I Sci Food Agric 1988, 45, 223-230
Agriculture Group Symposium Recent Developments in Animal Feed Additives
The following are summaries of papers presented at a meeting of the Agriculture Group of the Society of Chemical Industry held on 16 February 1988 at the Society of Chemical Industry, 14-15 Belgrave Square, London S W l X 8 P S . The papers published have not been refereed and do not necessarily reflect the views of the Editorial Board of the Journal of the Science of Food and Agriculture.
Principles of Probiotic and Antibiotic Use in Animal Feeds
AFRC Institute of Food Research, Reading Laboratory, Shinfield. Reading RG2 9AT. UK
Probiotics are live bacterial feed supplements which protect against disease and stimulate the growth of farm animals, two functions traditionally performed by antibiotics. The probiotic concept is based on the knowledge that the indigenous intestinal microflora is capable of protecting the host animal against infection. Thus germ-free animals are often more susceptible to intestinal pathogens thar are conventional animals which have a naturally acquired complex intestinal microflora.
Modern methods of maintenance, feeding and therapy often upset the balance of the intestinal flora. The administration of a probiotic seeks to make good these deficiencies in the gut microflora and restore normal levels of resistance and growth.
Most of the probiotic preparations currently available contain lactobacilli, bifidobacteria and streptococci, all genera that occur naturally in the gastrointestinal tract. There is, therefore, no danger of harmful residues in the meat. Nor do they produce antibiotic-resistant populations of bacteria, making subsequent treatment difficult.
J Sci Food Agric (45) (1988)-0 1988 Society of Chemical Industry. Printed in Great Britain
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The ability to colonise the gut is of paramount importance to a good probiotic. Some of the factors which influence colonisation are known and these can be used to select suitable strains for use as probiotics.
At present not enough is known about the mode of action of probiotics to allow us to maximise the effect. When this sort of information becomes available, we will be able to develop more effective strains by augmenting the desirable features.
Technical Considerations for the Selection of Animal Feed Flavour and Flavour Enhancers
Clifford A Adams
Technical Department. Kemin Europa NV, lndustriezone Wolfstee. 241 0 Herentals. Belgium
Of all the feed additives currently on the market, flavours are probably the most difficult to select, to analyse and to utilise in animal feed manufacture. This is as a result of various factors listed below:
(1) Expected role of flavours. Feed manufacturers may require flavours to mask unpalatable feed ingredients, give uniformity to feed formulations, stimulate voluntary intake of feed, or give feed an attractive aroma.
( 2 ) Range of flaoours. Thereis-an enormous range of flavour products such as fruit- based flavours, enhancers, sweeteners and spices.
( 3 ) Animal species. Mammals in general are attracted to sweet-tasting substances such as sucrose or molasses and fruit flavours. Poultry do not respond strongly to sweet products but do have some sense of taste and will accept or reject various substances. Small animals often do not eat adequate quantities of commercial feed and may respond more avidly to flavoured feeds.
(4) Fluvour chemistry. Flavours are very complex mixtures of ingredients with different degrees of volatility and taste. Interaction of components with enhancers such as nucleotides, monosodium glutamate and thaumatin is important. Flavour ingredients are based on a large number of different esters, aldehydes, alcohols and natural oils.
( 5 ) Quality control. The chemical complexity of a flavour makes quantitative analysis and recovery from tested feeds extremely difficult. Frequently the aroma of a flavour is the major quality criterion used. This also makes legislative control of flavour quality and flavour ingredients difficult.
( 6 ) Flaoour perfbrmance. Animal response trials with flavours are time-consuming and expensive to conduct. From the commercial or marketing aspect, flavour performance may simply be its persistence after pelleting or during storage of feed, which can be readily ascertained.
Feed flavours are only one class of feed additive and must be selected and utilised in conjunction with other additives for maximum benefit.
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Enzymes as Feed Additives
Andrew Chesson, Claire N Bedrock, Eoin N Cowie and Peter M Hotten
Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB, UK
The primary function of the enzymes under study as non-ruminant feed additives is the breakdown of plant cell-wall polysaccharides to monomeric or low molecular weight oligomers capable of being absorbed in the upper digestive tract of pigs and poultry. Such an approach may increase the range of feed ingredients suitable for inclusion in diets, as well as improving the utilisation of current diet components. Other possible benefits include the release of protein and storage polysaccharide otherwise protected by intact cell walls, the specific destruction of anti-nutritional compounds and the improved utilisation of some legume proteins.
