September | October 2010

Feature title: Technical design and equipment: Key to improving feed quality and nutrition

The International magazine for the aquaculture feed industry

International Aquafeed is published five times a year by Perendale Publishers Ltd of the United Kingdom.All data is published in good faith, based on information received, and while every care is taken to prevent inaccuracies, the publishers accept no liability for any errors or omissions or for the consequences of action taken on the basis of information published. ©Copyright 2009 Perendale Publishers Ltd. All rights reserved. No part of this publication may be reproduced in any form or by any means without prior permission of the copyright owner. Printed by Perendale Publishers Ltd. ISSN: 1464-0058

Why do some feed facto-ries earn profits while others don’t? Why do feed of some factories

sell well? The reason behind is technical design and equipment selection.

Choosing skilled feed engineering con-structors and comprehensive solutions providers are also vital for the success of a company.

The factors affecting feed quality can be summed up in three aspects, namely:• The quality of raw material • The feed formula • The process technology

With the same level of raw material and formula, the quality of feed only depends on process technology and equipment performance.

As the digest system of chicken, pig, fish, shrimp and pet varies, feed of different size and degree of ripeness are demanded. It is one of the important methods for the modern feed companies to improve prod-uct quality by upgrading process technology.

Impact of grain size on feed nutritionGenerally, grain size should take con-

sideration of many factors like feeding method, process costs, capacity and growing characteristics of animals.

Its empirical value should be no more than 1/3 of the diameter of pellet.

Appropriate grain size can improve digestion rate of the nutritious element. Research has shown that if the even size of corn feed for sow is reduced from 1200um to 400um, its digestion rate could be raised by 14 percent, dry materi-als in manure could be reduced by 21 percent and the nitrogen would be lowered by 31 percent.

Over grind could lead to more consumption of energy, less capacity and destroy of nutrition of feed. The research data proves that VA of pellet

after repeated grind would decrease 40 percent.

The key point of grain size control technology is to grind each raw material to the best size suitable for digestion so as to ensure the batch feed can acquire best raising efficiency and economic profit. It is mandatory to study the best digestion size of each raw material for different animals as shown in Table 1.

Pulverization and micro-pulverization must be applied for aquatics feed.

Research has shown that carp feed ratio could raise 5-10 percent if the screen of grinder has been reduced from 1.5mm, 1.2mm to 1.0mm, 0.8mm, 0.6mm. As a result, grain size has a markable influence on variation of nutrition.

Grain with excessive small or big diam-eter could break into layers which would affect the digestion rate of feed nutrition. It is only by selecting proper technical design, professional company and equipment can good quality feed be made.

Impact of batch on feed nutrition

Formula is a major impact factor for feed nutrition and pellet quality. Formula with high content of grain like corn and soybean cannot produce high quality pellet feed due to the lack of natural bond.

Addition of highly cohesive wheat can improve pellet quality.

It is necessary to combine each element in the formula and keep fat to lowest limit. In case of large proportion of adding materials, the condition process should be

Technical design and equipment

Key to improving feed quality and nutritionby Shao Jianxin, Engineer, ZCME, China

Table 1: International best grinding particle size

Animal Raise stage

Best size recommended

(µm)

Pork

Ablactation 0~14d 300

Ablactation 14~35d 400

Grice ≤500�Corn�

Fattening pig 500~600�Corn�

Sow 500~600�Corn�

Growing pig 15~30kg 323(batch)

Dorking 700~900�Corn�

900

Beef cattle 1~1.5cm�straw�corn stalk�

2~7cm�corn stock�hay�

Fish ≤0.5mm�batch�

Shrimp 150~175

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F: Equipment

IAF10-05.indd 32 07/09/2010 14:56

adjusted or the materials should be added after pelleting.

As the core process of feed production, batching accuracy has a direct impact on feed composition and nutrition absorption of the animals. As a result, the feed nutrition can be balanced only with appropriate batching system.

The batching process has a important effect on batching accuracy and composi-tion. The major technical improvements lie in following aspects:

1: The batching scale must be checked regularly so as to ensure measure-ment accuracy of batching equipment

2: The formula should be right and the raw materials can be replaced

3: The materials should be fed at proper speed

4: The control system should be correct5: The batching equipment must be

operated in correct way6: The batching equipment should

be clean so as to avoid cross contamination

7: The batching process especially the use of medicine should be carefully recorded

No-error computer control technology is adopted to manipulate batching accuracy.

Micro additives can be premixed and batched and high accurate batching system can be adopted.

Impact of mixing conformity on nutrition

Conformity is vital for feed quality as it will determine whether the animal can get full nutrition from the feed. The air balance between mixing bin and mixer also has an impact on nutrition.

Too big finish product bins and pellet bins and too long transportation lines will destroy conformity of feed and reduce the conversion rate of the animal.

It is critical to choose the right mixer, mixing period and feeding method in order to ensure conformity and nutrition. The control of mixing conformity covers mixing feed, concentrated feed, additives, premix feed and liquid feed.

