Effect of roasting on ruminal degradation, intestinal digestibility and absorbable amino acid profile of cottonseed and soybean

The effect of heat processing on ruminal degradation, intestinal digestibility (UDP-D) and absorbable amino acid (AA) profile of cottonseed oilcake (CSOC) and soybean oilcake (SBOC) was calculated. CSOC and SBOC were roasted in a drum roaster at six temperature settings and five time intervals resulting in 30 treatments per feedstuff. Percentage acid detergent insoluble nitrogen (% ADIN) was used as a screening test. Ruminal protein degradation and UDP-D were measured with the in situ polyester and mobile bag techniques (MBT), respectively. Temperature and time altered (P < 0.05) crude protein (CP) disappearance from the rumen and total tract, as well as UDP-D. The % ADIN and the theoretical amount of AA available increased, whereas effective ruminal protein degradability decreased with temperature and time. The relationship between total N disappearance and % ADIN (R2 = 0.99) for CSOC was non-linear (P < 0.05); for SBOC it was linear (P < 0.05) (R2 = 0.85). The relationship between UDP-D and % ADIN (R2 = 0.99) for CSOC was non-linear (P < 0.05); for SBOC it was linear (P < 0.05) (R2 = 0.86). Heat processing decreased (P < 0.05) Lys in both CSOC and SBOC. The AA Thr, Pro and Gly in CSOC and Thr, Val, Leu, His, Asp, Gly and Ala in SBOC, were more (P < 0.05) resistant to rumen degradation; more Thr and Lys (P < 0.05) were absorbable in both CSOC and SBOC, when compared to the control. CSOC and SBOC should be treated at 150 °C/40 min and 130 °C/45 min respectively.