Extrusion of sorghum starch enhances ruminal and intestinal digestibility, rumen microbial yield and growth in lambs fed on high-concentrate diets

Abstract This study consisted of two experiments that investigated the effect of extrusion of sorghum starch on in situ ruminal and post-ruminal disappearance of dry matter (DM), starch and nitrogen (N) and the effects of substituting barley by the extruded sorghum on digestion characteristics, microbial N supply and growth in finishing lambs. Sorghum was extruded using the following four temperature and pressure combinations: T1 = 90 °C/17 bars, T2 = 115 °C/24 bars, T3 = 150 °C/55 bars and, T4 = 175 °C/95 bars. Ruminal, intestinal and total tract DM content, starch and N degradability of the extruded sorghum (T1, T2, T3, T4), unprocessed sorghum (T0; control) and barley grain (B) were determined using nylon bag and mobile bag techniques in a completely randomized block design (CRBD). Extrusion under T3 conditions increased in vitro ruminal digestibility, solubility ( a ), fractional disappearance rate ( c ) and effective degradability ( ED ) of DM and starch in sorghum to near similar to those of B. T3 also had higher (P E ) and extruded sorghum (S E ). Dry matter and N intakes were not affected by source of grain, but because of the higher starch content in sorghum, lambs on S E diet had greater starch intake (995 g/d) and higher (P E compared to B and BS E lambs which was reflected by the higher glucose concentration in the portal vein of S E lambs. Lambs fed S E diet also had greater ruminal microbial N (MN) yield (24.1 g/d), although ruminal pH and total VFA did not show any significant difference among treatments. Consequently, S E lambs recorded greater averaged daily gain (ADG) and more efficient (P E lambs. It can be concluded that extrusion under 150 °C/55 bars improves digestibility of sorghum starch and provides an option to completely replace barley in lambs.