GB1604382A

GB1604382A - Preparation of feedstuffs for minute aquatic animals

Info

Publication number: GB1604382A
Application number: GB16087/78A
Authority: GB
Original assignee: Unilever PLC
Current assignee: Unilever PLC
Priority date: 1978-05-31
Filing date: 1978-05-31
Publication date: 1981-12-09

Description

(54) PREPARATION OF FEED STUFFS FOR MINUTE AQUATIC ANIMALS (71) We, UNILEVER LIMITED, a British company, of Unilever House, Blackfriars, London E.C.4, England, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to the preparation of feedstuffs for minute aquatic animals, such as the "first feeding" or larval stages of certain fish, crustacea and mollusca, which require their diet to include granules having a maximum dimension of less than 300 microns.

The prospect of rearing marine fish species such as turbot, sole, halibut and sea bass in captivity on a commercial scale is very attractive. However, a major stumbling block has been the production of an artificial diet acceptable to the larvae of such fish, to replace the live food organisms which are currently used. The previous reliance on live foods in the early rearing stages of these fish is undesirable, because the live food organisms are themselves expensive to produce, and their nutritional characteristics are difficult to control. Unacceptably high mortalities have been observed when a transition from live to artificial food has been attempted in captivity on an experimental basis. The most commonly used live food for rearing marine fish larvae is the brine shrimp Artemia, of which the smallest are about 250 microns in diameter.

Clearly an artificial "first feeding" fish feed for the larvae of a given species must include granules of a size that the larvae can ingest: this is dictated by the mouth gape of the creatures. For "first feeding" turbot larvae, a fish feed should include granules in the range 50 to 100 microns. For sole and halibut larvae the optimum range is 100 to 250 microns.

The unsatisfactory nature of artificial feedstuffs which have been tried in the rearing of fish larvae to date can be attributable to two distinct causes: poor overall formulation either in nutritional or taste terms, and poor physical properties such as non-uniformity of composition or inappropriate behaviour in water. Any such defects, if severe, can render the feedstuff quite unacceptable to the larvae. The problems associated with producing a feedstuff having an overall formulation suitable for any given species of marine larvae are immense, and in the context of the present invention we do not claim to have made any advance on this front. The present invention is converned solely with the production of feedstuffs of which the individual granules are physically more acceptable to the larvae.

Conventionally, artificial feedstuffs for fish are prepared by pelleting, crushing and screening a blend of ingredients. Unless the individual ingredients of the feedstuff are milled very finely prior to pelleting, it is likely that the crushed pellets, usually referred to as crumbles or granules, will not have a uniform composition because there is a tendency for the pellets to break down into the primary particles from which they were made. In the crushing operation there can be little or no control over the size range of the granules produced and thus much material has to be recycled, or is wasted, following screening. Due to the inherent non uniformity of such feedstuffs, there is considerable risk that a larvae will ingest a particle consisting solely of a single constituent of its diet. For example, a large mineral crystal, which might survive intact in the conventional process for making artificial fish feeds, could provide a fatal overdose if a tiny larvae were to ingest it. Moreover, it is believed that a larva does not continue to feed if it encounters unpalatable particles of feed, and thus compositional uniformity is also essential if a good feeding pattern is to be established.

A further essential attribute in an artificial feedstuff for fish larvae is that the feedstuff granules must readily wet out and disperse when placed in water, so that the individual granules become accessable to the larvae. If the granules have a strong tendency to remain as aggregate, too large to be ingested by the larvae, the feedstuff will be wasted and a severe risk of pollution of the larva 5 environment can occur. It is believed that such pollution has been a further problem which has hitherto hindered the use of artificial feedstuffs in this field.

A further preferred attribute is that, where appropriate for the species concerned, the individual granules should sink in water rather than remain in the surface film.

