TECHNICAL ARTICLES Broilers/Layers/Breeders

Animal by-products in poultry diets


Animal by-products was first introduced to the poultry industry in the 1880’s in New England, where the residue from the waste water was air dried on platforms outside slaughterhouses (Denton et al., 2005). It has been realised for many years that the performance of chickens on animal protein based diets are superior to their performance on vegetable protein based diets. Scottet al. (1969) reported that this was due to the calcium and phosphorous supplied by the bone in animal by-products, the abundance of B-complex vitamins, especially Vitamin B12 and higher concentrations of the amino acids, methionine and lysine, in animal proteins compared to that of plant proteins. Denton et al. (2005) also suggested that the exclusion of animal proteins in poultry diets may increase aggressive behaviour, such as feather pecking, due to a deficiency in various nutrients.

Table 1. Total estimated annual costs of methods for mortality disposal in the United States compared to rendering (Sparks Co. Inc., 2002).

1 Assuming all dead stock was rendered; 2 Meat- and bone meal; na: Not applicable

The poultry industry is the major consumer of animal protein, using over 36 % of all animal by-products in the United States (FDA-ANPR, 1996). It has been calculated that the exclusion of animal by-products could result in a 5 to 10 % increase in the cost of producing animal feeds (Leeson, 2002), as this would imply higher inclusion of more expensive inorganic calcium and phosphorous, synthetic amino acids and other alternative sources of highly digestible protein. In South Africa it has been estimated that the exclusion of poultry by-product meal and blood meal from broiler diets could result in an increase of R70 to R90 per ton of broiler feed (3 to 5 %).

Alternative means of disposing of livestock mortalities such as burying, incinerating or composting has been found to be financially unfeasible in the United States, due to high initial investment costs (Table 1). From this study, burial may be an alternative, but rendered meat- and bone meal sold to the feed industry would still be US$ 16 428 000 cheaper per year (Table 1). Alternatives to rendering may also result in pollution of ground water (burial), excessive smoke (incinerating) and unpleasant odours (incinerating and composting) ( Sparks Co. Inc., 2002) . These disposal methods may also lead to the spread of pathogens (Dentonet al., 2005) endangering human and animal lives. The rendering industry therefore plays an important role in disposing of the unwanted waste generated from animal production and provides value added products to the animal feed industry.

Bovine Spongiform Encephalopathy andSalmonellarisk

The outbreak of Bovine Spongiform Encephalopathy (BSE) in Europe in 1986 and its possible relation to the new variant Creutzfeldt-Jakob disease in humans, led to consumer concerns regarding BSE-related human illnesses. Epidemiological studies indicated that the feeding of meat- and bone meal to ruminants was responsible for this outbreak (Wilesmithet al., 1988). The agent responsible for this disease has not yet been completely identified. In theory such an agent can for example be a virus with unusual characteristics, a prion protein (an exclusively host-coded protein), or a virino (a small non-coding regulatory nucleic acid) (Traylor, 2005).

In the United Kingdom there were 60 reported cases of BSE in 1986, which escalated to 36 682 reported cases in 1992 (Pattison, 1998) and 178 000 reported cases in 2005 (Traylor, 2005), which occurred despite the ban on feeding of ruminant derived by-products to ruminants from 1988. This might have been due to the long incubation period (4 to 5 years) of BSE ( Stekelet al., 1996) further complicating accurate diagnostics.

Consequently, the European Union’s scientific advisory body, the European Food Safety Authority (EFSA), concluded that animal by-products derived from animals that are not fit for human consumption should not enter the feed chain and that such materials should be properly handled and disposed after adequate processing, to prevent the possible spread of pathogens. Consequently the European Parliament from May 2003 only permitted the use of animal by-products in animal feeds if declared Category 3 material (fit for human consumption) (Regulation EC No. 1774/2002) and if permitted by the transmissible spongiform encephalopathy (TSE) Regulation No 999/2001. However, following issues raised by member states, a new Regulation (Regulation EC No 79/2005) was adopted, permitting the use of Category 3 milk-based products for direct feeding to farm animals.

