PORK AND PORK QUALITY                             PIH-128


                          Pork By-Products

John R. Romans, South Dakota State University
William J. Costello, South Dakota State University
James F. Price, Michigan State University
Richard C. Waldman, Austin, Minnesota

Tom R. Carr, University of Illinois
Frank and Barbara Essner, Chaffee, Missouri
Robert Kauffman, University of Wisconsin
Miriam and John Lewis, Walstonburg, North Carolina

     Mr. Tony  Javurek,  who  guided  two  tours  daily  at  John
Morrell's  Sioux  Falls  packing  plant  for  more than 20 years,
expressed the meat industry philosophy about  by-products  during
each tour. Tony always said, ``We use all parts of the pig except
the squeal and the curl in its tail.'' This practice  took  place
during prehistoric times when men and women used animal skins for
clothing and shelter, bones and  horns  for  tools,  tendons  and
intestines for weapons, tools, and bindings; teeth, claws, feath-
ers, and hair for ornaments; and  skins  for  containers.  Modern
society  learned  well  from  their  ancestors, and, as a result,
today's meat industry utilizes many of the nonmuscle portions  of

     Meat slaughter by-products (offal) include all parts of  the
animal that are not a part of the carcass. Cutting and processing
of the carcass result in nonmuscle by-products such as fat, bone,
and  other  connective tissues. Processed by-products have been a
significant source of income to the meat processing industry. The
United  States Department of Agriculture (USDA) Economic Research
Service (ERS) (1990) reported the portion of gross farm value  of
swine  attributable  to  edible and inedible pork by-products for
the years 1985 to 1990 ranged from  5.6%  to  6.3%  and  averaged
6.0%. Thus, if hogs are selling for $50 per hundred weight (cwt),
$6.90 of the value of a 230-pound hog represents the worth of the
by-products ($50 x 2.3 cwt x 6% = $6.90). Many different products
and their predominant use are  listed  throughout  the  remaining
pages of this fact sheet. However, at times market conditions and
alternate product availability preclude the use which  is  listed
in which case the item is used in a lower valued product.

     The use of by-products is a controversial subject. One  seg-
ment  of society values the many products made available from by-
products. There is, however, another point  of  view.  There  are
concerns  about  the  environment  and  the related energy costs.
These concerns have made the use of by-products a major  economic
and  management  problem for the meat industry. Today, economics,
modern technology, and the industry's concern for the environment
result  in  maximum  salvage  and  utilization  of all by-product
materials. A hog kill operation with a 1,000-head-per hour  capa-
city  must  be able to process approximately 72,000 pounds of by-
product material per hour. In many communities, the air and water
effluent  (flowing out) from meat operations must be as clean, or
cleaner, than the water and air entering the plant.

Edible By-Products

     Edible by-products,  oftentimes  referred  to  as  ``variety
meats,''  are  listed  alphabetically  in Table 1. The yields are
based on a 230-pound hog along with a brief  description  of  the
use  of  each  by-product.  Prices  for  these edible by-products
change, depending on their use and availability.  Current  prices
are available from the following sources:

The Yellow Sheet, Daily Market and News Service,  published  five
days weekly by:
The National Provisioner
15 West Huron Street
Chicago, IL 60610
Phone: (312) 944-3380

The Meat Sheet, published five days weekly by:
Meat Research and Reporting Service
643 South Route 83
Elmhurst, IL 60126
Phone: (312) 963-2252

Market News, published weekly and the Blue Sheet  published  five
days weekly by:
U.S. Department of Agriculture
Agricultural Marketing Service
Livestock & Grain Market News, Room 2623-S
P.O. Box 96456
Washington, D.C. 20090-6456

     Your state probably has a livestock  and  meat  market  news
publication that is available to residents.

     When you have interest in computing the value of  these  by-
products, you can use the yield factors in Table 1 and the prices
from your most readily available source.  The nutritive value  of
selected by-products is listed in Table 2.

Table 1.  Edible pork by- products yields and uses from a 230- pound
market hog (cont.).

