The preparation of the introductory paper to this Conference has presented two particular problems. First, as always, there was the risk that it would contain too many references to aspects which would be dealt with in greater detail — and possibly contradicted subsequently. Secondly, the title of the Conference, ‘By-Products and Wastes in Animal Feeding’, seemed to be at variance with a definition of waste, ‘a resource arising (in agriculture) where the cost and complexity of using that resource is greater than the returns from using it’, which I had used at a similar Conference a year ago (Raymond, 1977) and which might imply that ‘waste’, once utilized, is no longer ‘waste’. But this is really semantics; the aim of this Conference is to bring together the latest information on whether resources which have conventionally been considered ‘wastes’ can effectively and economically be utilized in new animal feeding systems. The concept of economic use is vital. I strongly believe that we must reject the idea that there is some sort of moral imperative to use wastes; if this is not economic then their use must involve the misuse of some other resource within the total production system.

The situation is of course dynamic; effective research and development (R and D) can transform yesterday's waste resource into a new productive asset. Further, the economic environment is not static; for example, changes in relative costs of feedstuffs mean that farmers will this winter feed large quantities of straw which in 1972 they would have burnt in the field, while high cereal prices mean that more non-tariff components, including by-products, are now being included in least-cost livestock rations. Thus it is worth examining some of the factors that have led to the current interest in the role of by-products and waste materials in animal feeding setting aside any marginal objection to this use of ‘waste’.

To use information means to use the experiences of others to make decisions. In fields where experience is lacking it can be gained by conducting experiments. People who have available experience in a special field are called experts. In each field of economics production is subject to changes of several factors such as price and availability of the raw material needed for the special type of production. Animal production depends mainly on the availability and prices of useful feeds, and should be regarded as one type of production among others, the different types being more or less correlated.

From time to time changes in industrial or other types of production occur. New materials, often regarded at first as worthless wastes, may be found to be suitable as feeds, but thousands of tonnes of such a new material may have been destroyed before its feed value was established. In other cases the new material may have been given to animals but without success, causing illness or reducing efficiency. The reason for the failure may be that no previous experience was available, no experiments had been made previously or were known and no expert could be asked. In other words, no information was available about the nutritional value of the specific material.

The situation of deficiency of information is comparable to the situation of deficiency of feeds. If regular feeds are not available in adequate quantum or at acceptable prices, then interest in the use of by-products and wastes increases. If no results from research in that specific field are published and no experience is available, one has to look for ‘by-products’ of knowledge. Anybody anywhere in the world may have analysed a sample of a feed for a specific purpose. The result may have been forgotten after the particular question had been answered. But perhaps some years later this piece of knowledge could be used for a quite different purpose. The experience of others then becomes valuable.

The increasing awareness of the potential use of by-products and the recycling of waste materials, etc., presents the nutritionist with new and interesting challenges. There are several reasons for this. First, that many waste and by-products, hereafter referred to as waste suitable for animal feeding, are produced in small quantities in differing localities; often availability is very seasonal and composition varies enormously. As a result there may be some reluctance both on the part of producers and government organizations to invest a great deal in a research programme of evaluation. Secondly, the motive of industrial producers for using organic wastes for animal feeding is more often a desire to obtain a positive return by selling wastes rather than paying for their disposal, than a real interest in meeting the requirements of the animals. As a result wastes are often produced with dangerous contaminants which could have been avoided.

In many instances, therefore, nutritional advice on the use of waste in animal feeding has to be based on a knowledge of similar known feeding-stuffs and a minimum amount of analysis for basic nutritional qualities and for possible dangerous contaminants. These statements are, however, generalizations as some material, like excreta, are of variable quality and produced in vast quantities. I shall attempt to discuss briefly the nutritional attributes of different classes of waste since they are to be discussed more in detail by others at this meeting. First, a division will be made into mainly nitrogen (N) and mainly energy-yielding products and secondly the feeding systems in which they can most profitably be used will be discussed.