Although BSE has never been diagnosed in South Africa or any other country in Africa, legislation exists that controls the use of animal by-products. Under Act 36 of 1947 the use of any ruminant or porcine protein and/or by-products (except milk and milk by-products) is prohibited except where feed is manufactured for cats and dogs. Act 36 was revised in November 2006 which again permits the use of ruminant derived blood and tallow in animal feeds. It is likely, however, that government will revert back to the original Act 36 as endorsed in Notice 1360 of 2006 (published in the Government Gazette on 22 September 2006), reintroducing the ban on the feeding blood meal (and tallow). This is due to concerns of contamination of blood with brain tissue as a result of captive bolt stunning prior to slaughter (personal communication). Government plans to increase the supply of blood to the pet food industry to avoid disposal issues encountered with the previous ban. Whether this alternative will be feasible, remains debatable as the pet food industry is currently only using 2 to

3 % of the approximately 10 000 tons of blood produced annually.

The species of which the animal by-products are produced may also differ in the risk of BSE-transmission (Dentonet al., 2005; Hamilton, 2002). By using DNA-technology such as ELISA methods, the identification of specie-specific by-products used to produce the animal meal may be possible in future when these methods become cost-effective. This may re-allow the use of non-ruminant by-products in animal feeds by the European Union, as these species have not been implicated in any BSE-cases ( Hamilton, 2002).

It is known that animal feed produced from raw materials of animal- and plant origin may be contaminated withSalmonellae, but the most serotypes associated with human disease (S. Enteritidis and S. Typhimurium) are rarely isolated from animal feed (Orris, G.D., 1997). Recently, Franco (2005) found that only 7.5 % of 197Salmonella-positive animal protein meals were associated with food born illness. Raw materials are, however, not the major contributor toSalmonellacontamination of feed products. Rodents, cats, insects and even the drinking water are greater potential reservoirs ofSalmonellathan feed itself ( Hamilton, 2002).

Meat- and bone meal

Meat- and bone meal is mainly derived from bones and associated tissues (tendons, ligaments and some skeletal muscle) as well as parts of the gastrointestinal tract, lungs and condemned livers (Ravindran and Blair, 1993).

Table 2. Chemical composition and amino acid concentration of soyabean meal some commonly available animal protein by-products.

1 3.5 to 7 % crude fiber; 2 Drum dried; 3 High fat; 4 Dig: Digestible amino acid content; 5 DC: Digestibility coefficient; a European Table of Energy Values for Poultry Feedstuffs, 1989; b Ravindranet al., 2005; c Wang and Parsons, 1998a; d Ravindranet al., 1999.

Meat- and bone meal can be manufactured by two processes namely “batch systems” and “continuous systems”. In the “dry batch rendering” system, the ground carcasses are heated to 100 °C in a cooker and dried at normal atmospheric pressure. The temperature of the residue is thereafter increased to 140 °C, resulting in cell rupture with the release of the fat content. In the “wet batch rendering” systems, the ground carcasses are subject to higher pressure and temperatures of 140 °C, by injecting steam into the cooker, whereafter the pressure is released, resulting in a decrease in temperature to approximately 100°C. Continuous systems work on the basis of heating (by essentially the same principle as in batch systems), separating the tallow and water from the meat- and bone meal and cooling of the raw material on a more automated basis. These processing conditions will to a large extent be determined by the physical quality of the raw material, especially the moisture and fat content. For example, a product high in fat and low in moisture would have to be cooked at lower temperatures to prevent the moisture being driven off too quickly and the meat- and bone meal therefore “frying” in the tallow. Depending on the specific continuous system being used, cooking temperatures range from 104 °C to 145 °C and cooking time at these temperatures between 15 and 65 minutes (The BSE Inquiry: The report). The European Union requires that all animal by-product meals should be processed at 133 °C and 207 kPa for at least 20 minutes to ensure that meat- and bone meal is a safe ingredient to use in animal feeds (Shirley and Parsons, 2000).