By-product  Wt. (lb.)                     Uses
Blood       7.0      According to the United States Department of  
                     Agriculture Food Safety and Inspection Service,
                     no blood which comes in contact with the surface
                     of the body of an animal or is otherwise contam-
                     inated can be used for food purposes. Only blood
                     from inspected animals may be used for meat food
                     products. In Europe, blood proteins are utilized  
                     in food to a greater degree than they are in the  
                     USA. Collection systems for blood have been dev-
                     eloped in Europe which utilize cannula-like fun-
                     nel devices for blood removal and some draw the  
                     blood directly from the animal's vascular system  
                     into sterilized, vacuumized containers. Blood is  
                     used in many different sausage formulations and  
                     in new cake mixes.

Brains      0.25     Sold in domestic and foreign markets. It is slic-
                     ed thinly, breaded, and deep fat fried. Alternat-
                     ely broken into small pieces and mixed with eggs.

Chitterlings         Large and/or small intestines. Preferred quality  
                     comes from the middle 2.5 yards of the large int-
                     estine. Marketed seasonally in the U.S.

Ears        0.60     Generally exported to Latin America but also enj-
                     oyed in U.S.

Fat         25.0     Amount of backfat depends on the grade of hog.  
                     Lard provides a source of energy and an essential  
                     fatty acid (linoleic) for the human consumer; it  
                     is easily digested, since its melting point is  
                     near body temperature. Lard is useful as a cooking  
                     fat, a shortening, and a flavor ingredient in many  
                     foods. Unrendered fat is used in processed meat,  
                     soups, and snack products.

Feet (front)1.4 each Sold both in domestic and foreign markets.

Heart       0.6      Many are exported. They are normally split and wa-
                     shed. Some sold fresh to be cooked with moist heat.  
                     Most used in sausage manufacture as indicated on  

Intestines           (Also see chitterlings)
                     Sausage casings
                          Small intestine -20 yards
                          Large intestine -"Middle" 15-inch cap end (fr-
                                         ont end near small intestine)
                                         Bung afterend - one yard (front  
                                                         end of bung)
                                         Bung fatend - one yard (rear  
                                                       end of bung)

Kidneys     0.25 eachSold to Western Europe for human food to be sauteed  
                     and served with a sauce. Many used in U.S. for pet  

Liver       3.25     Small U.S. market for pates and braunschweiger.  
                     Excess goes to pet food. Some exported to Western  
                     Europe for human food.

Lungs       1.0      Some people of the world utilize lungs in processed  
                     meats, sausages, and stuffings. Most go to pet food  
                     in the U.S.

Maws        1.5      Used in U.S. and exported to Mexico for soup.

Mechanically         Yield of 21-27% from ham and picnic bones. Bones  
Seperated Pork       are coarse ground,then forced against a sieve to  
(MSP)                remove soft meat which flows through the holes.  
                     Use is limited and "mechanically separated pork"  
                     must be indicated by label.

Salivary    0.1      Used in Chorizo, a highly spiced, hot, dry Hispanic
glands                     sausage.

Spleen      0.4      Edible in the export market; mostly used for pet  
(melts)              food in the U.S.

Skin       10.0      Normally only skin off the back fat, fresh hams,  
(whole skin)         and bellies is saved for human food, i.e., gelatin  
                     manufacture and pork rinds (snack foods). Gelatin  
                     finds wide use in desserts; in the manufacture of  
                     ice cream; in the making of certain pharmaceutical  
                     preparations and capsules for medicine; in the  
                     coating of pills; in the making of mayonnaise dre-
                     ssings and emulsion flavors; and in the clarifying  
                     of wine, beer, and vinegar. Pork skin is also used  
                     to manufacture cosmetics.

Snouts      0.65     Used in processed meat products.

Sweetbreads 0.25     Demand for human food is diminished, so most go  
(pancreas)           into pet food.

Tail        0.25     Sold domestically for an ethnic market or exported  
                     to Latin America.

Testicles   0.40 eachFrom young animals preferred for human food, usua-
                     lly thinly sliced, breaded and deep-fat fried. Most  
                     go to pet food and to inedible products.

Tongue      0.75     Most exported to Western Europe and Japan. Some dem-
                     and as fresh product and for canned and processed  
                     meat products.

Uterus      0.75     If saved for human food, exported to Far East to be  
                     used in Orienal dishes.

Weasand     0.13     Sausage manufacture.

