População microbiana ruminal e atividade celulolítica de fungos provenientes de bovinos leiteiros alimentados com diferentes forragens

Abstract

This study aimed to evaluate the physical and chemical characteristics and microbiota of rumen fluid of Holstein cows and heifers fed with different tropical forages in the North of Minas Gerais. Thirty samples of rumen fluid were collected from cows fed withsorghum silage and 32 from cows fed with Brachiaria brizantha pasture. Twelve rumenfluid samples from heifers fed with sorghum silage and eleven from heifers fed with sugar cane were also collected. After the collection, direct exams using stained slides through Grams method and mycological detection after clearance with KOH were performed. The culture for aerobic microorganism detection was performed in Sabouraud agar, MacConkey agar and C media containing 1% microcrystallinecellulose. The Enterobacteriaceae genus and yeast species were identified, considering its micromorphological, physical and chemical characteristics. This identification was confirmed on yeast based on the sequence analysis of ribosomal DNA. The isolates of mycelial fungal were identified using the micro culture technique and visualization of the micromorphological and reproductive characteristics in the optical microscopy. The cellulolytic activity of these fungi was evaluated after theisolated colony growth and measurement of the cellulose degradation halo in the C medium. The obtained data from the direct mycolological exam indicated the presence of fungi structure in 100% of the samples from cows fed with B. brizantha. However, this positivity tax was significantly lower for cows fed with sorghum silage (33%). TheEnterobacteriacea and yeast populations in the rumen liquid of heifers fed with sugar cane were significantly higher when compared to those from other evaluated groups. In these animals, the soluble carbohydrate from the sugar cane could be enabling the growth of these microbial groups. However, these heifers presented lower concentration of mycelial fungi in the sampled rumen liquid that could be under negative interactions such as competition and antagonism promoted by bacteria and yeasts. One hundred isolates of Enterobacteriacea were identified, showing the predominance of the genus Klebsiella (28%), Enterobacter (26,7%) and Proteus (21,3%). The majority of these bacteria are pathogenic for humans and animals; however, they could consume the rumen oxygen and ferment soluble carbohydrates in the rumen. Thirty eight yeast isolates from the evaluated animal rumen were identifiedand the most frequent species was Candida krusei, which is an important agent of opportunistic mycosis in animals and humans and presents intrinsic and acquired resistance to different antifungal drugs. Among the obtained mycelial fungi, the most frequent genus were Aspergillus (56%), Rhizophus (13%), Trichophyton (8%), Paecilomyces (6,7%), and Scedosporium (6%). The cellulolytic activity was significantly higher for the genus Aspergillus, indicating the biotechnological potentialof these microorganisms in several research areas, animal and industrial productions. Heifers fed with sugar cane presented more alterations in these microorganism populations. Future studies should unveil these differences concerning the carbohydrate sources present in the tropical forages and in the animal categories. The ecological or pathogenic role of these microorganisms should also be consideredaiming better productivity and animal health.