South Africa produces only 4 800 tons of meat- and bone meal annually from a possible

9 634 tons offal, all of which is used in pet foods. A further 25 000 tons of meat- and bone meal is also imported for the pet food industry (personal communication). Under Act 35 of 1984 meat- and bone meal from ruminant origin was banned (May 2001) from being used in all animal feeds, except for cats and dogs.

Meat- and bone meal is a good source of crude protein, calcium and phosphorous for poultry diets, but is inferior to other animal protein products such as blood meal and fish meal (Table 2). The phosphorous in meat- and bone meal is also highly available for poultry (Waldroup and Adams, 1994). Waldroupet al.(1965) reported that the biological availability of phosphorous from fish meal, poultry by-product meal and meat- and bone meal were 102, 101 and 102 % respectively, compared to that of mono- and dicalcium phosphate. Classification of this product depends on the concentration of crude protein and phosphorous, or then the ratio of bone to soft tissue, therefore, if the crude protein content is higher than 55% and the phosphorous content lower than 4.4% it may be classified as meat meal, or meat- and bone meal if the crude protein content lower than 55% and the phosphorous content higher than 4.4 % (Ravindran and Blair, 1993). The nutritional value and amino acid concentration of this by-product is also negatively correlated with the ash content (Karakaset al., 2001). Karakaset al. (2001) showed that the metabolisable energy (AME n) of meat- and bone meal varied between 10.51 to 13.04 MJ/kg DM, which correspond well with that of the European Table of Energy Values for Poultry Feedstuffs (1989), where AME n values of 10.35 and 13.50 MJ/kg DM has been estimated for normal meat- and bone meal and high fat meat- and bone meal, respectively. Karakaset al. (2001) showed that the ash content was negatively correlated with metabolisable energy (AME n) and amino acid concentration of meat- and bone meal. The ash content is therefore important in evaluating the quality of meat- and bone meal for broilers. Ravindranet al.(2002) also established that the ash content in meat- and bone meal was negatively related to the digestibility of all amino acids, except for aspartic acid, threonine, serine, tyrosine, histidine and cystine. They reported that the amino acid concentration, as well as the ileal digestibility of amino acids in meat- and bone meal can vary substantially. The most limiting amino acid in meat- and bone meal is tryptophan followed by methionine and cystine (Ravindran and Blair, 1993), although Ravindranet al. (2002) later found that cystine was the first limiting amino acid. Wang and Parsons (1998b) evaluated the true amino acid digestibility of 32 meat- and bone meal samples and illustrated that raw material source, processing temperature, cooking time and cooking system significantly (P<0.05) influenced the true amino acid digestibility (Table 3).

Using meat- and bone meal in broiler diets may significantly reduce feed costs. According to Bozkurtet al. (2004) the inclusion of meat- and bone meal at 2 %, 3.5 % and 5 % in grower and finisher diets reduced the cost by 2.2 %, 3.7 % and 4.5 %, respectively.

Table 3. The true amino acid digestibility of 32 meat and bone samples from beef, pork or both and processed by different methods, temperatures and times (Adapted from Wang and Parsons, 1998b).

SEM: Standard error of mean amino acid digestibility. Thr: threonine; Cys: cystine; Val: valine; Met: methionine; Ile: isoleucine; Leu: leucine; Tyr: tyrosine; Phe: phenylalanine; Lys: lysine; His: histidine; Arg: arginine

Blood meal

Blood meal can be defined as dried ground blood that is manufactured from the fresh blood originating from animal processing plants, with batch cooking the simplest method to produce this by-product. Continuous cookers have replaced batch cookers as they are more energy efficient. In this process the blood is introduced into a steam-injected tubular vessel in which the blood solids condense. The blood solids and serum are then separated by a centrifuge and the blood solids dried in a continuous gas-fired, direct-contact rotary ring dryer or steam tube. Spray-drying refers to a method where tiny droplets of blood are sprayed under high pressure into a sterile chamber at about 200 °C, resulting in instant drying of the particles to form blood granules. This quick drying of the blood droplets ensures sterilisation and minimizes nutrient loss.