Table 2. Proximate protein, fat and calorie content of 100  grams
of selected cooked pork variety meats.
| Variety Meat               Protein        Fat        Calories |
|                            (grams)      (grams)               |
| Brain                        12.2         9.5          138    |
| Heart                        23.6         5.05         148    |
| Kidney                       25.4         4.7          151    |
| Liver                        26.0         4.4          165    |
| Lung                         16.6         3.1           99    |
| Pancreas (sweetbreads)       28.5        10.8          219    |
| Spleen                       28.2         3.2          271    |
| Tongue                       24.1        18.6          271    |

From Agriculture Handbook No. 8-10, Composition of  Foods,  Pork,

     Because variety meats are  economical  sources  of  valuable
nutrients,  more  extensive  use  of  meat animal by-products for
human food has been proposed as one method to reduce world nutri-
tion  problems.  In  addition  to  enhancing human nutrition, new
developments in meat by-product utilization  would  increase  the
overall  efficiency  of  livestock  production. Variety meats are
relatively high in protein; the exception is brain. Liver is  the
most  nutritious of all meat items. The nutrient density of liver
exceeds that of muscle meats, which are high. An excellent source
of  readily  digested  heme iron, liver also provides B vitamins,
particularly B12, as well as vitamin A to consumers who enjoy its
unique  flavor.  (Heme is the O2 carrying component of hemoglobin
and myoglobin and is a source of iron more  readily  absorbed  by
the human digestive system than most dietary iron forms.)

Pharmaceutical By-Products

     The medical arts have used animal products  in  the  healing
process  for  centuries.  In fact, some animal products have held
``magical'' healing powers for certain societies throughout  his-
tory. Similar conditions exist today with minute portions of cer-
tain animal extractives which are used each day and can literally
be the difference between life and death for many humans. The pig
is often used as a model for human research because of the  simi-
larity  between  the  two species of several vital systems. Thus,
most of the healing effects described below  apply  to  pigs  and

     Internally secreting, ductless endocrine  glands  are  scat-
tered  through  various  parts  of the animal body. The substance
secreted by each exercises some specific control  over  the  con-
duct, character, and development of the body. Their functions are
so interrelated that under-  or  over-secretion  of  any  one  of
several of the glands will cause abnormalities. Hormones are some
of the "magical" products which are derived from  animal  tissues
saved by the meat industry and which are extracted, purified, and
prepared for consumers by the  pharmaceutical  industry.  Enzymes
and  other  types  of  chemicals  are  also  derived  from animal
slaughter by-products.


     The adrenals are also called the suprarenal glands  and  are
two  in  number.  They are long and narrow and are located on the
medial border of the kidney. They are reddish-brown in color  and
somewhat bean-shaped. The cortex (outer portion) produces steroid
secretions essential to life maintenance. The medulla (inner por-
tion)  of  the  gland  produces  epinephrine which constricts the
blood vessels and increases  heart  action.  Each  adrenal  gland
weighs approximately 1/2 ounce (14 grams).

     Until recently hog adrenal glands were an  important  source
of  many  different  hormones  which  physicians  used  to  treat
illnesses or chemical imbalances in the human body. Now, many  of
these compounds are made synthetically.


     The thyroid gland is dark and  triangular  shaped,  about  2
inches  across, may be located some distance from the larynx, has
no isthmus, and somewhat adjoins the esophagus. Its secretion  is
an  iodine-containing  compound  termed thyroxin. In the young, a
deficiency of thyroid tissue causes a condition known  as  ``cre-
tinism,''  resulting  in physical deformity and defective mental-
ity, or idiocy. In the adult, it  causes  a  condition  known  as
``myxedema,''  defined  as"severe  thyroid  deficiency" (hypothy-
roidism), characterized by dry skin and hair and loss of physical
and mental vigor.

     Forty fresh hog thyroids are needed to make a pound of  thy-
roxin (14 grams to 21 grams per gland).


     Parathyroids consist of four small  glands  the  size  of  a
grain  of  wheat.  They  are  located close to the thyroid gland.
Their secretions regulate the calcium content of the blood stream
and maintain the tone of the nervous system. The complete removal
of the parathyroids causes death within a few weeks. To secure  1
pound  of  parathyroid extract requires the slaughter of approxi-
mately 3,600 animals.

Nervous System

     Hog brains are a potential source of  cholesterol,  the  raw
material  from  which vitamin D3, the ``sunshine'' vitamin neces-
sary in building bones and teeth, is made. Cholesterol also comes
from the spinal cord.

