Protein degradability of soybean meal coated with different lipid substances and its effects on ruminal parameters when included in steer rations

The coating of soybean meal with lipid substances as a protective method against bacterial degradation in the rumen was studied in two experiments. Substances used as coating agents were fish oil (FO), beef tallow (BT) and soap-stock (SS). In Trail 1, degradability studies by using nylon bags method were performed on uncoated soybean meal (T0) or soybean meal coated with 5% FO (T1), 10% FO (T2), 20% FO (T3), 5% SS (T4), 10% SS (T5), 20% SS (T6), 5% BT (T7), 10% BT (T8) and 20% BT (T9). Coating soybean meal with 20% FO (dry matter basis) significantly reduced the soluble protein fraction (P≤0.05), from 20.8 (T0) to 12.5% (T3), but the insoluble protein fraction was not affected. The use of 20% SS decreased (P≤0.05) both soluble and the degradability of the insoluble protein fractions from 20.8 and 76.7% (T0) to 9.3 and 59.2% (T6), respectively. The use of 10 and 20% BT (T8 and T9) decreased (P≤0.05) only the soluble protein fraction from 20.8 (T0) to 10.3 and 6.9%, respectively. In Trial 2, soybean meal coated with 20% SS, considered the best treatment for protecting soybean meal from rumen degradation in the present experiment, was included in a diet for rumen fistulated steers. The diet was composed of alfalfa hay (10%), wheat straw (50%), ground corn (20%) and non-coated (T0) or coated soybean meal (T1) (20%). Ruminal content samples were obtained at 0, 2, 4, 6 and 8 h postprandial and pH, ammonia–nitrogen (NH3–N) and volatile fatty acids (VFA) were determined in order to evaluate the effects of protection. When coated soybean meal was included (T1) non-significant differences were found between T0 and T1 for pH and VFA concentration (total or individual). However, there was a significant reduction (P≤0.05) of NH3–N concentration of 21, 25 and 27.5% at 2, 4 and 6 h postprandial, respectively