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The objective of the present study was to investigate whether mixing ratio of maize and soybean meal (SBM) affects the breaking behaviour during hammer-milling in terms of the nutrient properties and in vitro digestibility of fractionated particles. Mixtures of maize and SBM with different proportions (% Maize:SBM; 0:100, 25:75, 50:50, 75:25, 100:0) were hammer milled using a 2-mm screen. The obtained powder was sieved into seven fractions with size ranges from 0.149 to 1.190 mm. Results show that energy consumption of grinding mixtures increased from 3.8 to 48.4 kJ/kg with the maize proportion increasing from zero to 100%. Mixing proportion of maize and SBM showed significant effects on nutrient content of fractionated material. For hammer milled material <595 µm, the in vitro digestibility of crude protein (CP) and organic matter (OM) of fractionated material decreased with increasing particle size. Additionally grinding fractionated particles ≥595 µm over a 1-mm sized screen before in vitro digestion analysis increased the digestibility of OM and CP. Equivalent particle size (EPS) and geometric standard deviation (GSD) of hammer milled maize and SBM and their mixtures correlated better than geometric mean diameter (GMD) to OM and CP in vitro digestibility in a linear regression model. In summary, the mixing ratio of maize and SBM had a significant effect on the breaking behaviour of ingredients and in vitro digestibility of CP and OM of the isolated fractions. Mixing ingredients before grinding is suggested in terms of saving energy consumption. The GSD/EPS of ground material should be considered while studying the effects of particle size distribution on the in vitro digestibility of nutrients.

Grinding is an important feed processing technology, determining physical and nutritional characteristics of ground materials, which affects nutrient digestion in animals and their growth performance. This study aimed to clarify if differences in moisture content (MC) lead to differences in nutrient composition over various particle size fractions after grinding that have potential to affect feed manufacturing characteristics or animal performance. Maize and soybean meal (SBM) with targeted MC of 120, 140 and 160 g/kg (adding no (0), 30 and 60 g/kg of tap water, respectively) were hammer-milled and the physical and chemical characteristics as well as in vitro apparent ileal digestibility (AID) of particle size fractions were determined. The mill was fitted with a 6-mm (maize) or 2-mm (SBM) sized screen, with milled material subsequently separated by dry sieving (size ranging from < 0.075 to > 3.36 mm) and each fraction was analyzed for its nutrient composition, morphology characteristics and in vitro AID of organic matter (OM) and crude protein (CP). For the latter assay, specific particle size fractions were additionally ground using a laboratory mill (1 mm screen). Geometric mean particle size diameter and energy consumption increased with increasing MC (P < 0.05). Chemical composition, physical characteristics and in vitro AID of particle size fractions were significantly different (P < 0.001). Moisture addition had no significant effect on nutritional and physical parameters except for solidity in maize, ash content, projected area, circularity, and solidity in SBM. Physical characteristics of particles, especially particle size affected in vitro AID of OM and CP most (P < 0.05). Additional grinding of samples before determination of in vitro AID increased the OM digestibility up to 0.684 in maize (P < 0.001). Additional grinding of particles larger than 0.595 mm increased in vitro AID of OM and CP (P < 0.05). In summary, increasing MC has limited effect on the