Because of the complex nature of cell-wall polysaccharides, any enzyme-based feed additive must contain a large range of activities with different specificities. The activities necessary and their relative proportions will be defined by the chemical nature of the feed ingredient or compounded feed. However, as most plant feedstuffs differ only in the proportion of the various polysaccharide types contributing to the cell wall, substantially different enzyme preparations are unlikely to be necessary. The required physical properties of the enzymes present in a formulation will be defined by their major site of action and proposed mode of delivery to that site. The temperature stability of an enzyme may be a critical factor determining its ability to withstand pelleting, for example. In this respect it is unfortunate that most commercially available enzymes derive from strains of relatively few mesophilic organisms, which limits the range of enzymes available with markedly different physical properties.
In-vitro screening of enzymes for their biological and physical properties can reduce, but not replace, the need for time-consuming and expensive in-viuo experiments. In this laboratory, enzyme mixtures are continually being refined by analysis of both solubilised and residual carbohydrate obtained from in-uitro digests of selected feed ingredients under appropriate conditions. The molecular weight distribution of solubilised sugars is monitored by HPLC and the results are used to modify the glycosidase content of the mixture to ensure maximum monosaccharide production. The glycosidic linkage pattern of the insoluble residue is determined by methylation analysis and compared with the pattern shown by the original substrate. Recovery from residues of any partially methylated sugar derivative in amounts relatively greater than that initially present suggests inadequate levels of the glycan hydrolase active against that particular linkage. In this manner deficiencies can be identified and enzyme formulations improved before in-vivo evaluation.
There is a significant difference between the gross energy and metabolisable energy content of most feedstuffs-whether measured in poultry or in pigs- the extent of which provides some indication of potential for improved feed utilisation. It is the function of added enzymes to minimise this difference. However, the
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ultimate commercial value of enzymes as feed additives depends on economic considerations. The decrease in feed cost resulting from improved utilisation must outweigh the costs associated with the enzymes leaving a margin of increased profitability for the compounder.
Product Registration and Legislation
J W Stoker
ELANCO Products Ltd, Dextra Cpurt, Chapel Hill. Basingstoke RG21 2SY. UK
Although legislation in the UK to control animal feedstuffs has been on the statute books throughout the 20th century, it is only since the appearance of the Medicines Act (1968) that legislation has developed to police the industry and safeguard the consumer.
Several Acts form a complex interlocking framework to control the many aspects of feed manufacture and feed additive usage. Part IV of the Agriculture Act 1970 requires that feedstuffs should be suitable for their intended use and free from toxic ingredients. Various regulations deal with sampling, methods of analysis, and labelling requirements for the display of feed composition.
The Medicines Act (1968) deals with the licensing ofmedicinal products under the headings of safety, quality and efficacy. Several other matters relating to animal feedstuffs are dealt with by various regulations under the Act. These include distribution, labelling, limits of variation of additives, methods of analysis and sampling and the incorporation of medicinal additives in feedstuffs.
The thrust of feed-additive legislation at both EEC and UK level is set towards increased control. Initially controls centred around the purity, safety and efficacy of the product. However, more recent legislation affects the application and use of the additive. The Animal Health and Welfare Bill 1984 introduced the requirements for registration of feedstuff manufacturers. Group A manufacturers must register by 1 July 1988 and Group B by 1 July 1989. Both groups will be subject to a Code of Practice. The requirements for Group A will be more stringent, and such manufacturers will be allowed to incorporate concentrated additives into feeds; Group B manufacturers may not include premixes with an addition rate of less than 2 kg t - ' of final feed.
Harmonisation of feed additive legislation in the EEC has probably progressed as far or further than any other agricultural legislation. Free sale feed additives are covered by Directive 70/424/EEC in relation to the list of permitted products, their usage and approved levels of active ingredient in the final feed. A more recent Directive, 87/153/EEC, deals with the information required for a product to be licensed under 70/524 and also provides for the production of a monograph providing member states with a description of the medicinal additive.
The ability of veterinary surgeons to write prescriptions either for products used outside the terms of the licence or unlicensed products has led to the introduction of Veterinary Written Direction product licences for certain well known active ingredients. Although the licences will have to supply data to cover the basic tenets
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of safety and quality, they will not have to supply such extensive efficacy data as a full product licence and, therefore, will have no therapeutic claim.