In British patent specification No. 1,226,799 there is described a method of manufacturing feedstuffs in the form of spherical granules having diameters in the range 1000 to 6000 microns by the steps of delivering a particulate ground food material onto a supporting surface of a rotating support element inclined to the horizontal plane at an angle in the range 30 to 50 degrees, and spraying a liquid (water, perhaps containing micro-additives or vitamins) onto the particulate material located on the surface of the support element so that the particulate material is subjected to granulation. The principal advantage claimed for the process as described is that it leads to greater compositional uniformity, and in particular that microadditives and vitamins are evenly distributed in the granulated feed. It is undoubtedly true that the process as described in British patent specification No 1,226,799 should lead to greater compositional uniformity in large granules than the conventional process already described above. However the process as described does not apparently provide granules having a diameter less than 1000 microns.

The granulation technique utilised in the process described in British patent specification No. 1,226,799 is an example of the procedure commonly referred to as pan granulation or disc pelletising. The essence of such a procedure is that a tumbling bed of finely divided substrate is sprayed with a liquid, and the continued tumbling motion of the moistened substrate particles causes the particles to agglomerate into granules. A typical pan granulator is a right cylindrical vessel open at one end and rotatable about the axis of the cylinder, which axis is generally held, during operation, at an angle of 20 to 40 to the horizontal such that the open end of the vessel is uppermost. The pan is charged with finely-divided particulate substrate, which forms a tumbling bed of powder when the pan is rotate. In a typical pan granulator the speed of rotation of the pan can be varied, stepwise, from about 10 rpm to about 50 rpm. The pan can be fitted with internal baffles which affect the tumbling motion of the substrate. Similar granules can be prepared in a drum agglomerator, in which the agglomeration of a finely divided moistened substrate is achieved while the substrate forms a tumbling bed descending a rotating elongate inclined cylinder Despite the undoubted advance in the art which the procedure described in British patent specification No. 1,226,799 represents, namely helping to solve the problem of compositional uniformity found in conventional feedstuffs having granule sizes up to 1000 microns and greater, we have found that when the simple concept of manufacturing a feedstuff in a moistened tumbling bed of substrate to produce rounded granules is applied to the manufacture of a feedstuff having a granule size appropriate for fish larvae, neither the process nor the product so formed are satisfactory. The use of water alone as the agglomerating liquid leads to an undesirably high spread of sizes in the granulated product, which renders the process inefficient in terms of the yields of granules in the size range required. Further, the behaviour of the resulting granules when placed in water can be far from satisfactory.

The present invention provides a process for the preparation of a feedstuff for minute aquatic animals which require their diet to include granules having a maximum dimension of less than 300 microns, in which process a bed of finely-divided essentially solid feedstuff ingredients, having a mean particle size not greater than 150 microns, is tumbled in a pan granulator and the tumbling bed is granulated by spraying thereon an aqueous solution of a non-toxic polymeric material, the granulated product so formed is dried to a moisture content of less than 15% by weight, and the granulated product is physically classified to ensure that it contains more than 10% by weight of granules having a maximum dimension of less than 300 microns.

The use of a pan granulator leads to the production of granules that are predominantly spherical in form, in other words although it is unlikely that many of the granules will be truly spherical, nonetheless few, if any, of them will have any significantly angular surfaces and thus at least the bulk of the granules will have a wellrounded cross-section in every dimension.

The process of the invention also leads to a substantially uniform composition in the individual granules. When a feedstuff comprises such small granules prepared from several ingredients, it is clearly unrealistic to expect that every single granule will contain every ingredient, and especially every ingredient in the proportions in which such ingredients occur in the feedstuff as a whole. Nevertheless, it is possible to use the invention to prepare a feedstuff in which at least 50% by weight of the granules individually contain each major ingredient of the formulation. Thus at least 50% by weight of the granules individually represent a "mouthful" of feed in which is not totally unbalanced. Preferably at least 70% and ideally at least 90%, by weight of the granules individually meet this requirement.

It will be appreciated that in order to fabricate a granule of substantially uniform composition and small diameter, the particle size to which the individual solid components of the substrate should be subdivided needs to be very much smaller. Ideally, the individual components of the substrate should be used at an average particle size not exceeding 35% of the mean granule size required in the feedstuff. When the individual components of the substrate cannot be purchased ready-milled to an appropriate particle size, they should be milled prior to use. Commercially available fine milling equipment, such as a swing hammer mill, is quite suitable for this operation. Preferably the mean particle size of the ingredients in the tumbling bed is not greater than 100 microns, and ideally not greater than 50 microns.