     The hypothalamus, a small inner basal portion of the  brain,
produces  relatively  small  molecules  that cause the release of
various hormones from the pituitary gland.


     Located at the base of the brain and  well  protected  in  a
separate  bone cavity, the pituitary gland is about the size of a
pea and is grayish yellow in color. It is made up of an  anterior
and  a posterior lobe which have distinct functions. The anterior
lobe is known to produce (1) the growth-promoting  hormone  (GH),
(2)  the  thyroid-stimulating  hormone (TSH), (3) the luteinizing
hormone (LH), (4) prolactin, (5) the follicle-stimulating hormone
(FSH), and (6) the adrenal-cortex-stimulating hormone (ACTH). The
posterior lobe excretes hormones that (1) control blood  pressure
and  pulse rate, (2) regulate the contractile organs of the body,
and (3) govern energy metabolism. Pituitary glands in  hogs  pro-
duce  a great number of hormones used to control human growth and
metabolism problems and to regulate activity of the body's  other
endocrine glands.


     The pineal gland is about one third the size of  the  pitui-
tary,  reddish in color, and located in a brain cavity behind and
just  above  the  pituitary.  Its   secretion   regulates   early
growth-hastening  or  retarding  puberty  and maturity. The hog's
pineal gland secretes the hormone melatonin,  which  is  used  in
treatment  of  personality  and mental disorders. It also affects
the color of the skin and the formation of freckles.


     Linings of the hog's stomach contain  proteins  and  enzymes
used in many commercially produced digestive aids and antacids.


     Heparin is classified as one of the "essential" pharmaceuti-
cals  and  is  obtained  almost exclusively from the inner lining
(mucosa) of the hog's small intestine and from the lungs. It is a
natural  anticoagulant  used  to  thin  the  blood  and dissolve,
prevent, or retard clotting  during  surgery,  especially  during
organ  transplants.  Heparin is also used as a gangrene preventa-
tive in cases of frostbite and as a burn treatment.

     Enterogastrone,  a  hormone  taken  from  the  hog  duodenum
(beginning  of  the small intestine), is used to regulate gastric
secretions in the stomach. It  is  also  used  experimentally  to
speed  the  emptying  time of the stomach. Secretin hormone, also
from the duodenum, stimulates pancreas  glands  to  produce  pan-
creatic  juices.  It is injected in humans to test for disease of
the pancreas.

Liver and Spleen

     Bile is synthesized in the cells of  the  liver  and  passes
through  the  hepatic and cystic ducts to the gall bladder, where
it is stored. Cholic acid has been purified from bile. It  is  an
intermediate  in the formation of chenodeoxycholic acid and urso-
deoxycholic acid which are also derived from bile to be  used  in
the  treatment or prevention of gallstones. Catalase is an enzyme
from the liver that is used in dairy  processing,  mainly  cheese
making.  Splenic  fluid  affects capillary permeability and blood
clotting time and speeds up recovery from inflammatory conditions
(redness and swelling).

Testes and Ovaries

     Hyaluronidase, an enzyme that attacks the complex  glycopro-
tein,  hyaluronic acid, found in joints and other connective tis-
sues, is derived from testes. Hyaluronidase is used as a  spread-
ing  factor  to  aid drug dispersion in connective and other tis-
sues. Hog ovaries are a source of progesterone and estrogens used
to treat various reproduction problems in humans. Sow ovaries are
the major source of relaxin, a hormone often used  during  child-
birth.  It requires the slaughter of 145 female hogs to produce 1
pound of fresh ovaries  from  which  corpus  luteum  and  ovarian
extracts are prepared.


     Lungs may be used as a source  of  heparin,  but  intestinal
mucosal heparin extractions are more easily purified. Lung tissue
is a source of a pancreatitis treatment product called aprotinin.


     Hog heart valves from young pigs to full-sized  market  hogs
are  specially  preserved and treated and surgically implanted in
humans to replace heart valves that have been weakened or injured
by rheumatic fever or through birth defects.


     The pancreas is commonly known as the pork  sweetbread,  but
it  should  not  be confused with the commercial veal sweetbreads
(thymus gland). The  pancreas  has  both  internal  and  external
secretions, the latter passing into the small intestine to effect
the digestion of starch, protein, and fat. The internal secretion
(insulin)  regulates sugar metabolism. Failure of the pancreas to
regulate sugar metabolism results in the affliction known as dia-
betes mellitus.

