LAUSR

The objective of this study was to investigate the rumen dry matter (DM), starch and protein degradation kinetics of an Iranian corn grain (single crass 702) processed using different thermal processing methods including 1) grinding (G, 2mm), 2) super-conditioned pelleting (SCP; moisture 20%, retention time 6 min and conditioning temperature 95°C), 3) puffing (PUF; puffing temperature 200°C, hot air velocity 25 m/s, feed rate 100 g/m) and 4) extruding (EX; moisture 20%, temperature of melting zone 75°C and die zone 125°C and time 150s). Three lactating Holstein cows fitted with a ruminal cannula were used. Samples were incubated into the rumen for 2, 4, 8, 12, 24, and 48 h. Rumen degradation kinetics were fitted based on equations. Data were analyzed by GLM procedure of SAS (P < 0.05) using a completely randomized design with 6 replications for every treatment. Rapidly soluble fraction (a) and fractional rate constant (c) of DM were higher (P < 0.01) in PUF and EX corns than SCP. The lowest (P < 0.05) slowly degradable fraction (b) of DM was found in SCP. The highest (P < 0.01) effective rumen degradability of DM (ERDM), starch (ERDS) and protein (ERDP) were observed in the EX, followed by PUF, SCP and G corns. Fraction a of starch and protein was significantly greater (P < 0.01) in EX, PUF and SCP than G. The rate of degradability (c) of starch, DM and protein in EX and PUF were similar and higher (P < 0.01) than SCP and G, but c for starch in EX was greater (P < 0.01) than PUF and fallowed by SCP and G corns. In conclusion, the super-conditioning of corn as a new method of corn processing increased rapidly soluble fraction starch similar to PUF and EX corns and effective rumen degradability of starch was significantly increased in SCP corn.