The non-toxic polymeric material which is applied to the tumbling bed via the sprayed aqueous solution is a key feature of the invention, as we have found that it plays a major role in the production of good yields of small granules within the size range required. Edible gums of animal or vegetable origin can be used, but the nontoxic polymeric materials can also be, for example, proteins which would not usually be regarded as gums: casein is a good example. Preferred gums are gelatins, and edible water-soluble polysaccharides such as alginates, particularly sodium alginates, but other gums such as guar gum, locust bean gum and gum arabic can be used. Alternatives are: starches and degraded starches such as dextrins, and substituted celluloses such as carboxyalkyl celluloses, e.g. sodium carboxymethyl celluloses, and alkyl celluloses, e.g. methylethyl celluloses and methylhydroxyethyl celluloses. Water-soluble synthetic polymers, such as polyacrylamides, polyacrylates, polyvinylalcohol and polyvinylpropylene can also be used.

It will be appreciated that all of these commercially available polymeric materials can be obtained in a range of molecular weight, and that their aqueous solutions can have very different viscosities. Hence it is not possible to give definitive concentration range in which these material should be present in the aqueous solution used to agglomerate a feedstuff of the invention. At one extreme, of course, the viscosity of the aqueous solution should not be so high that it is impossible to spray it under practical operating conditions. The minimum concentration, on the other hand, is dictated by the requirement that the polymer should be present in sufficient quantity to give rise to a discemable effect on the particle size distribution of the granulated product. It will be self-evident to any skilled reader that the setting up of a process in accordance with the invention will necessarily involve a number of trial runs, and this will include a check on th optimum concentrations at which the particular polymer chosen should be used. However, as a guide, we have found that for gelatins and casein the concentration in the aqueous solution will generally need to be at least 2%, and usually not more than 15% by weight, and a typical operating range for these polymers will be 510% by weight. For sodium alginate the concentration will generally be at least 0.1%, and usually not more than 1.5%, by weight, with an optimum range of typically 0.51.0%. For sodium carboxymethylcellulose the concentration will generally be in the range 0.15% by weight. By way of comparison, for the synthetic polymers, such as polyacrylamides, an optimum range can be 30-200 ppm, typically 50-80 ppm.

The volume of the aqueous solution applied to the tumbling bed will generally be in the range 5 to 30%, preferably 5 to 15%, expressed by weight of the dry bed.

In general the aqueous solution can be applied to the tumbling bed at ambient temperature. However, for concentrated solutions of certain polymers, such as gelatin, which would set at ambient temperature, the solution should be maintained at a tem- perature above the gel point of the solution. For gelatin solutions, an operating temperature of about 600 C is ideal.

In addition to the non-toxic polymeric material, the aqueous solution that is applied to the substrate can contain one or more minor components of the feedstuff, such as vitamins or medicants.

The aqueous solution is applied to the substrate in the form of a spray of very fine droplets. The aqueous solution should be fed at high pressure to a spray nozzle directed onto the tumbling bed of substrate particles. Different spray nozzles obtained from different manufacturers will probably need to be operated at different working pressures, and no specific advice can be given on this point. However, in general the working pressure will lie in the range 20 to 100 psi.

Typically, after the aqueous solution has been applied to the substrate and an adequate degree of granulation has been achieved, the water content of the granulated feedstuff will be of the order of 10 to 35% by weight. Where necessary, the granulated feedstuff should preferably be dried to a water content of not greater than about 12%, ideally not greater than about 10%, by weight, to inhibit the growth of moulds and other microorganisms during storage. Drying should be conducted under mild conditions, so that proteins and other delicate ingredients in the feedstuff are not unduly affected. During the granulation, and especially during any subsequent drying operation, the temperature should be kept as low as possible to prevent undue denaturation of the protein content of the fish feed. Temperatures not exceeding about 60O C, and preferably not exceeding about 500 C, should be aimed for. With this proviso, the techniques used for drying are not critical.

