COMPARISON OF FIBROUS MATERIALS AS MODIFIERS OF INSITU RUMINAL DEGRADATION OF CORN GLUTEN MEAL

Degradability of com gluten meal protein in situ is grossly underestimated compared with in vivo measurements. To study the influence of com gluten meal mixed with different fibrous sources on in situ ruminal DM and CP degradation, bags containing meal alone or mixed with corn cobs, wheat straw, or sawdust, respectively, were suspended in the rumen of two lactating Holstein cows for 0, 4, 12, 24, 48, 72, or 120 h. The three fibrous sources also were incubated alone to determine their degradation pattern. Cytosine was used as a bacterial marker to correct the in situ residues for bacterial contamination. Sawdust was almost completely resistant to ruminal degradation, and straw was slowly degraded to a final extent of 35.3% of total DM. The DM in com cobs had a degradable fraction of 63.7% and a rate of disappearance higher than that of corn gluten meal incubated alone. The DM and CP degradation rates of meal were not modified when feed was mixed with com cobs. Incubation with straw and sawdust increased rate of disappearance of DM and CP of com gluten meal (2.1 and 1.2%, respectively). Ruminal turnover was assumed to be 6%/h, and CP degradabilities of com gluten meal were 30.6 and 25.1% when the feed was incubated with straw and sawdust, respectively.