     Diabetes was a killer disease before it was discovered  that
animal  insulin  could be used in humans. Insulin, first isolated
by Drs. Banting and Best, is secured from specialized  groups  of
cells  in the pancreas known as the islets of Langerhans. Insulin
is used extensively in treating diabetes.

     The pancreas glands from approximately 60,000 hogs produce 1
pound of pure insulin, enough to treat 750 to 1,000 diabetics for
one year. A year's production of 85 million market hogs could  be
the  source of 1,400 pounds of insulin. The chemical structure of
hog insulin most nearly resembles that of humans. This is  signi-
ficant  because approximately 5% of all diabetics are allergic to
insulin from other animals and can  tolerate  only  insulin  from

     A product referred  to  as  humulin  is  in  production  and
replacing animal sources of insulin. Although priced higher, dia-
betics  are  increasingly  using  humulin.  All  newly  diagnosed
patients are put on the new product and many animal insulin users
are being converted. This new product is a result of  biotechnol-
ogy  and is replacing porcine insulin as biotechnological methods
of synthesis become more efficient and cheaper.

     Glucagon is a pancreatic hormone given to  raise  the  blood
sugar  level and to treat insulin overdoses in diabetics, or when
a low blood sugar episode is caused by alcoholism. It has a  spe-
cialized use in the treatment of some psychiatric disorders. Kal-
likrein is a proteolytic enzyme from the pancreas which  is  also
called  kininogenase. It catalyzes a hydrolysis that forms kalli-
din. Kallidin dilates vascular  smooth  muscle  tissue  and  thus
reduces blood pressure. Chymotrypsin is an enzyme used to cleanse
wounds and to remove dead  tissue  where  ulcers  and  infections

     LPH (lipotropic hormone) is used as a digestive aid  and  is
important  in the digestion and absorption of fats and oils. Pan-
creatin is a mixture of pancreatic enzymes used to  treat  faulty
digestion  in  humans. Because of its high-fat digestive capabil-
ity, pancreatin is also used in the treatment of cystic fibrosis,
a disease afflicting approximately 4 million people in this coun-

     Trypsin is a digestive aid that helps  break  down  food  by
aiding  in  the  hydrolysis  of  protein in the upper part of the
small  intestine.  Trypsin  and  the  enzyme   chymotrypsin   are
prescribed  to remove dead and diseased tissue from wounds and to
speed healing after surgery or injury. Other extracts  made  from
the pancreas, such as pancreatin, are used as a remedy for intes-
tinal disorders.


     Gelatin from hog skin collagen is used for coating pills and
making  capsules.  Gelatin  is taken orally to improve fingernail
strength. See later discussion of pork skins as burn bandages.  A
porcine collagen product has been developed to stimulate clotting
during surgery. The product is applied directly on the surface of
the bleeding tissue.


     Blood albumin from meat animals is used in  human  blood  Rh
factor  typing.  Blood  fibrin  extract from hog blood is used to
make  amino  acids  that  are  part  of  parenteral  (infused  as
intravenous)  solutions  for nourishing certain types of surgical
patients. Fetal pig plasma is important  in  the  manufacture  of
vaccines  and tissue culture media. Fetal blood contains no anti-
bodies and is unlikely to stimulate immune reactions.

     Thrombin, a blood protein, helps  create  significant  blood
coagulation.  It is valuable in the treatment of wounds, particu-
larly in cases in which the injury is in an inaccessible part  of
the body, such as the brain, bones, or gastrointestinal tract (as
in the case of peptic ulcers). Thrombin  is  also  used  in  skin
grafting  to  help  keep  the graft in place and to "cement" gaps
where tissues have been surgically removed.

     Plasmin, a hog blood enzyme which has the unique ability  to
digest  fibrin in blood clots, is used to treat patients who have
suffered heart attacks. This proteolytic enzyme is combined  with
deoxyribonuclease from the pancreas to aid in the removal of dead
tissue that results from certain  vaginal  infections.  It  is  a
valuable cleansing agent for infected wounds or clotted blood and
can speed up the healing of skin damaged by ulcers or burns.  Hog
blood is also used in cancer research, microbiological media, and
cell cultures.