The substrate in the tumbling bed can be any combination of the essentially solid materials normally incorporated in fish feeds. These are described in detail below.

In addition, a strictly limited amount of any oily component can be present in the substrate if desired, provided that the overall liquid level in the substrate prior to granulation is not so high that the substrate will not form a freely-flowing bed when placed in the rotating granulator. In a preferred embodiment of the invention, however, where it is desired to include an oil in the feedstuff, the oil should be sprayed onto the tubling bed before the agglomerating solution is applied to the bed.

We have stated already that the present invention is not concerned with the composition of feedstuffs for marine fish larvae and other minute aquatic animals. Nevertheless, we envisage that such feedstuffs will be optimally formulated from combinations of ingredients which are used already in feedstuffs found to be suitable for larger fish which have been successfully reared in captivity on artificial diets. To this end, it is appropriate to indicate here the types of ingredients which are used in conventional feedstuffs for fish.

In general, feedstuffs for fish are characterised by a high protein content and by a substantial proportion of the energy source being oil. A typical fish feed can comprise, by weight, at least about 30%, preferably at least about 40% and generally not more than about 80%, proteins; up to about 40neo carbohydrate; up to about 20% oil; and a variety of minerals and vitamins together contributing up to about 15% of the fish feed.

Suitable protein sources include: fish meals, of which the most common in use are herring meal and anchovy meal; liver meal; oil seed meals, such as soya meal and cottonseed meal; single cell proteins and yeasts; blood meal; whey powder and skimmed milk powder; casein; gelatin; distillery by-products; and meat meal. Carbohydrates are generally present as cereals, such as: wheat germ meal, wheat bran and whole wheat meal; maize; barley; millet; oats; and rice. The oils used are usually: vegetable oils such as corn oil, soya bean oil and groundnut oil; and fish oils such as herring oil, capelin oil and cod liver oil. The usual mineral sources are bone meal, di-calcium phosphate and limestone. Sodium chloride and cupric sulphate are also generally present. In addition, a wide range of vitamins should be present, such as vitamins A, B1 (thiamine), B, (riboflavine), B, (pantothenic acid), B,2, C, D, E and K. It will be appreciated that the individual ingredients which are blended together to make up a feedstuff are often themselves complex mixtures, and thus can contribute to more than one of the above ingredient categories. It has already been mentioned that fish meal can contain oil. A carbohydrate source such as a cereai can contribute significantly to the total protein content of the feedstuff. Most natural ingredient will contribute some trace elements and vitamins.

After granulation of the feedstuffs, and drying as required to reduce its water content to less than 15% by weight, it will usually be necessary to physically classify the granulated product to remove any undue quantities of undersize or oversize granules.

In some instances it will be appropriate to divide the product into distinct size fractions.

A particularly useful embodiment of the invention is a feedstuff comprising rounded granules of substantially uniform composition, at least 40% and preferably at least 80%, by weight of which have a maximum dimension of less than 250 microns but not less than 45 microns.

The figures of 45 and 250 microns come from Standard Sieve sizes, which we have used for classifying our feedstuffs. It should be pointed out also that the manner in which the sieving is performed can affect the results obtained, and all particle sizes expressed in this specification relate to sizes as determined using Standard Sieves in the manner laid down in British Standard 1796 of 1952. Commercial sieving operations can lead to errors of up to 5% at least in the apparent sizes recorded. It should further be mentioned that, owing to the small quantity of feed required by aquatic animals of the size with which the invention is concerned, it is economic to produce and market a feedstuff in which barely 10% by weight of the total granules have a maximum dimension low enough to be ingested by the animals concerned. Ideally, however, the proportion of appropriately-sized granules is larger.

The following Examples illustrate the manufacture of granulated feedstuffs in accordance with the invention.

Example 1.

A substrate was prepared by blending the following ingredients in a standard Hobart* powder mixer: Ingredient % by weight Fish meal (oil content 9%) 68 Skimmed milk powder 13 Vitamin/mineral mixture 10 Edible oils 9 * Registered Trade Mark.

