization of these by-products. Contributions and efforts are also necessary for the meat industries to change in an innovative manner and to widen the opportunities to utilize meat by-products. Furthermore, although the development of synthetic substitutes in the middle of the 20^th century decreased the value of many animal byproducts, but their importance in the pet food industry and the medical/veterinary field are contributing to an increase in byproduct values in recent years. However, the saying “the packer uses everything but the squeal” has always existed in the meat industry and will continue to influence the utilization of meat byproducts.

Acknowledgement

The authors would like to acknowledge Dr. Subhasish Biswas, Professor & Head, Department of LPT, WBUAFS, Kolkata for his valuable inputs in preparing this manuscript.

Conflict of Interest

There is no conflict of interest to disclose.

References

1. Adeola, M. O. (1992). Importance of wild Animals and their parts in the culture, religious festivals, and traditional medicine, of Nigeria. Environmental Conservation, 19, 125–134.
2. Arvanitoyannis, I. S. (2002). Formation and properties of collagen and gelatin films and coatings. In: A. Gennadios, A. (Ed.) Protein-based films and coatings.Boca Raton: CRC Press Lancaster EUA, 2002. p. 275-304.
3. BAH & FS. (2017). Basic animal husbandry & fisheries statistics Annual Report – 2017, Government of India, Ministry of Agriculture & Farmers welfare, Department of Animal Husbandry, Dairying and Fisheries.
4. Banerjee, P. and Shanthi, C. (2012). Isolation of novel bioactive regions from bovine Achilles tendon collagen having angiotensin I-converting enzyme-inhibitory properties. Process Biochemistry, 47(12), 2335–2346.
5. Bernardini, R., Mullen, A. M., Bolton, D., Kerry, J., O’Neill, E., Hayes, M. (2012). Assessment of the angiotensin-I-converting enzyme (ACE-I) inhibitory and antioxidant activities of hydrolysates of bovine brisket sarcoplasmic proteins produced by papain and characterisation of associated bioactive peptidic fractions. Meat Sci. 90, 226–235.
6. Byun, H. G., and Kim, S. K. (2001). Purification and characterization of angiotensin I converting enzyme (ACE) inhibitory peptides from Alaska pollack (Theragra chalcogramma) skin. Process Biochemistry, 36, 1155-1162.
7. Chang, C. Y., Wu, K. C., and Chiang, S. H. (2007). Antioxidant properties and protein compositions of porcine haemoglobin hydrolysates. Food Chem. 100(4), 1537–1543.
8. Chatli, M. K., Padda, G. S. and Devatkal, S. K. (2005). Augmentation of animal By-products processing for the sustainability of meat industry, Indian Food Indust. 24(5), 69-73.
9. Choa, S. M., Gub, Y. S. and Kima, S. B. (2005). Extracting optimization and physical properties of yellow fin tuna (Thunnus albacares) skin gelatin compared to mammalian gelatins. Food Hydrocolloids, 19(2), 221–229.
10. Costa-Neto, E. M. (2005). Animal-based medicines: biological prospection and the sustainable use of zootherapeutic resources. An Acad Bras Cienc, 77, 33–43.
11. Daoud, R., Dubois, V., Bors-Dodita, L., Nedjar-Arroume, N., Krier, F., Chihib, N. E., Mary, P., Kouach, M., Briand, G., and Guillochon, D. (2005). New antibacterial peptide derived from bovine hemoglobin. Peptides, 26(5), 713–719.
12. DeFalco, R J. (1970). Immunological studies of untreated and chemically modified bovine carotid arteries. Surg. Res,. 10, 95­100.
13. Devatkal, S, Mendiratta, S. K., Kondaiah, N., Sharma, M. C. and Anjaneyulu, A. S. R. (2004). Physicochemical, functional and microbiological quality of buffalo liver. Meat Sci. 68(5), 79–86.
14. Ejike, C. E. C. C. and Emmanuel, T. N. (2009). Cholesterol concentration in different parts of bovine meat sold in Nsukka, Nigeria: Implications for cardiovascular disease risk. African Journal of Biochemistry Research, 3(4), 95-97.
15. Estaca, J. G., Montero, P. F., Martín, F. and Gómez-Guillén, M. C. (2009). Physico-chemical and film-forming properties of bovine-hide and tuna-skin gelatin: a comparative study. J Food Eng. 90(3), 480–486.
16. Hass, A. and Brehm, K. (1993). Superoxide dismutases and catalases—biochemistry, molecular biology and some biomedical aspects. The Genetic Engineer Biotechnologist. 13(4), 243–269.
17. Herregods, G., Van Camp, J., Morel, N., Ghesquière, B., Gevaert, K., Vercruysse, L. (2011). Angiotensin I-converting enzyme inhibitory activity of gelatin hydrolysates and identification of bioactive peptides. Journal of Agricultural and Food Chemistry, 59, 552–558.