Inedibile Pork By-Products


     Meat slaughter and processing  plants  that  have  rendering
facilities  must have two separate rendering units. The two units
must be separated physically to prevent any intertransfer of  raw
material,  product,  or contamination from the inedible-rendering
area to the edible-rendering area. In pork operations,  all  soft
tissue,  some bones, sweepings, scrapings, and skimmings that are
not classified as edible or do not have other uses are cooked and
processed  into  inedible fat and meal by rendering. Dead hogs or
condemned pork  products  are  processed  by  inedible  rendering

     Rendered pork fat is known as grease. A major  domestic  use
of grease is animal feeds. These fats are usually stabilized with
an approved antioxidant to prevent  rancidity  development  which
would make the feed unpalatable. Fat is the richest food nutrient
in terms of energy and as such has been used successfully in cat-
tle,  poultry,  swine,  and  pet feeds. In addition to the energy
value, fats reduce the  dust,  improve  the  color  and  texture,
enhance  the  palatability,  increase  pelleting  efficiency, and
reduce machinery wear in the production of animal feeds.

     During 1987, the pet food industry produced approximately  9
billion pounds of dog and cat food at a 1987 retail value of $5.7
billion. Comparable figures were $350 million in  1958  and  $1.6
billion in the mid-1970s. Animal fats are used as energy sources,
and meat meal is used extensively in some  products  for  protein
and  mineral sources as well as for palatability enhancement. The
pet and animal food  industry  utilizes  some  fresh  by-products
(uncooked)  for  canned and fresh frozen pet and specialty animal
foods (zoo foods, mink food, racing and guard dog food,  and  fox

Fatty Acids

     Fatty acids are obtained from animal fats through a  process
referred  to as splitting and are used in ever increasing quanti-
ties in the manufacture of scores of products. The list  of  uses
for fatty acids and other derivatives of natural pork fats by the
chemical industry is extensive:  biocides-substances  destructive
to  many  different  organisms,  cellulose processing, cosmetics,
dyestuffs, explosives, fabric conditioners, foodstuffs,  lacquers
leather  and paper goods, linoleum, lubricants, metal soaps, min-
ing, mineral oil additives, plastics, road making rubbers, soaps,
synthetic  resins,  tobacco, textiles, varnishes, and washing and
cleaning agents.


     Lard oil, made from ``A'' white grease, is used for making a
high-grade  lubricant  which  is used on delicate running machine
parts. The oil from "B" white grease is sometimes  called  "extra
neat's-foot oil" and is used in giving viscosity to mineral oils.
The oils made from the brown grease are used in compounding  cut-
ting   oils,   heavy  lubricating  oils,  special  leather  oils,
illuminating oils, and are combined with paraffin in candle  mak-


     Lard oil is also used for the manufacture of soap. Prior  to
the  1960s,  the  greatest utilization of grease had been in soap
making.  During  the  mid-twentieth  century,   soap   production
declined  significantly,  due  primarily  to the increased use of
phosphate-based detergent powders and liquids.  Domestic  use  of
animal  fats  in soap has also been diluted by use of plant lipid
sources. This development of detergents and other cleaning agents
and  replacement  by  vegetable fats posed serious threats to the
market for the major products  of  the  rendering  industry.  New
markets  were  researched  and developed in the feed industry, in
the export market, and in application of fatty  acids  to  indus-
trial  uses.  The loss of a portion of the soap market stimulated
the renderers to expand markets and diversify the products of the

     Modern soap making occurs in continuous  processing  systems
which  utilize  fatty  acids  stripped from raw fats. Soap making
originated and remained a batch process involving more  time  and
less technology until the middle of this century.

     Soap is biodegradable and therefore has  an  advantage  over
the  phosphate-based  detergents that replaced soap for many uses
some years ago. Phosphates tend to accumulate in the water supply
and  are responsible for the stimulation of algae growth and oxy-
gen depletion in lakes and streams. Fat-based  cleaning  products
with  detergent-like  traits,  effective  in hard and cold water,
have been developed and are in use in various parts of the world.
Environmental  concerns  and  fat utilization research have rein-
stated fat-based materials in the cleansing market.