The fish meal and the vitamin/mineral had both been milled using a Mikropulatomiser No 5 mill such that 90% passed through a 45 micron screen, implying a mean particle size of less than 50 microns. The skimmed milk powder was purchased commercially and used unmilled as it was sufficiently fine already. During the blending, the free oil caused some agglomeration, and the lumps were sieved out.

5 kg of the substrate was loaded into a 50 cm diameter pan granulator, held at 30 to the horizontal and rotated at about 20 rpm. The substrate was sprayed with 0.7 litres of an aqueous solution, containing 5% by weight gelatin (120 Bloom grade ex Croda) and maintained at 60 C, using a Delavan-Watson WG 076 nozzle at a working pressure of 80 psi.

The granulated product was dried for 30 minutes at 50 C in a tray oven, to a water content of about 10% by weight.

A sieve analysis of the dried product gave the following result: Granule size (microns) % by weight ef product > 355 28.5 250-355 14.5 106250 44.0 43-106 10.0 < 45 3.0 The granulated product thus comprises a 44% fraction having a size range appropriate for sole and halibut larvae (106-250 microns) and a 10% fraction appropriate for turbot larvae (45-106 microns).

Uniformity of composition from granule to granule was inferred from microscopical examination.

Dispersion and rate of sinking were assessed by observing small amounts of the granules falling onto the surface of sea water in a beaker. Most of the granules wettedout and sank individually, very few agglomerates being seen; wetting out took about 10 seconds. The rate at which the granules sank was such that 0.25 g added to the surface of 1 litre of sea water in a 1 litre beaker produced a relatively constant level of granules in the body of the water for about 10 minute. Some material, mainly the smaller granules, remained on the surface and could only be sunk by agitation. This was not considered a serious problem, as some degree of agitation would normally be present in a rearing tank.

Thus it is clear that the invention represents a satisfactory method for preparing minute granules in reasonable yield and with good behaviour in water.

The physical acceptability to flat-fish larvae of the granulated feedstuff was demonstrated by feeding the 109250 micron fraction to dover sole larvae. Previously these larvae have only been successfully first fed in a captive environment using a living diet, usually the brine shrimp Artemis salina. Once the larvae have metamorphosed, i.e. assumed their characteristic fiat shape and become bottom rather than pelafic feeders, it is already well established that they can be weaned onto artificial diets, and thereafter successfully reared on them.

In a first trial, newly-hatched dover sole larvae were fed on the artificial diet None of the larvae survived to metamorphosis, but from regular inspection of the larvae, it was observed that a significant proportion were taking the diet, and since in many cases the gut could be seen to contain several granules, they were doing this consistently. Thus it was at least dear that the physical form of the diet was acceptable. Eventual death was most probably due to nutritional deficiency in the diet, and perhaps inadequate environment hygiene.

In a second trial, 0.1% of the larvae actually survived to metamorphosis. Although this does not at first sight compare favourably with the survival rates that can be obtained using live diets (80% or more using Artemza under the same environmental conditions), a survival rate of even 0.1% is highly significant, because this is to our knowledge one of the few occasions when dover sole larvae have been reared from hatching through to metamorphosis entirely on an artificial diet. Developments in the nutritional composition of artificial diets, and perhaps in environmental rearing systems, should increase the survival rate considerably.

Example 2.

The process of Example 1 was repeated, with the exception that instead of blending the edible oils into the substrate in the powder mixer, they were sprayed onto the tumbling bed prior to the application of the aqueous gelatin solution. This eased considerably the problem of premature agglomeration of the substrate by the free oils mentioned in Example 1. The final dried product had a granule size distribution and behaviour in water virtually identical to those of the product of Example 1.

Example 3.

A substrate was prepared by firstly milling a fish meal of oil content 9% by weight in a Hosakawa "Victory" (Registered Trade Mark) mill such that 100% by weight passed through a 106 micron screen and 60% by weight passed through a 50 micron screen. The milled fish meal (68 parts by weight) was mixed with 13 parts skimmed milk powder and 10 parts vitamin/mineral mixture, as in Example 1, and 4.55 kg of the resulting substrate was loaded into a 50 cm diameter pan granulator et at an angle of 30 to the horizontal and rotable at about 20 rpm. The mean particle size of the substrate was estimated to be about 60 microns.

