| Resumo: |
The flow of ruminal undegradable protein (RUP) to the small intestine can be increased if ruminal degradation of dietary protein is reduced. The objective of this study was to evaluate the effect of extrusion on ruminal degradability of dry matter (DM) and crude protein (CP) from dehulled lupin (Lupinus albus L.) (DL) and rapeseed (Brassica napus L.) meal (RM). Unextruded soybean (Glicine max L.) meal (SBM) was used as a control. The DL was extruded at 130 ºC with 20% moisture and RM was extruded at 120 ºC with 20% moisture. Ruminal degradability was evaluated in situ by incubating feed samples for 2, 4, 8, 12, 24, and 48 h of fermentation in the rumen using three rumen-fistulated dairy cows. Values of CP soluble fraction (a) in SBM, DL, extruded dehulled lupin (EDL), RM, and extruded rapeseed meal (ERM) was lower in the extruded feeds (P < 0.05). The slowly degradable fraction (b) of SBM, DL, EDL, RM, and ERM was 858, 593, 622, 451, and 457 g kg-1, respectively, and was increased by extrusion (P < 0.05). Extrusion reduced the effective degradability (ED) of CP in lupin from 807 to 788 g kg-1; k p = 0.05 h-1 while ED was reduced from 868 to 789 g kg-1; k p = 0.05 h- 1 in ERM. This resulted in an increase in RUP of 8.95% in EDL (P < 0.05); the increase was 37.35% (P < 0.05) in ERM. It may be concluded that extrusion in the presence of moisture reduced the degradability of CP, particularly in the case of ERM.
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