The livestock population of Great Britain has been free from several of the most serious epidemic diseases since the late 19th century (rinder-pest, contagious bovine pleuropneumonia); others occur infrequently following introduction from abroad (foot-and-mouth disease (FMD), swine fever, swine vesicular disease (SVD); and the endemic diseases such as bovine tuberculosis and brucellosis are subject to successful eradication programmes.

On first examination the risk from exotic disease appears to lessen from year to year. The incidence of FMD has declined dramatically in Europe with the introduction of effective vaccination and slaughter policies and FAO/OIE programmes creating protective vaccination buffer zones in the east. Again within the European Community consideration is being given to a common policy to eradicate swine fever from all member States. However, a number of factors operate against these encouraging trends.

a. The relaxation of international trade barriers to the movement of live animals and animal products. It is essential within this framework to ensure that our animal health safeguards are preserved as far as possible against the introduction of disease from either member States or into the Community from third countries.

b. Pressures from the industry increase for the importation of livestock, semen or embryos to expand the gene pool within breeds.

c. The pyramidal structure of the industry — particularly the pig and poultry industry — increases the risk of dissemination of any disease agents introduced.

d. Larger, more intensive units reduce individual animal observation allowing symptoms of disease to remain undetected for longer periods and hence outbreaks to be more explosive when they occur.

The most widely-quoted estimates of straw supplies and usage in England and Wales are those of a working party of the National Farmers Union (1973). They assumed the yield of straw to be 2.8 t/ha, and hence 9.3 Mt from 3.4 M ha of cereals in 1972. (The same yield from 3.7 M ha of cereals in the UK would give 10.4 Mt.) Of the 9.3 Mt, 37% was estimated to be burned in the field or ploughed in, 36% used for bedding, 15% used for feed, and 12% used for other purposes. The figure of 2.4 t/ha (1 t/acre) may well be too low. Short (1974) found straw yields at four Experimental Husbandry Farms over several years to be as follows (t/ha): winter wheat 3.71, spring wheat 4.68, spring barley 2.71, and spring oats 4.54. Wood (1974) surveyed wheat crops in Oxfordshire in 1973 and found yields of 3.7 t/ha. The total quantity of straw available is therefore likely to be considerably in excess of 9.3 Mt and could if necessary be increased further by cutting at a lower level. The accuracy of the National Farmers Union estimate of 0.15 × 10.4 = 1.6 Mt used for animal feeding is also questionable, but this amount would — if it contained 6.5 MJ metabolizable energy (ME)/kg dry matter (DM) — be sufficient to provide only about 7% of the maintenance requirements of all cattle in Britain. On a larger scale, Balch (1977) has calculated that if all the straw grown in Europe were improved by chemical treatment it could provide 80 to 90% of the maintenance requirements of Europe's ruminant livestock. World estimates for the production of straw and other fibrous wastes are given by Owen (1976).

In Agricultral Statistics, United Kingdom, 1974, the area of land devoted to vegetables grown in the open for human consumption is given as 187 500 ha. This amounted to some 4% of the tillage land in the UK, and along with similar areas of sugar beet and maincrop potatoes would appear to offer significant scope for the utilization of associated by-products as feed for livestock. The range of such crops produced in the UK is quite wide, but climatic and market pressures will influence actual cropping from year to year. Relevant details for the United Kingdom are set out in Table 1, and it will be seen that in 1974 England and Wales accounted for 95, 78 and 100%, respectively, of the areas of outdoor vegetables, maincrop potatoes and sugar beet grown in the UK. In the following, therefore, the discussion will be concentrated on the problems of production and distribution of vegetable and arable by-products. Similar problems of distribution will no doubt occur in other countries as well.

The recycling of nutrients from animal excreta has occurred naturally for a very long time. For centuries scavenging pigs and poultry consumed undigested grain from cattle manure. More recently, however, interest in large-scale recycling of animal manures has arisen from a need to reduce the problems of pollution associated with large, intensive livestock units. To date the development of the use of animal excreta as feeds for livestock has been largely confined to those countries in which many thousands of livestock are kept on relatively small areas of land, for example the beef feedlots of the USA.