The tumbling bed of substrate was sprayed with 0.45 kg of edible oils via a Delavan-Watson WG 126 nozzle, and then the substrate was sprayed with 0.3 Iitres of an aqueous solution containing 5% by weight sodium alginate (Manucol KMF Registered Trade Markex Alginate Industries) at ambient temperature (about 20 C) via the same nozzle at a working pressure of 80 psi. When granulation was completed, the product was dried at 500 C to a water content of approximately 10% by weight.

The final product had the following sieve analysis: Granule size (microns) % by weight of product > 250 52.0 106-250 46.5 < 106 1.5 The process thus produced a 46.5% yield of granulated feed in a size range appropriate for fish larvae, with a 52% fraction suitable for fish in the post-larval stage. The larval fraction had good compositional uniformity and very acceptable behaviour in water.

WHAT WE CLAIM IS: 1. A process for the preparation of a feedstuff for minute aquatic animals which require their diet to include granules having a maximum dimension of less than 300 microns, in which process a bed of finely-divided essentially solid feedstuff ingredients, having a mean particle size of not greater than 150 microns, is tumbled in a pan granulator and the tumbling bed is granulated by spraying thereon an aqueous solution of a non-toxic polymeric material, the granulated product so formed is dried to a water content of less than 15% by weight, and the granulated product is physically classi

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

these larvae have only been successfully first fed in a captive environment using a living diet, usually the brine shrimp Artemis salina. Once the larvae have metamorphosed, i.e. assumed their characteristic fiat shape and become bottom rather than pelafic feeders, it is already well established that they can be weaned onto artificial diets, and thereafter successfully reared on them.

In a first trial, newly-hatched dover sole larvae were fed on the artificial diet None of the larvae survived to metamorphosis, but from regular inspection of the larvae, it was observed that a significant proportion were taking the diet, and since in many cases the gut could be seen to contain several granules, they were doing this consistently. Thus it was at least dear that the physical form of the diet was acceptable. Eventual death was most probably due to nutritional deficiency in the diet, and perhaps inadequate environment hygiene.

In a second trial, 0.1% of the larvae actually survived to metamorphosis. Although this does not at first sight compare favourably with the survival rates that can be obtained using live diets (80% or more using Artemza under the same environmental conditions), a survival rate of even 0.1% is highly significant, because this is to our knowledge one of the few occasions when dover sole larvae have been reared from hatching through to metamorphosis entirely on an artificial diet. Developments in the nutritional composition of artificial diets, and perhaps in environmental rearing systems, should increase the survival rate considerably.

Example 2.

The process of Example 1 was repeated, with the exception that instead of blending the edible oils into the substrate in the powder mixer, they were sprayed onto the tumbling bed prior to the application of the aqueous gelatin solution. This eased considerably the problem of premature agglomeration of the substrate by the free oils mentioned in Example 1. The final dried product had a granule size distribution and behaviour in water virtually identical to those of the product of Example 1.

Example 3.

A substrate was prepared by firstly milling a fish meal of oil content 9% by weight in a Hosakawa "Victory" (Registered Trade Mark) mill such that 100% by weight passed through a 106 micron screen and 60% by weight passed through a 50 micron screen. The milled fish meal (68 parts by weight) was mixed with 13 parts skimmed milk powder and 10 parts vitamin/mineral mixture, as in Example 1, and 4.55 kg of the resulting substrate was loaded into a 50 cm diameter pan granulator et at an angle of 30 to the horizontal and rotable at about 20 rpm. The mean particle size of the substrate was estimated to be about 60 microns.

The tumbling bed of substrate was sprayed with 0.45 kg of edible oils via a Delavan-Watson WG 126 nozzle, and then the substrate was sprayed with 0.3 Iitres of an aqueous solution containing 5% by weight sodium alginate (Manucol KMF Registered Trade Markex Alginate Industries) at ambient temperature (about 20 C) via the same nozzle at a working pressure of 80 psi. When granulation was completed, the product was dried at 500 C to a water content of approximately 10% by weight.