Meat Meals

     The dry, defatted, high-protein material which results  from
rendering  varies,  depending  on  the raw materials used and the
processing technique employed. Protein products of rendering  may
be utilized in a number of ways but are marketed most extensively
as animal feeds. It is necessary that the  nutrient  content  and
availability  of feed ingredients be standardized, because animal
nutritionists  have  detailed  knowledge  of  specific   nutrient
requirements  and  are  using  computers  to  balance  diets  for
specific amino acids and micronutrients. Animal  protein  sources
used  in  livestock  diets have not been well-standardized in the
past. However, the U.S. rendering industry is installing  render-
ing  systems  that  result  in  less heat damage to nutrients and
improved quality control of raw materials and handling.  This  is
an  effort  to standardize rendered protein products. In addition
to reducing variation in nutrient content and  availability,  the
improved  methods  reduce  potential  microbial  contamination of
valuable feed ingredients.

     Most nonfat products  (of  rendering)  may  be  utilized  as
organic  fertilizers.  Some  adhesives  utilize  animal proteins,
especially blood meal or dried blood,  as  base  materials.  Bone
meal  is marketed to the manufacturers of china, instrument keys,
steel alloys, glass, water-filtering agents, and enamels.

     The major nonfat products of rendering are  described  below
as  feedstuffs,  since that is the principle use of the materials
listed. The International Feed Number (IFN), which is an identif-
ication  system  for feed ingredients, is indicated for each pro-

     Tankage, Digester Tankage,  and  Wet-rendered  Tankage:  IFN

     The meat animal soft-tissue by-products and dead animal tis-
sues   have  been  rendered  using  direct  steam-pressure  (wet-
rendering) systems. Dried blood is often added. The crude protein
level  is  high  (55% to 60%), but availability of and amounts of
certain essential amino acids are low. Tankage is a  good  source
of calcium and phosphorus.

     Tankage, with Bone: IFN 5-00-387

     The product has increased calcium and phosphorus levels (4.4
%  or  more), with a corresponding decreased protein level. It is
similar to tankage but with a greater amount of bone.

     Meat Scrap(s), and Meat Meal: IFN 5-00-385

     The raw materials are similar to tankage but are rendered in
steam-jacketed  tanks  (dry rendering). The lower processing tem-
peratures result in improved protein quality. Dried blood is  not
added to meat meal, as is often true for tankage. When phosphorus
exceeds 4.4%, the product must be identified  as  meat  and  bone

     Meat and Bone Scrap or Meal: IFN 5-00-388

     The addition of bone to meat  scrap  increases  calcium  and
phosphorus content and reduces protein; therefore, its value as a
feed ingredient is reduced in some cases.

     Blood Meal: IFN  5-00-381  spray,  5-00-380  meal,  5-26-006

     Dried blood is high in protein (80%), especially  the  amino
acid  lysine but unpalatable as a feed ingredient and has reduced
digestibility. Flash dried (atomized  into  hot  vacuum  chamber)
blood  is a better quality feed source. Plasma is the watery part
of blood left when red cells are removed.  When  spray  dried,  a
process  that  does  not  destroy  the  fluid's protein and amino
acids, it may be used as a  protein  supplement  in  pig  starter
diets.  Blood  products  are  used  as adhesive bases and bonding

     Bone Meal, Steamed Bone Meal, and  Special  Bone  Meal:  IFN

     Bones are ground and rendered to remove the  fat  and  mois-
ture, and the largely mineral remainder is reground. The composi-
tion may vary due to differences in raw materials  or  processing
techniques and contains 7% to 15% protein.


     Most U.S. pork processors have used or are presently using a
scalding  and  dehairing technique which leaves the skin attached
to pork carcasses until they  are  processed  into  wholesale  or
retail cuts. With such a system, the only fresh skin available of
any consequence is that resulting from the fatback and the  hams.
This  skin  is  largely used in gelatin production. However, more
packers are removing the whole skin rather than dehairing,  which
results in pork skin usable for leather.

     Pigskin is used as leather for  gloves,  wallets,  handbags,
brief  cases, toiletry cases, tobacco pouches, book bindings, and
leggings. The  pigskin  leather  is  tough  and  produces  scuff-
resistant  footwear.  The hog bristle (hair) is unique in that it
grows through the skin from the follicle in the subcutaneous  fat
layer.  The holes, or pores, through which the hairs pass, result
in a naturally "air-conditioned" type of leather.

