Kari Lundblad defended her PhD thesis on June 5th 2009

Ane Gro Siri Skjelfjord

Effect of diet conditioning on physical and nutritional quality of feed for pigs and chickens

The aim of the study was to investigate water adsorption in raw materials during conditioning with steam or water, and how steam conditioning with low and high temperature, expander conditioning and extruder processing affect physical and nutritional quality of pelleted feeds for nursery pigs and broiler chickens. Physical quality was measured as pellet durability index (PDI) using the tumbling box procedure, whereas nutritional quality was measured as average daily gain (ADG), average daily feed intake (ADFI), gain to feed (G:F) and nutrient digestibility. In total, four experiments were carried out.

Experiment one was carried out to study water adsorption in various raw materials in moist air (80°C) or rehydrated in water (20 and 80°C). Raw materials were protein rich (soybean meal and rapeseed cake) or starch rich (wheat, barley, dehulled oats, sugar beet pulp, maize and wheat bran), milled to fine (<0.5 mm) or coarse (>0.5 mm) particle size. Chemical composition of raw materials and physical state of water affected water adsorption. Greatest water adsorption was observed in starch rich raw materials milled to small particle size and rehydrated in water at 80°C. Protein rich raw materials adsorbed most water in moist air, whereas particle size and water temperature did not affect water uptake when rehydrated in water. Overall, raw materials rich in starch adsorbed most water, especially at 80°C water temperature, but fastest water adsorption was observed for the protein rich raw materials. The results suggest that a combination of steam and water should be used to optimize the effect of conditioning during the manufacture of pelleted animal feed.

The aim of experiment two was to investigate the effect of adding water into the mixer on physical quality of a barley-based and a maize-based diet for finishing pigs, without or with use of an expander. For the barley-based diet, treatments were 0, 1.5, 3, 6 and 12% water added into the mixer, whereas 0, 1.5 and 3% water was added into the mixer for the maize-based diet. The mixed mash was steam conditioned at 82°C prior to pelleting. Overall, the results showed that the barley-based diet had a greater PDI than the maize-based diet when no water was added into the mixer. The maize-based diet showed greater improvement in PDI (from 79 to 87%) when 0 to 3% water was added into the mixer compared to the barley-based diet that showed only a slight improvement in PDI (from 91 to 93%) when 0 to 12% water was added into the mixer. When no water was added into the mixer, use of expander on the maize-based diet improved PDI from 79 to 92%. When until 3% water was added into the mixer, expander conditioning improved PDI in the maize-based diet from 92 to 94%. Expanding the barley-based diet resulted in a slight improvement in PDI when no water was added into the mixer. When water was added into the mixer, expander conditioning improved PDI in the barley-based diet from 93 to 95%. The results suggest that the greatest effect of water addition into the mixer on PDI, without or with use of an expander, can be achieved on diets with initial low pellet quality, like the maize-based diet. Diets with an initial high pellet quality, like the barley-based diet, gives little room for further improvement in PDI.

The aim of the third experiment was to investigate the effect of steam conditioning at low and high temperatures, expander conditioning or extruder processing prior to pelleting a wheat-based diet formulated to 1.35% lysine for nursery pigs and broiler chickens. The treatments were: 1) unconditioned mash as control; 2) low-temperature steam conditioning (47°C for 20 sec) before pelleting; 3) high-temperature steam conditioning (90°C for 20 sec) before pelleting; 4) expander conditioning (77°C for approximately 20 sec in a pre-conditioner and 105°C for 20 sec in the expander barrel) before pelleting; and 5) extruder processing (92°C for 150 sec in a pre-conditioner and 120°C for approximately 50 sec in the extruder barrel). The effects of diet conditioning on ADG, ADFI, G:F and nutrient digestibility, were determined. In nursery pigs, hydro-thermal processing, and in particular extruder processing, improved G:F compared to the mash control. For the total experimental period (d 0 to 36), ADG did not differ among pigs fed the different treatments, whereas ADFI was higher for pigs fed the mash control compared to pigs fed the hydro-thermal processed diets. Starch digestibility was greater in pigs fed the extruded compared to the expanded diet. In broiler chickens, there was no advantage in extruding or expanding compared to steam conditioning prior to pelleting the diets. Average daily gain and ADFI were greater for broiler chickens fed the steam conditioned diets compared to those fed the expander conditioned and the extruder processed diets. Expander conditioning resulted in greater ADG and ADFI than extruder processing. Starch digestibility was greater in broiler chickens fed the hydro-thermal processed diets compared to those fed the mash control. The results suggests that hydro-thermal conditioning is beneficial for nursery pigs, but not for broiler chickens.

The aim of experiment four was to investigate apparent ileal digestibilities of dry matter (DM), crude protein (CP), amino acid (AA), starch, neutral detergent fibre (aNDF) and phosphorous (P), and standardized ileal digestibility of CP and AA in growing pigs fed the same diets as used in experiment three. Six growing pigs with a T-cannula in distal ileum were used in the experiment. Hydro-thermal processing significantly increased starch digestibility and decreased aNDF digestibility compared to the mash control. No significant effect of hydro-thermal processing was observed on digestibility of DM, CP or P. For total essential amino acids (EAA), apparent ileal digestibility and standardized ileal digestibility was improved by hydro-thermal processing, as were the coefficients for Arg, Ile, Lys, and Thr compared to the mash control. For Phe, standardized ileal digestibility was significantly improved whereas apparent ileal digestibility tended to be improved (P = 0.056) for the advanced (expander and extruder) compared to the conventional (steam pelleting at low and high temperatures) hydro-thermal processing. For Lys, apparent ileal digestibility and standardized ileal digestibility were significantly greater also for pigs fed the advanced compared to conventional hydro-thermal treatments. Digestibility of non-essential amino acids (NEAA) was not affected by any of the dietary treatments. The results suggest that hydro-thermal processing have a positive effect on digestibility of essential amino acids.

Keywords: conditioning, feed ingredients, pellet quality, rehydration, water adsorption, pellet durability, PDI, expander, water in mixer, pelleting, extruder, steam conditioning, feed processing, feed manufacturing, apparent digestibility coefficients, nursery pigs, broiler chickens, apparent ileal digestibility, standardised ileal digestibility, amino acids

Updated: 01.07.09
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