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