IN VITRO DEGRADATION OF CORN STOVER WITH MIXED CULTURES OF RUMEN BACTERIA

Abstract

With the development of a mixed culture of rumen bacteria with high capability of corn (Zea mays L.) stover degradation, we hope to have live inoculum microorganisms whose activity inside the rumen of inoculated animals increases the feed efficiency of diets based on agricultural by-products high in fiber. Two experiments were conducted to evaluate degradation of corn straw by mixed culture (MC) of rumen bacteria. In Experiment 1 rumen fluid was collected from a Holstein bull (850 kg BW) and a sheep (45 kg BW) fed corn straw and alfalfa (Medicago sativa L.) hay or concentrate. Rumen fluid (1 mL) was inoculated in a sterile culture medium (9 mL), using corn straw or cellulose as a carbon source and incubated at 39 °C, then they were reinoculated every 72 h during 15 days. From 17 MC obtained, seven were selected and the effect of corn straw concentration in the culture medium (0.5 or 1.0 %) was analyzed using a completely randomized design. In Experiment 2 rumen fluid from three Holstein cows (650 kg average BW) and three sheep (45 kg average BG) were obtained, and the cultures were reinoculated every day during 15 days, in order to determine the effect of donor, using a completely randomized design. Corn straw degradation was the variable measured in both experiments. In Experiment 1, corn straw degradation decreased (p0.001; 13.49 vs. 8.17 mg/mL of medium), which indicated that degradation capacity of a MC may be underestimated when the corn straw concentration in the culture medium is too high (1.0 %). The MC1 from sheep and enriched on corn straw medium, showed a larger degradation (54.98 %; p