South Africa produces 10 423 tons of blood meal annually, excluding poultry blood, of which 240 to 360 tons are used in the manufacturing of pet food and the remainder in the animal feed industry (personal communication). The government only recently (November 2006) amended Act 36 of 1947 to re-allow the use of blood meal in monogastric diets due to the fact that there was no alternative means for disposal of the blood meal being produced.

The energy value (AME n) of blood meal for poultry varies from 12.85 MJ/kg DM (spray dried) to 13.90 MJ/kg DM (drum dried) (European Table of Energy Values for Poultry Feedstuffs, 1989). It is also a rich source of crude protein, essential amino acids, especially lysine, methionine, leucine and valine (Table 2), which makes it an excellent animal protein for poultry diets, especially when fish meal is short in supply. The amino acid content of blood meal is also highly digestible (Table 2). Liuet al. (1989) evaluated the true amino digestibilities of blood meal in turkeys and found it to vary between 86 and 91 %, except for the digestibility of isoleucine and cystine which were lower at 73.8 and 78.6 %, respectively. In this regard Ravindranet al. (2005) found that the apparent ileal amino acid digestibility of blood meal for broilers was high (73 to 89 %) which compare favourably with that of fish meal and soya bean meal (Table 2). They also reported a low variation of amino acid digestibility between blood meal samples.

Hydrolysedfeather meal

Dried and ground feathers may have a crude protein content as much as 95 %, the majority of which is in the form of keratin and basically indigestible to poultry. For this reason various processing procedures have been developed to hydrolyze the cystine disulphide bonds in keratin.

Steam hydrolysis of the feathers is the most common method of processing through which the protein and amino acid digestibility are increased. These processing conditions have to be very specific as too high temperatures and/or pressure may destroy some of the heat sensitive amino acids such as lysine. Continuous processing of the feathers should be avoided as feathers tend to “gum” and therefore has to be agitated either constantly or intermittently (Morris and Balloun, 1973). Morris and Balloun (1973) found that feather meals processed at 50 pounds per square inch, for 60 minutes, with intermittent agitation resulted in the best biological quality for broilers. Moritz and Latshaw (2001) using various combinations of time (45 to 106 minutes) and pressure (207 to 724 kPa) at a constant temperature of 149 °C, showed that feather meal processed at the lowest pressure had the highest nutritional value and vice versa. The digestibility of cystine was, however, significantly decreased by more extreme processing conditions.

To avoid possible over processing, alternative methods to produce feather meal have been developed. The cystine disulphide bonds may also be enzymatically cleaved by bacterial proteases or chemically, with sodium hydroxide. Kim and Patterson (2000) found that such a enzymatically and chemically combined product was more effective in improving the AME n of feathers compared to only sodium hydroxide treatment. Sodium hydroxide is, however, a good reducing agent, which also increases feather solubility, pepsin digestibility andin vitroamino acid digestibility (Kim et al., 2002).

Feather meal has an AME n of 13.45 MJ/kg DM and is a good source of cystine and crude protein (Table 2) but is deficient in lysine and methionine as compared to major protein rich ingredients being used in poultry diets (Table 2). The overall amino acid digestibility of feather meal has also been found to be poor at approximately 61 % (Ravindranet al.,2005), with that of cystine being especially low at 35 % (Table 2). Hydrolysed feather meal should therefore be regarded as a supplement rather than a feed ingredient, except when it is processed together with poultry offal (Wilderet al., 1955; Lillieet al., 1956). Hydrolysed feather meal also contains the amino acid lanthionine which is not found in animal tissues and may be used as an indicator of the presence of feathers in other meat meals (Leeson and Summers, 2001).

