Effects of microwave irradiation on ruminal protein degradation and intestinal digestibility of cottonseed meal

The objectives of this study were to determine the effects of microwave irradiation on ruminal degradability and intestinal digestibility of crude protein (CP) and to monitor the fate of true proteins of cottonseed meal (CSM) in the rumen. Duplicate nylon bags of untreated or irradiated CSM (microwave power of 800 W for 2, 4 and 6 min) were suspended in the rumen of four non-lactating Holstein cows for up to 48 h, and resulting data were fitted to non-linear degradation model to calculate degradation parameters of CP. Proteins of untreated and treated CSM bag residues were fractionated by gel electrophoresis. Intestinal digestibility of CP was measured using the mobile nylon bag technique. From in situ results, microwave irradiation decreased (P < 0.05) the water soluble fraction and degradation rate, but increased the potentially degradable fraction of CP. The effective degradability of CP decreased (P < 0.05) as processing period increased. Irradiation for 2 and 4 min increased (P < 0.05) intestinal digestibility of ruminally undegraded CP, but extending to 6 min lowered (P < 0.05) the beneficial effect that 4 min had on intestinal CP digestibility. Electrophoretic results indicated that globulin 9S in untreated CSM (whereas globulin 9S, globulin 5S and albumin 2S in microwave irradiated CSM) make the bulk of escaped protein. Based upon these results, microwave irradiation at a power of 800 W for 4 min had the greatest potential to increase digestible undegraded protein.