The final product had the following sieve analysis: Granule size (microns) % by weight of product > 250 52.0

106-250 46.5 < 106 1.5 The process thus produced a 46.5% yield of granulated feed in a size range appropriate for fish larvae, with a 52% fraction suitable for fish in the post-larval stage. The larval fraction had good compositional uniformity and very acceptable behaviour in water.

WHAT WE CLAIM IS: 1. A process for the preparation of a feedstuff for minute aquatic animals which require their diet to include granules having a maximum dimension of less than 300 microns, in which process a bed of finely-divided essentially solid feedstuff ingredients, having a mean particle size of not greater than 150 microns, is tumbled in a pan granulator and the tumbling bed is granulated by spraying thereon an aqueous solution of a non-toxic polymeric material, the granulated product so formed is dried to a water content of less than 15% by weight, and the granulated product is physically classi

fied to ensure that it contains more than 10% by weight of granules having a maximum dimension of less than 300 microns.
2. A process according to Claim 1, wherein the ingredients of the tumbling bed have a mean particle size of not greater than 100 microns.
3. A process according to Claim 2, wherein the ingredients of the tumbling bed have a mean particle size of not greater than 50 microns.
4. A process according to any one of Claims 1 to 3, wherein the quantity of solu tion sprayed onto the tumbling bed is from 5 to 20 0/0 by weight.
5. A process according to any one of Claims 1 to 4, wherein the feedstuff contains oil and the oil is sprayed onto the tumbling bed before the aqueous solution is applied thereto.
6. A process according to any one of Claims 1 to 5, wherein the polymeric material is an edible gum of animal or vegetable origin.
7. A process according to Claim 6, wherein the polymeric material is a gelatin.
8. A process according to Claim 7, wherein the aqueous solution sprayed onto the tumbling bed contains from 2 to 15% by weight of gelatin.
9. A process according to Claim 6, wherein the polymeric material is an alginate.
10. A process according to Claim 9, wherein the aqueous solution sprayed onto the tumbling bed contains from 0.1 to 1.5% by weight of alginate.
11. A process according to any one of Claims 1 to 5, wherein the polymeric material is casein.
12. A process according to Claim 11, wherein the aqueous solution sprayed onto the tumbling bed contains from 2 to 15% by weight of casein.
13. A process according to any one of Claims 1 to 5, wherein the polymeric material is a starch, a degraded starch or a substituted cellulose.
14. A process according to Claim 13, wherein the polymeric material is a sodium carboxymethyl cellulose.
15. A process according to Claim 14, wherein the aqueous solution sprayed onto the tumbling bed contains from 0.1 to 5% by weight of sodium carboxymethyl cellulose.
16. A process according to any one of Claims 1 to 5, wherein the polymeric material is a water-soluble synthetic polymer.
17. A process according to Claim 16, wherein the polymeric material is a polyacrylamide.
18. A process according to Claim 17, wherein the aqueous solution sprayed onto the tumbling bed contains from 30 to 200 ppm of polyacrylamide.
19. A process according to any one of Claims 1 to 18, wherein the granulated product is dried to a water content of not more than 12% by weight
20. A process according to Claim 1, substantially as hereinbefore described with reference to Example 1.
21. A process according to Claim 1, substantially as hereinbefore described with reference to Example 2 or Example 3.
22. A granulated feedstuff prepared by a process according to any one of the preceding claims.
23. A granulated feedstuff prepared by a process according to any one of claims 1 to 19, and wherein more than 10% by weight of the granules have a maximum dimension of less than 250 microns.
24. A granulated feedstuff according to Claim 23, wherein at least 40% by weight of the granules have a maximum dimension of less than 250 microns but not less than 45 microns.
25. A granulated feedstuff according to Claim 23, wherein at least 80% by weight of the granules have a maximum dimension of less than 250 microns but not less than 45 microns.