In vitro digestibility of Urochloa decumbens inoculated with fungi isolated from the gastrointestinal tract of sheep

Abstract

Pastures are the basis of ruminant feed; however, forage digestibility decreases in the dry season. In this study, the aims were to identify selected fungus isolates from the gastrointestinal tract of healthy Santa Inês sheep and to evaluate the in vitro digestibility of Urochloa decumbens (UD) hay inoculated with these fungi. Sequence analysis of the rDNA ITS regions and fragments of the encoding β-tubulin gene permitted identification of the isolate O45M1 as Aspergillus terreus. The isolate B13M2 was identified as Trichoderma longibrachiatum considering the sequence analysis of the ITS region and the gene encoding elongation factor 1-α. The coefficients of in vitro dry matter digestibility (DMD) and neutral detergent fibre digestibility (NDFD) of lignified UD were evaluated in ruminal fluid collected in three periods of 21 days. The ruminal fluid was inoculated with sterile Sabouraud broth (control), with A. terreus (O45 M1), with T. longibrachiatum (B13 M2), or with a mixture of these fungi. The DMD of hay was higher (p < .01, Fisher LSD test) when inoculated with the B13M2 isolate (47.31%) in comparison to the control (35.69%) for the three periods of collection of the ruminal fluid. The presence of mycelial fungi was detected in samples of the ruminal medium during three times of incubation (0, 24 and 72 h) in a ruminal simulator. Additionally, after the acid digestion, at 72 h of incubation, the population of mycelial fungi was significantly higher when the ruminal fluid was inoculated with isolate B13M2 (p < .05, Fisher LSD test), indicating resilience. B13M2 addition increases the DMD of lignified UD, showing potential for the development of probiotic or microbial additives for ruminants.