Particle size plays an important role in the digestibility of nutrients by animals. Methodologies developed to simulate the digestive system to determine digestibility values require the grinding of samples to pass a specific sieve size (e.g. 1 mm) before in vitro digestion. The objective of this study was to evaluate if particle size affects in vitro (ileal) digestibility values of organic matter (OM) and crude protein (CP) in maize and soybean meal (SBM). Both ingredients were ground in a laboratory mill over four screens (1.50, 1.00, 0.75 and 0.50 mm) with trapezoidal holes in a sequential manner from large to fine. Particle size distribution, nutrient content and in vitro digestibility were determined of the various samples. With decreasing screen size, geometric mean diameter of particles significantly decreased from 351.4 to 203.2 µm for maize, and from 239.1 to 99.1 µm for SBM. Ash, CP and starch content were not affected whereas the neutral detergent fibre in maize and dry matter content in SBM differed after grinding with various sized screens (P < 0.05). The in vitro digestibility of OM and CP of maize and CP of SBM ground over the four different screens did not differ (P > 0.185). The OM in vitro digestibility differed (P < 0.05) with values for SBM ground over the 1.50 mm screen being lower (P < 0.05) than the smaller screen sizes: 0.814 (1.50 mm) vs 0.833 (1.00 mm), 0.829 (0.75 mm) and 0.834 (0.50 mm), respectively. Based on the current work and literature data, particles ≥ 595 µm of comminuted maize and SBM affect OM and CP in vitro digestibility. Analysis of three feeds and 10 feed ingredients ground over a 1.0 mm sieve showed that the fraction ≥ 595 µm can make up to 32.1% of the mass. It is recommended that before in vitro digestibility determination, particle size distribution is assessed, especially the mass fraction of particles ≥ 595 µm and further grinding is conducted to ensure that particles are < 595 µm for maize and SBM. The cut off size wh

Feed processing involves the use of various technologies to transform feed ingredients into valuable feeds enabling the production of animal-sourced foods (e.g. meat, eggs, milk). Hammer-milling, a standard technology used in the feed industry, is a critical process affecting feed efficiency and animal production. After grinding, the particle size of ingredients is reduced, the physical characteristics of particles and nutrient distribution are changed, which can affect the digestibility and kinetics of nutrient digestion.The research described in this thesis provides hitherto unknown insights into the breakage of maize and soybean meal as a result of hammer-milling via physical and chemical characteristics as well as in vitro digestibility of nutrients of size-fractionated particles. Moisture content and mixture ratio effects of feed ingredients on the breaking behaviour were also investigated enabling the development of novel grinding strategies to produce feeds with higher nutrient digestibility. This thesis provides important data on the importance of sample preparation before in vitro digestion analysis to improve the prediction and repeatability of nutrient digestibility estimates.

The mean particle size of ground grains influences both pig growth performance and gastric health although this effect is not consistent and the underlying reasons are not fully understood. The inhomogeneous nutrient content distribution in particles of different sizes and the characteristics of particles may be reasons for inconsistent findings. The objective of the present study was to determine the nutrient content and physical characteristics of individual size fractions of hammer-milled maize and soybean meal (SBM), and to relate it to in vitro digestibility. Maize and SBM were hammer-milled over a 6- and 2-mm size screen, respectively, and were sieved into seven fractions. Particle characteristics of the hammer-milled material were determined by dry sieving, wet sieving and image analysis methods; the nutrient composition including dry matter, ash, crude fibre (CF), crude fat (CFat), crude protein (CP), starch and in vitro digestibility of organic matter (OM), CP (SBM) and starch (maize) were measured and nitrogen-free-extract was calculated. The results show that the nutrient composition differed among fractions of ground maize and SBM (P < 0.001). A large difference in starch levels (754.2 vs 578.9 g/kg) of maize was observed between the various sieve size fractions whereas the CP content of SBM increased with larger sieve sizes. The in vitro digestibility of OM and CP was different (P < 0.001) among the various particle size fractions for both ingredients. However, the in vitro digestibility of starch did not differ between each size fraction in maize (P = 0.060). The regression models relating the nutrient composition and in vitro digestibility show that the digestibility of OM was positively related to the starch level (P < 0.001). As for SBM, CF (negatively) and CFat (positively) were correlated with OM digestibility (P < 0.001); ash and CF had a negative effect on the digestibility of CP, though CFat had a positive relation with the CP digestibility (P