Poultry by-product meal (PBPM)

PBPM is produced by dry-rendering techniques, similar to those used in the production of meat- and bone meal, from the waste generated during poultry meat processing and consists of mainly the viscera, heads and feet (Ravindran and Blair, 1993). In many instances PBPM also contains feathers or products such as hatchery waste which explains the variation in the nutrient content within and between products. When feathers are included, processing becomes more complicated as more intensive processing conditions are required to hydrolyze the keratin proteins. Over-processing will lead to a reduction of the protein quality of the PBPM. Papadopoulos (1985) reported that steam cooking of feathers at 146 °C and 320 kPa for 30 minutes produces a poultry meal of the highest digestibility and biological value. Due to this interaction in the processing conditions of feather meal and poultry offal meal, renderers abroad and recently also locally, prefer to manufacture a feather / blood meal and poultry meal separately. According to the South African regulation of sterilising plants (No R1086, 3 November 2006), PBPM has to be produced at a core temperature of more than 133 °C for at least 20 minutes at 300 kPa. With increased particle size these processing conditions are changed to 50 minutes at 120 °C. It is estimated that the local broiler industry produces 6 350 ton of poultry offal per week, of which approximately 1 700 ton of rendered meal can potentially be produced.

The possible contamination of PBPM withSalmonellaand/or other micro organi sms (Clostridia, Listeria, Camphylobacteretc.) is always a major concern. Although the above rendering processes sterilises the poultry by-product meal, recontamination may occur post processing as a result of poor handling and storage practices.

Table 4. Nutrient composition of 6 different poultry by-product meals (Adapted from Waldroup and Adams, 1994)

PBPM has an AME n of approximately 12.97 MJ/kg DM (Ravindran and Blair, 1993), which will vary considerably (10,92 to 13,55 MJ/kg) according to the poultry waste being used in the production of the PBPM (Waldroup and Adams, 1994, Table 4). The crude protein content of PBPM may vary between approximately 54 and 69 %, according to the inclusion rate of feathers and blood, while the fat and ash content may also be highly variable, between 11 and 17 % and 12 and 25 %, respectively. The higher inclusion of losses during transport to the rendering plant, will increase the fat content, while the inclusion of hatchery waste will increase the ash content of PBPM.

According to Ravindran and Blair (1993) and Main and Doghir (1981) the most limiting amino acids of PBPM is lysine and methionine, although Wang and Parsons (1998a) found it to be cystine and tryptophan (Table 2). However, if the quality and composition is well controlled, PBPM is a very good and cost effective protein source to replace fish meal and other animal by-products in broiler diets. Wang and Parsons (1998a) reported that the digestibility of amino acids in four pooled PBPM varied between 78 % and 89 % (Table 2), with cystine at a low digestibility of 46 %, which might have been as a result of improper processing conditions of the feather component of the PBPM.

Potter and Fuller (1966) examined the growth of broiler chicks (4 to 25 days) to high fat PBPM and fishmeal and reported that chicks fed the PBPM (5 %) had a significantly higher weight gain than those fed on fishmeal based diets. Recently, Isikaet al. (2006) reported that PBPM and hydrolyzed feather meal may have a synergistic effect in broiler diets. The retention of crude protein and fat was significantly higher in the starter diets with a 50:50 combination of PBPM and hydrolyzed feather meal, compared to using only a high fat PBPM.


The use of nutrient-rich animal proteins in the animal feed industry has a long history and allows for cost effective and flexible feed formulations. The potential variability in the quality of animal by-products is an ongoing challenge, which can be addressed by effective quality assurance systems. The availability of accurate and up to date amino acid and energy data on animal by-products, especially that of poultry offal and feather meals, are a restriction on the optimum usage of such materials.

Many food borne related illnesses (such as BSE) and concerns are largely as a result of misinformation and have not necessarily been scientifically proven. The use of ruminant- or mammalian derived protein, as well as poultry offal meals, can safely and economically be used in monogastric diets replacing fish meal and vegetable proteins such as soya oilcake and full fat soya.

Alternative methods for disposing of the large quantities of waste generated by food producers are environmentally hazardous, socially unacceptable and financially unfeasible. Renderers, especially poultry offal manufacturers, play an important role in the production of biological safe animal by-products and provide value added products to the feed industry.

For the continued usage of animal by-products in the feed industry, especially in monogastric diets, manufacturers should adhere to strict quality control systems to ensure that high quality products are produced that are safe for animal an inadvertently human consumption.

Contact Details :

For further information please contact the authors at 011 991 6000.


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Date published: 2007-01-03

Attie Venter