18. Hidaka, S and Liu, S. Y. (2003). Effects of gelatins on calcium phosphate precipitation: A possible application for distinguishing bovine bone gelatin from porcine skin gelatin. Journal of Food Composition and Analysis 16(4), 477-483.
19. Hu, J., Xu, M., Hang, B., Wang, L., Wang, Q., Chen, J., Song, T., Fu, D., Wang, Z., Wang, S. and Liu, X. (2011). Isolation and characterization of an antimicrobial peptide from bovine hemoglobin α-subunit. World Journal of Microbiology and Biotechnology, 27(4), 767–771.
20. Ichimura, T., Yamanaka, A., Otsuka, T., Yamashita, E. and Maruyama, S. (2009). Antihypertensive effect of enzymatic hydrolysate of collagen and Gly-Pro in spontaneously hypertensive rats. Bioscience, Biotechnology and Biochemistry, 73, 2317-2319.
21. Inoue, N., Hamasaki, A., Hidaka, S., Miura, N., Fukahori, M., Maruyama, M., Kawahara, S., Ohta, K.. and Muguruma, M. (2013). Analysis of the components of porcine liver hydrolysate and examination of the antioxidant activity and angiotensin converting enzyme (ACE)-inhibiting activity. Yakugaku Zasshi, 133(1), 107–115.
22. Kim, S. K., Byun, H. G., Park, P. J., and Shahidi, F. (2001). Angiotensin I converting enzyme inhibitory peptides purified from bovine skin gelatin hydrolysate. Journal of Agricultural and Food Chemistry, 49(6), 2992-2997.
23. Kunin, W. E. and Lawton, J. H. (1996). Does biodiversity matter? Evaluating the case for conserving species. In: Gaston KJ, editor. Biodiversity: A biology of numbers and differences. Oxford: Blackwell Science. pp. 283–308.
24. Kurbanoglu, E. B. and Kurbanoglu, N. I. (2004). Utilization as peptone for glycerol production of ram horn waste with a new process. Energy Convers Manage. 45(2), 225–234.
25. Liu, D. C. (2002). Better utilization of by-products from the meat industry 2002-10-01. Extension Bulletins. Food and fertilizer Technology Center for the Asian and Pacific region (FFTC publication database)
26. Liu, R., Wang, M., Duan, J., Guo, J. and Tang, Y. (2010). Purification and identification of three novel antioxidant peptides from Cornu Bubali (water buffalo horn). Peptides, 31(5), 786–793.
27. Marques J. G. W. (1994). A fauna medicinal dos índios Kuna de San Blas (Panamá) e a hipótese da universalidade zooterapica. Proceedings of the Anais da 46a Reunião Anual da SBPC, Vitória, Brazil
28. Nakade, K., Kamishima, R., Inoue, Y., Ahhmed, A., Kawahara, S., Nakayama, T., et al. (2008). Identification of an antihypertensive peptide derived from chicken bone extract. Animal Science Journal, 79, 710-715.
29. Nedjar-Arroume, N., Dubois-Delval, V., Miloudi, K., Daoud, R., Krier, F., Kouach, M., Briand, G. and Guillochon, D. (2006). Isolation and characterization of four antibacterial peptides from bovine hemoglobin. Peptides, 27(9), 2082-2089.
30. Nedjar-Arroume, N., Dubois-Delval, V., Adje, E. Y., Traisnel, J., Krier, F.,Mary, P., Kouach,M., Briand, G. and Guillochon, D. (2008). Bovine hemoglobin: An attractive source of antibacterial peptides. Peptides, 29(6), 969–977.
31. Ockerman, H. W. and Hansen, C. L. (2000). Animal by-product processing and utilization. Boca Raton: CRC Press.
32. Rivera, J. A., Sebranek, J. G., Rust, R. E. and Tabatabai, L. B. (2000). Composition and protein fractions of different meat by-products used for pet food compared with mechanically separated chicken (MSC), Meat Sci., 55(5), 53–59.
33. Saiga, A., Iwai, K., Hayakawa, T., Takahata, Y., Kitamura, S., Nishimura, T., et al. (2008). Angiotensin I-converting enzyme-inhibitory peptides obtained from chicken collagen hydrolysate. J Agri Food Chem, 56, 9586–9591.
34. Sharma, B. D. and Sharma, K. (2011). Outlines of Meat Science and Technology, Jaypee Brothers Med. Publ., (p) Ltd. Pp. 360
35. Slim, G. (1997). Meat coproduct processing: from the mundane to the exotic. 43^rd ICOMST Congress Proceedings, Auckland, New Zealand, P­26, pp. 158­162.
36. Unsal, M. and Aktas, N. (2003). Fractionation and characterization of edible sheep tail fat. Meat Sci. 63(4), 235–239.
37. World Resources Institute. (2000). World Resources Report 2000–2001 People and ecosystems the fraying web of life. Washington D.C.: World Resources Institute. p. 389.
38. Yu, Y., Hu, J. N., Miyaguchi, Y. J., Bai, X. F., Du, Y. G., and Lin, B. C. (2006). Isolation and characterization of angiotensin I-converting enzyme inhibitory peptides derived from porcine hemoglobin. Peptides, 27(11), 2950–2956.