Effect of pelleting at different conditions on ruminal degradation kinetics and intestinal digestion of canola meal in dairy cattle
Pelleting has been adopted and widely used in the animal feed industry with its positive improvements in feed quality. Canola meal, an important protein source for ruminants in Canada, is usually prepared in mash or in pellets in feed mills. The objective of this study was to investigate the effects of pelleting at different conditions on in situ ruminal degradation kinetics and in vitro intestinal digestion of canola meal. Two batches of canola meal were pelleted after conditioning at different temperatures (70, 80 and 90°C) for different time (30s and 60s). Five rumen-cannulated lactating Holstein cows were used in an in situ trial to determine ruminal degradation kinetics. Intestinal digestibility was detected using a three-step in vitro method. Samples conditioned at 80°C had highest degradation rates (Kd) for crude protein (CP) and dry matter (DM) among pellets due to the quadratic effect of conditioning time (P<0.05). The soluble fraction (S) of protein in pellets was greater than that in the unprocessed mash (9.84 vs. 5.68 %CP, P<0.01). The unprocessed mash had a greater content of bypass CP (BCP) but a lower content of effectively degraded CP (EDCP) than pellets (BCP: 44.20 vs. 39.30 %CP; EDCP: 55.81 vs. 60.70 %CP), indicating pelleting reduced (P<0.01) BCP but increased (P<0.01) EDCP contents of canola meal. However, bypass carbohydrates (BCHO) and effectively degraded CHO (EDCHO) were not affected by pelleting. The unprocessed mash had a lower ratio of effective degradability of N to carbohydrates (ED_N/ED_CHO) than pellets (126.17 vs. 142.85; P<0.01). Conditioning temperature had a significant impact on ED_N/ED_CHO among pellets (P<0.05). In the in vitro trial, intestinal digestible protein (IDP) content was greater in the unprocessed mash than in pellets (113.28 vs. 94.85 g/kg DM, P<0.05), indicating that pelleting decreased IDP content of canola meal. There was no difference detected among samples on intestinal digestion characteristics for carbohydrates. In conclusion, pelleting increased ruminal degradation of protein while intestinal digestion of protein decreased in the current study. However, ruminal degradation and intestinal digestion characteristics of carbohydrates were not affected.
Keywords: Pelleting, canola meal, rumen degradation and intestinal digestion kinetics