The trend towards increased size of livestock unit is universal. In England and Wales the number of large livestock holdings increased three-fold in the period 1967 to 1977 (Table 1). There is little doubt that this trend will continue, as farmers strive towards achieving greater economies of scale. In consequence, there is increasing need to develop methods to utilize the manure produced from large livestock units in ways which do not give rise to environmental pollution.

From just five industries in the United Kingdom — brewing, distilling, milling, sugar extraction and potato processing — at least 2.7 × 106 mega joules (MJ) of metabolizable energy (ME) and 4 × 105 tonnes of crude protein (CP) are available annually to livestock farming as by-products. This is equivalent to 1.6 × 106 tonnes of barley and 4.7 × 105 tonnes of soya bean meal, although in some cases nutrient density may differ somewhat from that found in barley or soya.

A large proportion of the by-products available is already used in animal feeds, either djrectly by the farmer or through inclusion in compound feeds which are then used as components of balanced rations.

The materials available are potentially alternative feedstuffs to conventional forages or concentrates. As such they will only form part of a balanced ration and it is in this context that their relative value and usefulness can be judged. In many investigations there has been a tendency to consider particular by-products in isolation and as a consequence any nutrient imbalance has been highlighted to the detriment of the material as an alternative feed. Very few straight feedstuffs contain ratios of nutrients balanced for particular levels of animal production and invariably rations for livestock consist of blends of different materials. Whilst extremes of nutrient imbalance may be identified in individual by-products they are, none the less, wholly suited to blending with other by-products or feeds of contrasting nutrient content in order to produce a completely balanced ration.

For the purpose of this paper I intend to include within the term ‘by-products’ all those materials that arise from the food industries which are not consumed by the human population of the United Kingdom. Some of these materials are not acceptable as part of the human diet, or, if acceptable, find no ready market. Other materials are inedible, perhaps by humans and other animals, but can be converted into acceptable food or feed whilst yet others which are edible and acceptable are wasted in processing, storage, transport, distribution and in the kitchen and dining room. It is impossible to give a figure for the annual amount of by-products and waste available but statistical evidence points to approximately 6 million tonnes of food, all of which is edible but not consumed. This figure does not include by-products which are not intended for human consumption such as abattoir wastes, whey and brewery wastes and cereal offals. The total figure is therefore larger and represents a considerable potential economic resource. (It must be observed however, that only a small fraction of these wastes and by-products can be economically utilized. Other speakers are dealing with animal slaughter, fish and cereal wastes and I will therefore give only passing attention to these materials.)

About 40 million gallons of cheese whey are produced in the UK each year on the farm. Of this, about 12 million gallons are fed directly to pigs. Although it appears that heavy hog production and cheese making are often associated, disposal of whey on farm remains a problem, since the price fetched by whey may be only a quarter or less than the cost of transport. Disposal on land, where it can be useful as a fertilizer, can lead to pollution problems. Trials carried out by ADAS (Wolverhampton) on both beef and dairy cattle are promising. It has been shown that every kg of barley previously fed to dairy cattle can be replaced by 10 litres of whey at half the cost, making barley feed unnecessary. In diets for steers, calculations have shown that a litre of whey at 6% solids can replace 90g of compound for energy (Peacock, 1977).

The slaughter of animals for human consumption leads to the production of a large quantity of materials which with further processing can be converted into a form suitable for use in animal feedingstuffs. Currently, much of this material goes to waste because of the fragmentation of the abattoir industry into many small units (1700). This means that it is often uneconomic to transport by-products to central points for further processing. However, more stringent control of effluents from abattoirs and the need for high capital investment to bring units up to newly imposed standards means that slaughterings will be concentrated into fewer and larger units (250) (Gerrard and Mallion, 1977), so making the collection and further processing of waste more attractive from both the economic and environmental standpoint. Within the UK, some 13 to 13.5 million cattle units are slaughtered per year (Table 1). (1 cattle unit = 1 beast or 2 pigs, or 3 calves, or 5 lambs).