The technical improvements in batching process have the following aspects:

1: Proper mixer must be selected to ensure conformity

2: The materials should be added in cor-rect order with big materials added at first and small ones added later. All materials should be added in proper amount and order especially for pro-

duction of premix feed3: In case of change of for-

mula, the mixer should be thoroughly cleaned to avoid cross contamination

4: Premix should be sepa-rated from major mixing process in order to pre-vent cross contamination

5: The transportation distance and height of materials after batching should be as short as possible and no conveying equipment like pneumatic device should be adopted as it would cause separation of materials

Impact of pelleting on feed nutrition1. Pellet quality control: pellet

quality is the precondition of feed nutri-tion which must be strictly manipulated. The conditioning quality is the primary control point of pellet quality which includes temperature, time, water and ‘pasting degree’ of starch. A second-ary control point covers powder rate, cooling tempera-ture, mois-ture, blade-even degree and water durability of the feed. To meet the above require-ments man-ufacturers need proper steam supply and control systems, conditioning, pelleting, cooling and screening equipment with all control parameters scientifically adjusted.

The steam fed into con-ditioning units

must be unsaturated steam, free from con-densed water so as to ensure enough ‘pasting’ of starch and prevent machine blockage due to too much moisture. The steam must go through a water trap and a pressure reducing valve before entering the conditioner.

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ing of feed with vitamins is as following: temperature ≥90°C, moisture≥15%, time ≥60 seconds. As a result, it is necessary to choose formulation with sound thermal stability. A good pellet conditioner, correct air admission and mixing methods are also the vital factors for pelleting process.3. Feed enzymes: pellet proc-ess also affects feed enzyme and other microbials. Enzyme and microbial are bio-logical products, the activity of which are usually damaged under the comprehensive function of high temperature, humidity and pressure. It is reported that the activity of phytase drops by 87.5 percent at temperatures of over 80�. So the utilisation rate of N.P. will be affected. The microbe addi-

tives in the feed is especially reactive to high temperature so that its activity will be lost completely if the pellet temperature exceeds 85�. It is better to coat enzyme after pelleting or to use enzymes with better thermal stability.

4. Impact on anti-nutrition factors: part of anti-nutrition factors and harmful substances will be killed during the conditioning of pellet. Anoxia sterilisation before pelleting can kill various bacteria effectively and improve feed quality. It has been a key research subject for profes-sional technicians.

Animals have different reactions to the same anti-nutrition factors as its spe-cies and age vary. The anti-nutrition factors can be divided into positive inhibitors for carbohydrate, miner-als and prolease, etc. The pelleting

process adopts conditioning, high temperature extrusion methods to weaken the anti-nutrition factors as listed in Table 2 to maximum limit. 5. Impact of pellet on starch and protein: the starch would become ‘pasted’ and protein would be denaturated after conditioning so that the ani-mal can digest and aborb the starch and protein better. However, it is the technical issue of a professional com-pany to determine the raw

High temperature conditioner with short time (60-160 seconds) can kill bacteria.

Many conditioners of this type have been developed in several countries. The durabil-ity of feed at high temperature should also be considered during conditioning. 1: Materials with bad durability under

high temperature and poor ‘strength’ should avoid conditioning at high temperature. Instead, they should be coated later so as to ensure pellet quality.

2. The impact on vitamins: it is vulner-able to increase conditioning time and raise temperature as the vitamins with poor thermal stability would be easily lost during the pelleting process. Vitamins like A, E, C, thiamine hydro-chloride, etc will be killed rapidly as the temperature and conditioning time is raised.

The critical condition for condition-

Meanwhile, the flow rate of steam must be matched to the feeding rate. As a result, steam with proper characteristics is a precondition of pellet quality.

Technical improvements of steam pres-sure and flow rate covers following aspects to ensure high quality of feed:

1: Control the conditioning of meals, including the adding of steam and oil, and check the quality of steam and keep a good record of it

2: Control the product from the pellet mill and keep record of it

3: Control the cooling time, moisture and temperature of feed in accord-ance with the room temperature and moisture

4: Control the fat coated on the surface of feed

5: Check the hardness of pelleted feed and keep good records

Conditioning process is vital for pellet quality. The mixed materials with high content of grain usually stay for at least 40-60 seconds in the conditioner.

Meanwhile, the temperature inside the conditioner should be kept between 85-98� to improve ‘pasting’ of starch. Materials with high fibers must stay for shorter time in the conditioner. In case of addition of liquids like molasses, the materials should stay longer in conditioner (maximum 30 minutes) so that it would absorb molasses fully.