     Scalded skins can be pulled using  skinning  equipment,  but
the  leather  becomes  10%  thinner and has less tensile strength
than does the leather  from  unscalded  skins.  The  heat  damage
incurred  during  scalding makes many skins unsuitable for use as
leather. Scalding is more labor efficient when  done  during  the
slaughter phase; additional labor is required to remove the skins
at later stages of processing.

     Specially selected and treated hog skins, because  of  their
similarity  to  human  skin,  are used in the treatment of humans
suffering from massive burns and injuries that have removed large
areas  of skin. It is also used in the healing of persistent skin
ulcers. Hog skins are cut  into  strips  or  patches,  shaved  to
remove  the hair, split to 0.008 inches to 0.020 inches in thick-
ness, and then cleansed, sanitized, and packaged. The  skins  are
applied  directly  to the injured areas to decrease pain, inhibit
infection, and prevent loss of body fluids.

Glue and Gelatin Stocks

     The three main types of glue are hide glue, bone  glue,  and
blood  albumin  glue.  The  latter is water resistant and is used
widely in the manufacture of plywood.

     The oldest and widest use for glue is in the  furniture  and
veneer  industry.  Glue  has so many varied uses that it has been
said that glue holds the world together. It  is  used  in  sizing
paper;  in  the  manufacture of wool, silk, and other fabrics; in
sizing straw hats; in sizing walls that are  to  be  painted;  in
sizing barrels or casks that are to contain liquids; on the heads
of matches to make an air-tight cap over the phosphorus;  in  the
manufacture  of  sand and emery paper to hold the abrasive on the
paper; in the manufacture of dolls, toys, and ornaments;  in  the
making  of  picture  frames,  mirror  frames,  rosettes, billiard
balls, composition cork, imitation hard rubber,  printing  rolls,
mother-of-pearl,  gummed tape, paper boxes, calcimine, automobile
bodies, caskets, leather goods, and bookbinding; and  many  other

     The two types of gelatin according to their source are  hide
gelatin  and  bone gelatin. Both types of gelatin are used in the
making of ``facial'' court plaster, in photography,  in  electro-
plating,  as  a  bacteria  culture  medium, and for various other


     Whole blood contains around 21% protein.  If  the  blood  is
allowed to coagulate, the gelled portion contains fibrin and cel-
lular proteins, whereas the blood albumin remains  in  the  fluid
serum.  The  fibrin  portion is sold as dried blood in tankage or
fertilizer. The serum is clarified and dried and  sold  as  blood
albumin.  Blood  albumin  is used in certain malt extracts and in
fixing pigment colors in cloth and in finishing leather, clarify-
ing  liquors,  and  manufacturing glue. Blood is also used in the
manufacture of buttons and imitation tortoise shell articles.


     Hog bristles for making brushes were formerly imported  from
China  but  are  now  produced in the United States in increasing
amounts. It requires  considerable  hand  labor  to  collect  the
proper length bristles. It is found over the shoulder and back of
the hog. The fine hair of most of our domestic hogs is not  suit-
able  for brush making; it is processed and curled for upholster-
ing purposes.

National Live Stock and Meat Board, 444  North  Michigan  Avenue,
Chicago, IL, 60611.
National Pork Producers Council, P. O. Box 10383, Des Moines, IA,
Pearson, A. M., and T. R. Dutson. 1989. Edible Meat  By-Products.
In:  Advances in Meat Research. Vol. 5. Elsevier Science Publish-
ers, Ltd., New York, NY.
Romans, J. R., K. W. Jones, W. J. Costello, C. W. Carlson and  P.
T.  Ziegler.  1985.  The  Meat We Eat. (12th Ed.). The Interstate
Printers and Publishers, Danville, IL.
USDA. 1990. Livestock and Poultry Situation and  Outlook  Report.
LPS-43, Economic Research Service,

NEW 12/90 (7M)


Cooperative Extension Work in  Agriculture  and  Home  Economics,
State  of Indiana, Purdue University and U.S. Department of Agri-
culture Cooperating. H.A. Wadsworth,  Director,  West  Lafayette,
IN. Issued in furtherance of the Acts of May 8 and June 30, 1914.
It is the policy of the Cooperative Extension Service  of  Purdue
University  that  all  persons  shall  have equal opportunity and
             access to our programs and facilities.