The use of unlicensed products even under veterinary prescription introduces the possibility of unacceptable residues for the consumer and raises the question of the safety of the animals and the handlers of the product. There are proposals from the MAFF to ban the use of unlicensed materials in food-producing animals once Directive 86/469/EEC comes into force in 1989 and extends the current UK pilot residue monitoring programme.
The next stage in the provision of protection for the consumer is control at farm level. A Code of Practice for the safe use of veterinary medicines on farm was introduced in 1985 together with the requirement for an Animal Medicine Record, and it is possible that statutory record-keeping requirements may be introduced when Directive 86/469/EEC is implemented.
Once this has been achieved, the use of feed additives will be subject to controls at all stages of their use: production, authorisation, incorporation and farm level.
The Requirement for Additive-free Meat --Implications for Feed Compounders
Dalgety Agriculture Ltd, Dalgety House, The Promenade, Clifton. Bristol BS8 3NJ, U K
During the last five years three published reports, namely those of NACNE (1983), COMA (1984) and the BMA (1986), have focused attention on diet-related health problems. As a consequence some members of the public have shown a greater interest in the composition and nutritional value of foods that they consume. One aspect that has caused a great deal of public concern is the subject of food additives or E numbers, and the allergic reactions to these. Food manufacturers now offer products free of many artificial additives, such as antioxidants, colourants and preservatives. Confusion exists between food additives and animal feed additives. This is often the result of presentation by the media being based more on the emotive issues than on stating the technical facts.
The main concern regarding animal feed additives is the potential for tissue residues. There is now a demand for food products to be healthier and produced by farming systems considered to be more natural or without feed additives. In general this applies more to pig- and poultry-meat products and to eggs than to beef or lamb.
The current size of the market for additive-free meat is relatively small, approximately 0 1 % of the total meat consumption in the UK, but it is predicted that this will increase to 3-5% by the early 1990s. Developments are occurring rapidly in other countries. In the USA 40% of turkeys and 25 % of broiler chickens are produced in farming systems that allow them to be labelled as being residue-free meat, and in France 15% of all poultry is labelled as being produced in a natural and traditional way.
The licensing authorities in the UK and EEC ensure that any medical feed additive is safe and beneficial to the animal, and is not harmful to the public and the
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environment. Medicinal feed additives are classified as PML (Permitted Merchant List) or POM (Prescription Only Medicines). The PML additives includes the growth promoters which, since they are only active within the gut, do not (contrary to public belief) give rise to tissue residues and do not require a withdrawal period before slaughter. The POM additives are under veterinary control, require a Veterinary Written Direction, are normally for therapeutic use only, and usually need a withdrawal period.
Removal of a growth promoter from a feed, without any other dietary manipulation to compensate, can result in poorer growth rate and efficiency of feed utilisation. This will increase the cost of meat production. Alternatively nutrient specifications of diets can be increased to replace the growth-promoter effect, but the animal feedstuffs will cost more.
Additive-free animal feedstuffs means additional product lines at the feed mill. The need to maintain identity with regard to POM, PML and additive-free products requires more down-time in terms of production and more frequent flushing within the plant. All this increases production costs, which must be passed on to the consumer and therefore fully recovered from the marketplace.
References British Medical Association (BMA) 1986 Report 011 Diet, Nutrition and Health. British
Medical Association Publications Department, London. Committee on the Medical Aspects of Food Policy (COMA) 1984 Diet and Cardiouascular
Disease. Report on Heulth and Social Subjects, 28. HMSO, London. National Advisory Committee on Nutritional Education (NACNE) 1983 A Discussion Paper
on Proposals for Nutritional Guidelines jo r HeaM Education in Britain. Health Education Authority, London.
Recent Developments in Coccidiosis Control
N J Lodge
Roche Products Ltd, PO Box 8, Welwyn Garden City, Herts AL7 3AY, U K
Coccidiosis is a ubiquitous disease in the poultry industry: heavy coccidial populations will build up quickly, even in brand new sheds. The poultry industry itself has expanded rapidly over the past 50 years. Arguably anticoccidial development has played a major role in this increase.
Recent developments in coccidiosis control can be summarised as follows:
1 Realisation that few medicinal products have been developed Costs of development are extremely high and the time scale between patenting and marketing a product is nowadays well over 10 years. Hence few new products are under development. The ionophore group of additives represents the most significant recent advances in coccidiosis control.
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2 Awareness of developing resistance The high turnover rate of a coccidial population results in a relatively quick development of resistance. This can occur rapidly with the older synthetic chemical compounds but is a slow process with the ionophores. Cross-resistance between ionophores is a significant factor.
