Effects of conditioning temperature and time during the pelleting process on feed molecular structure, pellet durability index, and metabolic features of co-products from bio-oil processing in dairy cows

The objectives of this study were to systematically determine effects of conditioning temperature (70, 80, and 90°C), time (50 and 75 s), and interaction (temperature × time) during the pelleting process on co-products from bio-oil processing (canola meal) in terms of processing-induced changes on (1) protein molecular structure, (2) pellet durability index, (3) detailed chemical profile, (4) metabolic features and fractions of protein and carbohydrate, (5) total digestible nutrients and energy values, and (6) rumen degradable and undegradable content. Pellet durability was increased with increasing conditioning time. Chemical and carbohydrate profiles of co-products were not altered by pelleting process under different conditioning temperatures and times. With regard to protein fraction profiles, pellets conditioned for 50 s had higher soluble crude protein (SCP) and lower neutral detergent insoluble crude protein (NDICP) contents than those conditioned for 75 s (21.7 vs. 20.1% SCP, 16.0 vs. 16.5% NDICP, respectively). Total digestible nutrients and energy values were not altered by processing. Samples conditioned for 50 s had a higher content of rapidly degradable protein fraction (PA2) than those conditioned for 75 s (21.7 vs. 21.1% crude protein). In addition, the slowly degradable true protein fraction (PB2) was affected by the interaction of conditioning temperature and time. However, carbohydrate fractions did not differ with different conditioning temperatures and time. Different temperatures and time of conditioning during pelleting process greatly affect protein profiles without altering carbohydrate profiles. Molecular structure analyses also showed that pelleting altered inherent protein molecular structures of the co-products from bio-oil processing. Future study is needed to detect how molecular structure changes affect nutrient availability in dairy cattle.