Animal protein meals

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Although the production of animal protein for human consumption has been under continual pressure and marred by much controversy, the world-wide and domestic consumption of animal protein continues to grow. The Food and Agriculture Organisation of the United Nations (FAO) (2002) predicts that the level of world consumption of animal protein for the year 2000 will increase by 60% by 2020; much of the meat protein will be from poultry and the FAO is also predicting a 30% increase in egg production. With increased animal protein production there will be increased demand for feed and, in particular, a demand for ingredients high in protein and energy.

The animal industry evolved as a means of adding value (i.e. higher nutrient level and availability,flavour, variety, etc.) to ingredients that were of marginal food value for humans. These ingredients include grains that are of poor quality or damaged by harvest or storage conditions; and, as a meansof recycling, by-products of brewing, vegetable oil, meat, milk and egg production. Approximately 50% of the live market weight of ruminants and 30% of poultry is by-product. These by-products are rendered, ground and available as a feed source. This fact sheet will discuss the issues and opportunities associated with recycling animal protein meals through poultry in the production of meat, eggs and bioproducts.

Animal protein meals

Animal protein meals are usually defined by inputs, those specifically used in poultry diets include: meat (no bone) or meat and bone meal (from ruminants and/or swine); blood meal; poultry by-product meal; feather meal; and fish meal. There are specific limitations now assigned to these products with regards to inputs used and guarantees with respect to minimum nutrient levels. For example meat and bone meal may be specifically from ruminants and must be free of hair, wool and hide trimmings, except where it is naturally adhering to heads and hoofs. The products are all rendered which is a biosecure process that evaporates water, extracts fat and yields a finished ground product high in protein (which has no resemblance to the raw product) and minerals. The products are marketed with guarantees as to minimum protein, phosphorus and calcium levels.

The issues

Food safety is the most important concern people have about the recycling of animal protein meals back through animals as feed ingredients, and this is based on possible (i.e. not medically proven) links between bovine spongiform encephalopathy (BSE – mad cow disease) and a new variant Creutzfeldt-Jakob disease in humans. The proteins (prions) associated with BSE are not destroyed by traditional methods of rendering and are capable of causing the disease when contaminated meat and bone meals are injected cerebrally into ruminants (but not when provided in feed under laboratory conditions). Researchers have been unable to demonstrate the transfer of prions to poultry and no symptoms of disease have been observed in birds up to five years after direct challenges.

As a consequence of the public’s concerns about BSE, Australia has banned the feeding of ruminant by-product back to ruminants; however, this product is available to the poultry industry. The Australian cattle and sheep industry has adopted this practice even though Australia is free of BSE and all other transmissible spongiform encephalopathy such as Scrapie and Chronic Wasting Disease (Aird and Spragg, 2003).

Further to BSE are concerns that animal protein meals are responsible for food borne pathogen contamination, such as Salmonella. Typically these bacteria are destroyed by rendering and possible recontamination is often negated by pelleting of manufactured feeds. In most cases, if poultry acquire Salmonella it is likely to be from an environmental source other than feed. It is possible for animal protein meals to be contaminated with high levels of heavy metals, dioxins and PCBs (pesticides); however, meals are monitored and regulated to minimise this.

Feeding animal protein meals

With respect to feeding the animal protein meals, the most crucial dilemma facing a nutritionist is the variability in available nutrients (those that can be absorbed and retained by the bird) and limits to incorporation to maintain a diet balanced for all nutrients, particularly calcium and phosphorus. The table below indicates the averages of samples used in developing nutrient levels published by the National Research Council (NRC, 1994) for meat and bone, blood, feather and poultry meals.

Table 1: Nutrient levels in animal protein meals

Nutrient	Meat & Bone	Blood	Feather	Poultry
Metabolisable Energy (MJ/kg)	11.2	15.2	13.7	13.1
Crude Protein %	50.4	88.9	81.0	60.0
Fat %	10.0	1.0	7.0	13.0
Calcium %	10.3	0.4	0.3	3.0
Phosphorus %	5.1	0.3	0.5	1.7
Lysine %	2.6	7.1	2.3	3.1
Methionine %	0.7	0.6	0.6	1.0
Cystine %	0.7	0.5	4.3	1.0

Source: adapted from Hamilton (2002)

Animal protein meals provide a good source of essential amino acids (e.g. lysine and methionine), but they are also good sources of energy and minerals (particularly calcium and available phosphorus). There can however be significantvariation in availability (absorption and retention) of amino acids due to the day to day variation in inputs as well as processing conditions (temperature, moisture, pressure and time). Ravindran et al. (2005) concluded that variation in meat meal quality (amino acid availability) within processing plants was greater than variation between plants. It is important for users to establish strict criteria as to quality of product and work with their suppliers to ensure these criteria are met. Quality should include measurements that indicate moisture; nutrient availability (particularly essential amino acids); levels of minerals (for example, calcium can vary from 8–12%; phosphorus from 4–6%); and stability of fat (all meals should be stabilised with an antioxidant).

The most accurate way of measuring the “feed value” of an ingredient is to use an animal assay or bioassay. However, these assays are extremely time consuming and expensive. One of the most promising predictors of nutrient level and availability is near-infrared reflectance spectroscopy. This technology is rapidly being adopted by feed manufacturers and enables rapid screening of incoming products for a wide variety of measurements (moisture, protein, amino acid availability, fat, etc.). In most cases the samples can be prepared, scanned and results assessed in less than a few minutes. However, calibrations are still being developed for meals and further research to classify the cause of variation in feed value is required. Animal protein meals have a long history in poultry nutrition. Utilisation of this valuable feed ingredient is important in minimising loss (nutrient and economic value) in our production of safe, high quality poultry meat, eggs and bioproducts.