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KOPCEKOVA, J., CERESŇAKOVA, Z., FĽAK, P., MLYNEKOVA, Z.: Eff ect of mechanical processing of ce reals on rumen starch degradability. Acta univ. agric. et silvic. Mendel. Brun., 2010, LVIII, No. 2, pp. 139–146 Although starch in cereal grain is almost completely digested in the whole digestive tract, the rate and extent of ruminal degradation and fermentation vary widely with grain source and cereal processing. The objective of this study was to determine the eff ect of particle size (≤ 1.4, 1.5–2.5, 2.6–3.0 and > 3.0 mm) of mechanically processed wheat, barley and maize on ruminal degradation of starch. Standardized in sacco method was used to determine the degradation of starch in mechanically processed grains with incubation times of 0, 3, 6, 9, 16, 24, and 48 hours for maize, respectivelly. Signifi cant differences of starch eff ective degradability (EDg) were determined among experimental feeds as well as dependence on particle size of feeds. Among cereals, wheat had the highest eff ective starch de gra dabi li ty (83.0–95.2%), the lowest was found for maize (52.1–76.1%). Eff ective degradability of starch was the highest for the smallest particles (≤ 1.4 mm), 95.2 for wheat, 91.2 for barley and 76.1% for maize. The eff ective degradability of starch was decreased with enlarging of particle size of used grains. These results indicate that optimal degree is coarsely grinding, because larger particles increased passage of starch to the duodenum. cereals, grain processing, starch, in sacco degradability Starch is a primary nutrient of those ruminant diets used to promote high levels of production. Optimal starch utilization is fundamental to improve effi ciency of animal production. The main sources of starch in the diets are the cereals, commonly barley, corn and sorghum (Theurer, 1986). Degradation variability of saccharides infl uences the fermentation processes in the rumen, passage of nutrients into the small intestine and nutrients digestibility (Pajtas and Simko, 2003; Simko et al., 2008). Although starch in cereal grains is almost completely digested in the digestive tract, the rate and extent of ruminal fermentation varies widely with grain source and processing of cereals (Owens et al., 1986; Huntington, 1997). For most kinds of grain, except corn and sorghum, at least 90% of starch is fermented in the rumen. With corn, up to 30% or more could escape ruminal fermentation; most of starch escaping fermentation would be digested in the small intestine or fermented in the large intestine. Whole kernels with an intact pericarp are very resistant to bacterial colonization and penetration of starch granules. The fi rst goal of mechanical processing is to break the outer coat of the grain and increase microbial access to starch, and consequently to increase rumen and total tract starch digestion (Remond et al., 2004). Partical size reduction increases the surface available for adhering of microbial population and provides more substrate for amylase activity (Nocek and Tamminga, 1991; Off ner et al., 2003). The objective of the present study was to evaluate the eff ect of particle size of cereal grains on the ruminal starch degradation. MATERIALS AND METHODS Standardized in sacco method (Harazim and Pavelek, 1999) was used to determine the degradation of starch in mechanically processed grains of wheat, barley and maize with incubation times of 0, 3, 6, 9, 16, 24 hours, and 48 hours for maize, respectivelly. The parameters of starch degradation and eff ec140 J. Kopcekova, Z. Ceresňakova, P. Fľak, Z. Mlynekova tive degradation were calculated using the Neway programme (Rowett Research Institute) based on the equations described by Orskov and McDonald (1979). An outfl ow rate 0.06 and 0.08.h−1 was used in the calculation of eff ective starch degradation. Chemical composition of feeds and residues a er incubations were determined by the Weende system analysis (STN, 1985). Starch was determined by the enzymatic method according to Salomonsson et al. (1984). Maize (DK 471), winter wheat (Brea) and spring barley (Jubilant) were used as experimental material. Feed samples were processed by grinding in grain hammer mill. The samples of ground feeds were separated in a set of sieves to obtaining particles of diff erent size (Table I). Experiments were performed with two dry cows of Black Spotted breed. The animals (an average liveweight 645 kg) were fi tted with a large rumen fi stula (O 10.5 cm). Daily ration consisted of lucerne hay (4 kg), maize silage (6 kg), concentrates (2 kg, wheat and barley in ratio 1:1) and mineral-vitamin additive. Roughage represented 75% out of total dry matter content in ration. Level of nutrition did not exceed 1.5 times of maintenance requirement. Animals were fed twice daily (at 6.00 and 18.00) with free access to drinking water. Basic statistical characteristics for individual studied factors (feed, treatment, incubation period) were calculated. Two and three way variance analyses were used for evaluation of the mentioned factors and their interactions. The signifi cant interactions of feed x treatment and feed x incubation times, were depicted graphically. The linear and quadratic functions for relationship among starch degradation and particle size or incubation times were calculated. Applied mathematical and statistical models were in statistical package Statistix 8.0 by Grofi k and Fľak (1990), and Microso Offi ce Excel 2007 computer program was used for graphical processing. RESULTS AND DISCUSSION Among individual species and varieties of grain feeds there are diff erences in their degradation, resulting from chemical composition and physical structure, which becomes evident in the extent and rate of their change in the rumen (Matthe, 2001). Lebzien and Engling (1995) referred that by wheat feeding, about 89% of starch is fermented in the rumen, by barley about 81% and only 69% maize. Ceresňakova et al. (2003) determined signifi cant diff erences in degradability of starch in various cereals fed to ruminants. The lowest degradability of starch was determined in maize grain and the highest one in wheat varieties. The highest disappearance of starch in wheat and barley was determined during the fi rst three hours of incubation, 43.8–93.5% for wheat and 45.3–93.3% Particle size of experimental feeds I: screen size of sieves (mm) particle size (mm) share of fraction a er grinding of 1 kg meal (%)

Effect of mechanical processing of cereals on rumen starch degradability