Most of the by-products from fish go into the production of fish meal and fish oil, the latter going directly to the human food chain, and therefore do not really come under the heading of industrial by-products and waste per se. Broadly speaking, fish meal made from fish offal is a by-product which otherwise would have been wasted. This paper discusses the quantities involved and the nutritional properties offish meal, and in addition, the contribution to fish meal and fish oil made from species which are not suitable for human consumption (e.g. sandeels) or where the quantities caught exceed the demand for human consumption (e.g. sprats).

Any method of utilizing fish by-products for animal feeding should minimize chemical changes in the product to avoid reduction in the nutrients which are present at the time of catching. In some respects chemical changes in fish by-products are brought about in a similar way to those in grass, cut for preservation. The fish material has a high water content, around 75%, and from the time of catching is subject to chemical changes by enzymes in the fish and also by bacterial action. Fish, however, differs from grass in that it contains oil and virtually no carbohydrates. The demersal, or lean fish, for example, cod, haddock, plaice, saithe, etc., contain high levels of oil in the liver which are removed for separate processing, but little in the flesh and in the offal produced. The ‘industrial’ fish caught are mainly pelagic species with high levels of oil in the flesh.

This paper discusses the composition and nutritional values of a limited number of materials of tropical or sub-tropical origin encountered in advisory work. These products have emerged in recent years chiefly as minor components of compounds and to a lesser extent as ‘straights’. These by-products are olive pulp, grape pulp pellets, grape seed meal, dried coffee residues, citrus pulp pellets, cocoa shell meal, extracted cocoa meal, shea-nut pellets and shea expeller meal, guar meal, illipe meal and cassava meal. Other foods such as cereal by-products and sugar cane molasses are discussed elsewhere, whilst materials that may originally have been by-products of oil extraction such as soya, ground nut and palm kernel, etc., are now such significant parts of the modern sophisticated feed compounding industry that it may be unfair to classify them as by-products in the usually accepted sense. In any case information on them is well documented and readily available and hence they will not be discussed here.

The by-products listed above form only a small proportion of the imported feeding stuffs bill but nevertheless can be of economic and nutritional significance in isolated circumstances. Some idea of their overall monetary significance is as follows. The total quantity of imported feeding stuffs other than cereals in 1977 was 1 495 973 tonnes. Of the above list of by-products, only olive pulp and grape residues are listed separately on official lists and each account for less than 1% of the total. Olive pulp imports were 33 457 tonnes and grape residues 11 276 tonnes. Undefined residues from oil extraction, which presumably includes some of the above listed products, amounted to 58 791 tonnes, whilst ‘Other products of vegetable origin’ would account for some other imported products totalling 45 013 tonnes.

Over the last 30 years there has been spectacular growth in the UK broiler industry (Richardson, 1976), intensification in the UK pig industry and a move to larger herds and higher yields in the cattle industry. These trends have meant that farmers have bought more livestock feed both as compounds and as straights. Parallel to these changes, the move from ‘target’ to ‘least cost’ formulation by the compounder and computerized home mixer has increased the ability to deal with different raw materials and to utilize these successfully in compounded diets (Wilson, 1975).

In spite of all these technical advances, livestock still depend on large quantities of cereals and other raw materials which are potential food for man (Wilson, 1977) as illustrated in Table 1. This is in spite of the fact that, over the past 15 years, the general trend-line in the ‘carry over’ stocks of world grain has been downwards (Brown, 1977). It follows that, in considering future feeding policies for livestock, there are good reasons why prudent steps should be taken to find and utilize alternative sources of both energy and protein for animal feeds. Holland has been more successful in this respect than the UK (De Boer, 1978) as instanced by the increasing imports of cassava which in part replaces European-grown barley and wheat (Walters, 1978).