Table 2: Anti-nutritional factors of common raw materials of feed

Anti-nutritional factors Distribution Inhibit function

Protease inhibitor

Pea seed, beet broomcorn

Restrain activity of trypsin and pepsin, facilitate secrete of pancreas

GlucosideRapeseed, cabbage,

Kale, etc Prohibit growth, increase cardiolipin and reduce appetite

Lectin Pea seedImpair intestinal wall, lose more endogenous protein, inhibit

growth

TanninPea seed and cake,

etc Weaken absorption of protein, carbohydrates

Gossypol Cottonseed and cakeinjures gastric mucous membrane, destroy metabolization of

protein and iron

Phytic acid Pea seedInterfere biological effectiveness of mineral elements, form protein

complex

Saponine Soybean Destroy absorption of nutrition, reduce appetite

Lignin Pasture Destroy absorption of nutrition, reduce appetite

Alkaloid Pasture Reduce appetite, inhibit growth

NSP Grain feedFacilitate pasting of materials inside enteron, weaken absorption

of nutrition

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of anti-nutrition factory and keep vita-mins; enzymes preparation cannot only erase toxic effect of feed but also provide a health function.

Getting rid of anti-nutrition factors in raw materials has become vital in selec-tion of process technology and equipment. Feed quality and nutrition can be only be guaranteed using professional technol-ogy and equipment. With the development of nutrition, technicians of professional company can work out better methods to eliminate anti-nutrition factors and make more contribution in improving feed quality and nutrition.

of security, sanitation and nutrition of feed, it is necessary to equip residue-free conveyor and bins, apply scientific technology of cleaning and sequencing. Heat treatment technology should be applied which includes cooking at high temperature, extrusion, high-pressure treatment and ultraviolet irradiation, etc. With the comprehensive application of the above technology, the finish pellet feed can obtain satisfactory quality and nutrition.

Impact of technical processThe anti-nutrition factors in feed can

cause disease of pigs and pets and retard the growth process. As they are closely related with process technology, nutrition-ists have developed many methods to elimi-nate anti-nutrition factors.

However, the nutrition elements in feed would lose at the same time. Extrusion and expansion at high tempera-ture can improve feed quality and limit lost of nutrition; anoxia sterilisation could kill bacteria effectively and keep vitamins; fermentation could eliminate toxic effect

material of specific size for specific animals. Protein denaturation has little influence on amino acid but improves its absorption rate greatly so that protein can be highly utilised.

6. The impact of post-cooking: after conditioning, the ‘paste’ degree and water durability of pellet should be improved, however, some thermal alert vitamins are destroyed. As a result, it is better to use formulations with sound thermal stability or apply the improved coating technology so as to preserve nutrition values of the feed as much as possible; which is mostly used in the production of aquatics feed or special aquatics feed for shrimp for example.

7. Impact of storage and transportation: cross contamination usually takes place during storage and transporta-tion. Residue in transportation vehi-cles, bins, buffer hoppers and process equipment could cause cross contami-nation. Harmful microbe and pests are also source of cross contamination.

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34 | InternatIonal AquAFeed | September-october 2010 September-october 2010 | InternatIonal AquAFeed | 35

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binders or natural binders on the digest-ibility of the feeds growth of shrimp

Material and MethodsDiets - Three different diets were for-

mulated (see table). Feeds were pelleted on a 2mm die.

ResultsL e a c h i n g

rate and water uptake - Analysis for leaching rates and water uptake were done at the labora-tory of CreveTec. Leaching was done during one hour in fresh water.

As could be expected from previous results, the inclusion of ureumformal-dehyde reduces the water uptake that in turn reduces the leaching rate. The values for the three diets are within standards.

DigestibilityThe three samples of feed were analysed

for in vitro digestibility with the pH stat method, as described by Lemos et al (2009). DH values were used to predict protein digestibility by separate models relating ingredients or diet DH to in vivo digest-

ibility as verifiable in Lemos et al. (2009). Feed samples with PPD (Predicted Protein Digestibility) from 90.7 to 92.0% may be considered of high to very high protein digestibility diets.

Growth trialExperimental system - Shrimp were put

in 12 nets of 150 liters each. The nets were submerged in a bigger tank, which is con-nected to a biofloc reactor. Water quality is maintained through bioflocs and is the same in all nets. There were four replicates for each diet.

ShrimpEach net was stocked with 25 shrimp

(Litopenaeus vannamei) of 12-13g each. They were acclimatised in the nets during

Table 1: Composition of test diets

Ingredient Diet WG Diet PBP Diet UF

Corn gluten 11 11 12,5

Fish meal 20 20 20

Wheat flour 31 31 31

Pro-Bind Plus - 2 -

Wheat gluten 2 - -

Urea-formaldehyde - - 0,5

Other * 7,5 7,5 7,5

Crude protein 37,74 38,01 38,05

Crude lipid 8,61 8,66 8,63

Crude fibers 2,92 2,91 2,94

Ash content 6,44 6,48 6,47

* Canola, Soybean meal, Fish oil, Soybean lecithin, premix

Table 2: Leaching rate and water uptake of test diets

Sample Diet WG Diet PBP Diet UF

Water uptake 107,63% 105,13% 89,89%

Leaching rate 7,75% 8,29% 6,75%

10 | InternatIonal AquAFeed | September-october 2010 September-october 2010 | InternatIonal AquAFeed | 11

F: Binders

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Influence of natural and artificial binders

- in feeds for Litopenaeus vannamei on digestibility & growth

Ecobiol Aqua - the effective single strain probiotic

A general overview aquaculture in the EU

Abalone feed development in South Africa

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