Abstract
The present study was aimed at understanding a shift in rumen microbiome of buffaloes fed various levels of total digestible nutrients. To understand the process, the metagenomics of rumen microbes, in vivo and in vitro rumen fermentation studies were carried out. Three rumen fistulated adult male Murrah buffaloes were fed three isonitrogenous diets varying in total digestible nutrients (70, 85 and 100% of TDN requirement) in 3X3 switch over design. On dry matter basis, wheat straw/ roughage content were 81, 63 and 51% and that of maize grain was 8, 16 and 21% in three diets respectively. After 20 d of feeding, rumen liquor and rumen contents were sampled just before (0h) and 4h post feeding. Ruminococcus flavefaciens and R. albus (estimated with real time PCR) were higher in high roughage diets. The predominant phyla in all the three groups were Bacteroidetes, Firmicutes followed by Proteobacteria, Actinobacteria and Fibrobacteres. A core group of more than fifty rumen bacteria was present in all the animals with very little variations due to level of TDN. The most predominant bacterial genera reported in order of decreasing abundance were: Prevotella, Bacteroides, Clostridium, Ruminococcus, Eubacterium, Parabacteroides, Fibrobacter, Butyrivibrio etc. The higher diversity of the enyzmes families GH 23, GH 28, GH 39, GH 97, GH 106, and GH 127 (the enzymes active in fibre and starch degradation) were significantly higher on 100%TDN diet while CE 14 (required for the hydrolysis of bond between carbohydrate and lignin) was higher on low TDN (70%) diet, indicating ester bond cleavage was better in animals fed high roughage (wheat straw) diet.
Highlights
In most of the tropical countries, the ruminants are fed on lignocellulosic crop residues like cereal straws, stovers, sugarcane bagasse, oil cakes with small quantities of cereal grain and green fodder as protein and energy sources
The composition of diet and the post-feeding period affect pH of rumen content which was significantly higher at 85% total digestible nutrients (TDN) diet as compared to 70% TDN diet but was similar to 100% TDN diet irrespective of sampling time, pH dropped significantly after 4h post feeding as compared to 0h in all the three diets (Table 2)
A higher F/B ratio in high fiber groups was positively correlated with higher Ruminococcus population in these groups indicates that these microbes are essentially required for fiber degradation
Summary
In most of the tropical countries, the ruminants are fed on lignocellulosic crop residues like cereal straws, stovers, sugarcane bagasse, oil cakes with small quantities of cereal grain and green fodder as protein and energy sources. The bioconversion of these poorly utilizable energy sources lead to the formation of utilizable form of energy The recent studies based on real time PCR and meta-transcriptomic analysis have reported several hundred enzyme components which act collectively and synergistically upon complex fibrous feed material [3]. Hundreds of genes active in degradation of cellulose have been identified belonging to various CAZy families from the rumen carbohydrate active enzyme database (CAZyme database)
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