Effects of dietary n-3 polyunsaturated fatty acids and ... - FINS

1 st WorkshopXIII International Feed Technology Symposiummoisture feed processing conditions are questionable. Although a number ofinvestigations from the feed industry suggest that binding capacity of starch containingfeed ingredients increases with heat treatment and starch gelatinisation [4], the role ofstarch for physical pellet quality is not clearly defined. Results by Svihus et al. [9] evenindicate that starch may not be a major contributor to the pellet quality, and Gilpin et al.[3] found a negative correlation between degree of gelatinisation of starch and pelletdurability.MATERIAL AND METHODSAll diets were processed at Centre for Feed Technology, Norwegian University of LifeSciences (Ås, Norway).In present experiment a diet composed of equal amounts of rapeseeds, fishmeal and oathulls was made. The ingredients were selected so that the starch content was minimized(Table 1), and so that physical quality would be poor after pelleting, thus assuring thateffects of starch on physical quality could be revealed. The oat hulls were added asunground oat hulls from the dehulling process, whereas rapeseeds were ground in ahammer mill (Münch-Edelstahl, Wuppertal, Germany licensed by Bliss, USA, 18 kW,3000 RPM) fitted with a 3 mm sieve before processing. One part of the diet was dilutedwith 200 g/kg of a wheat starch (Raisio Grain Starch Ltd, Raisio, Finland). Each of thesetwo diets was thereafter divided into 6 batches which were either cold-pelleted or steampelleted.In addition, one part of the diet was diluted with 200 g/kg of gelatinised wheatstarch prior to division into three batches and steam-pelleting. Batch size was 100 kg anda sample was collected after temperature had become stable. The gelatinised wheatstarch was produced by long-term conditioning, and was measured to have an extent ofgelatinisation of 796 g/kg.Cold-pelleting was achieved by by-passing the conditioner and pressing mixedingredient mash through the pellet press die (Pellet press, Munch Wuppertal - Germany,5t/h, 2x17.5 kW, RMP 350.100) at a production rate of 700 kg/h. Steam-pelleting wasperformed by heating the material with steam at 75˚C for approximately 20 to 30seconds in a pellet press conditioner prior to pelleting. Dimensions of the pellet die were5 mm diameter and 60 mm thickness. The large pellet diameter was chosen to assure alow pellet durability of the diets without starch. In order to achieve similar moisturecontent among processing methods 30 to 40 g/kg of water was added prior to coldpelletingusing a nozzle Teejet 4003.A sample was collected at the exit of the pellet press in an insulated box fitted with athermometer (Electronic Thermometer, TESTO 110, GM 295 14 770, Germany) tomeasure post-pelleting temperature.After processing, all pelleted diets were cooled in a Miltenz counter-flow cooler(Miltenz, Auckland, New Zealand, 2000 kg/h capacity) for ten minutes. Moisture contentafter cooling was 130 g/kg, with maximum 10 g/kg variation between diets.Fines percentage in pelleted diets were measured by sieving approximately 100 g ofcarefully homogenized pelleted feed through a 4.0 mm sieve while vortexing (amplitude1.5 mm) on a Retsch AS 200 sifter (F. Kurt Retsch GmbH & Co., Haan, Germany) forone minute. Durability of the pellets was measured using a Holmen pellet tester (HolmenChemical Ltd., Borregaard Group, Norsolk, UK) and a Ligno pellet tester (Borregaard46