3 Use of shuttle and rotation programmes Judicious use of currently available products is essential to extend the life of these additives. Shuttle programmes, with the use of two or more products within the life of a flock of birds, represents one solution.
Rotation programmes, in which a product is used for three to seven crops of birds, represents a more satisfactory long-term coccidiosis control programme. Anticoccidials are exposed for a limited period of time and hence less chance exists of development of resistance. Ideally products with a dissimilar mode of action should be used alternately in such a programme.
Potentiation of existing products (eg use of two products with a different mode of action) is currently being investigated.
4 Awareness of toxicity It has been well reported that certain products are highly toxic to non-target species such as turkeys and horses. Crosscontamination can occur in even the best feed mill, although recently produced Codes of Practice have reduced this risk. Incompatibility of anticoccidials with other medication programmes has also to be borne in mind.
5 Consumer awareness A vociferous lobby exists which argues against the use of any routine in-feed medication. This is presented on a non-scientific basis, yet the lobby tends to achieve increasing media coverage. Supermarket prices demand intensification of the poultry industry, which in turn demands routine coccidiosis control.
6 Development of vaccines This exciting new aspect of coccidiosis control can be achieved by two methods: (a) by injection of immunogenic coccidia antigens; (b) by delivery of attenuated precocious strains of coccidia or low doses of virulent coccidia. Live vaccination is being developed for in-feed delivery via beadlets. Extremely low doses per beadlet have been developed and hence an accurate dose of live pathogens can be achieved. This method of vaccination is in the development stage, and many problems remain to be solved, eg cross-protection between species, age of immunity development and consumer acceptability.
It is clear that vaccination in whatever form will not be available in the near future. Hence judicious use of existing and newly developed products is essential.
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Peter J Buttery
Department of Applied Biochemistry and Food Science, University of Nottingham School of Agriculture, Sutton Bonington, Loughborough LE12 SRD, U K
Beta-agonists have been known to the pharmaceutical industry for many years, largely as safe methods of treating asthma. Recently, however, they have found their way into animal production studies following the recognition that, when given orally to most mammalian domestic livestock, they cause a dramatic reduction in carcass fat together with an increase in lean. At appropriate doses they may increase liveweight gain, although the magnitude of the response is not usually as large as was seen with anabolic steroids. The responses in cattle, sheep and pigs appear to be of a similar magnitude. There is little evidence for an interaction with sexual status or with whether the animal has a functioning rumen or not. The responses seen with poultry are much smaller and there is some evidence that it is dependent on the sex, but this may only be related to differences in the tendency to deposit fat.
The compounds that have been reported in the literature to be effective repartitioning agents tend to show specificity towards the beta-2 receptor. Receptors can be divided into alpha and beta and the beta receptors further into beta-1 and beta-2 types. Evidence suggests that white adipose tissue has a distinctive beta receptor. Beta-agonists cause a reduction in lipogenesis and an increase in lipolysis, and this is probably how they cause a reduction in body fat. Muscle tissue contains beta-2 receptors, and these can be demonstrated on muscle cells in culture, ie muscle tissue without the possibility of contamination with such things as fat cells or vascular tissue. Beta-agonist treatment reduces muscle protein breakdown and there are suggestions that it also causes an increase in muscle protein synthesis. Although there are receptors in muscle which bind beta-2-agonists, there remains doubt as to whether these agents act directly on muscle. Evidence using muscle cells in culture has been equivocal. As with most interventions using hormones or their analogues in animals, beta-agonist treatment causes changes in the circulating concentrations of other hormones, for example insulin. Beta-agonist treatment also reduces the number of cytosolic glucocorticoid receptors (unpublished observations from this laboratory). The possibility that beta-agonists cause muscle hypertrophy in part by altering the insulin-glucocorticoid status of the animal requires further investigation as do several other suggestions on the mode of action of beta-agonists.
The treatment of animals with beta-agonists must be shown to be safe for the consumer as well as not inducing undue stress on the animal. The published evidence would indicate that these two ideals are likely to be fulfilled. The eating quality of the meat must also be considered. There have been reports that meat from treated animals may be slightly tougher, but this appears to be dose related and may turn out to be of little practical relevance. On the evidence publicly available, beta- agonists offer a way of humanely and safely producing leaner meat and therefore of helping to achieve the ideal of reducing the fat intake of man.