Particle size of diets or ingredients plays an important role in pig growth and gut health. The way the size of particles is measured and expressed, however, is limited in explaining pig growth performance differences. This review explores new possibilities to determine, express and predict particle size. Different grinding methods, including the use of roller mills, hammer mills, multicracker and multi-stage grinding were reviewed. Roller milling tends to produce a more uniform particle size distribution (PSD) and consumes less energy, whilst hammer mills have a greater grinding capacity and a higher reduction ratio compared to roller mill. The multicracker system, a more recently developed technology, can be considered cost-effective and ensures grinding capacity. Since the effects of different grinding methods vary, multi-stage grinding, combining different grinding methods, might be a solution to obtain a defined PSD. Particle size determination techniques, including dry/wet sieving, laser diffraction, microscopy, and static/dynamic image analysis are described and compared. It is concluded that more characteristics of particles (e.g. shape, volume or surface area) should be investigated. Besides geometric mean diameter (GMD), particle size can also be expressed with parameters such as D50, D4,3 and span of PSD. Equivalent particle size (EPS) is introduced as a mean of describing the size of particles related to a functional trait of the particles. A meta-analysis was performed by collecting particle size and pig performance data from scientific studies examining the effect of recalculated EPS on pig performance (feed conversion ratio, FCR). Regression/linear modelling shows that recalculated EPS was not better than GMD in explaining pig performance differences due to the high variation among studies. Different expressions of PSD may result in different conclusions. An introduction of describing the breaking behavior of diet ingredients via mathematical models i

Diet preferences of broiler chickens were studied during 3 different choice-fed periods (P1, P2, P3). In P1 (1 to 7 days), chickens received a crumble starter diet with 250g/kg ground wheat (GW) in two separate feed troughs with dry and wet feed (1:1 feed to water). During P2 (8 to 21 days), chickens received diets in four separate feed troughs with whole wheat (WW) and GW in a 4 mm pelleted diet, fed dry and wet. In P3 (22 to 34 days), chickens received WW and GW dry pellets of 4 and 6 mm diameter in 4 separate feed troughs. Ingredient compositions of all diets from day 8 to 34 were similar (350g/kg wheat). Consumption from each feed trough was measured daily over a 6h-period. In P1, a strong preference for wet feed was found of 90.7% of total air-dry feed intake (P<0.001). In P2, preferences over the 4 diets were WW wet (62.6%), GW wet (33.7%), WW dry (2.6%) and GW dry (1.1%). Separate statistical analyses were done for the 6 slowest growing pens (SGP) (64g/d) and the 6 fastest growing pens (FGP) (70g/d). A positive correlation between average daily gain (ADG) and WW wet consumption was found for SGP (r=0.88, P=0.022) and a negative correlation for FGP (r=-0.83, P=0.042). Moreover, the ADG of FGP correlated positively with dry WW intake (r=0.81, P=0.050). In P3, preferences over the 4 diets were WW 6mm (33.4%), WW 4mm (33.2%), GW 4mm (24.3%) and GW 6mm (9.1%). Only FGP showed a preference for 4mm pellets (60.2% P= 0.005). The ADG of FGP were negatively correlated with WW intake in general (r=-0.83, P=0.039); no significant correlations were found for SGP. It is clear that chickens strongly prefer wet over dry diets and a high intake of a wet diet in combination with WW seems to benefit the slowest growing chickens. WW is preferred over GW, however a somewhat higher GW versus WW intake seems to benefit the faster growing chickens. The preference for 4 over 6 mm pellets seems to depend on growth rate and diet structure.

The effects of different temperature and time conditions during retorting of canned cat food on physicochemical characteristics and palatability were examined. For this purpose, lacquer cans containing an unprocessed loaf-type commercial cat food were heated in a pressurised retorting system at three specified temperature–time profiles (113°C/232 min, 120°C/103 min and 127°C/60 min) to equal a similar lethality (F 0 value = 30). Physicochemical properties (viscosity, texture, particle size, pH) were determined, and a 10 d three-bowl palatability test was performed with ten European shorthair cats. Retorting at 113°C/232 min resulted in differences in all the physical parameters examined ( particle size). Significant pH differences were observed (6·53, 6·63 and 6·66 for T113/232, 120 and 127°C, respectively). Preference ratios were 0·38, 0·31 and 0·31 for T113/232, 120 and 127°C, respectively (P = 0·067). It can be concluded that different retorting temperature–time profiles with equal F 0 value significantly affect physical characteristics and tended to affect palatability of moist cat food.