Effects of different concentrate levels, types of non-fiber carbohydrates and fiber digestibility on the rumen ecosystem

The aim of this study was to characterize the population change of cellulolytic and amylolytic rumen bacteria, caused by the increase of concentrate, and by the use of different sources of NFC in diets with sugarcane silage. Samples of rumen contents were collected for subsequent analysis of the relative quantification of rumen microorganisms, from four research projects conducted at the Research Laboratory in Beef Cattle at FMVZ / USP - Pirassununga-SP. In all experiments, Nellore beef cattle, castrated, and ruminal cannulated, were used in a Latin square design. Three cellulolytic bacteria (Fibrobacter succinogenes, Ruminococcus albus and Ruminococcus flavefaciens); two amylolytic (Streptococcus bovis and Ruminobacter amylophilus); and a lactate fermenting microorganism (Megasphaera elsdenii), were quantified by the technique of qPCR, to determine the effect of diet on the population of rumen microorganisms. Experiment 1, the experimental diets were formulated with two levels of concentrate: 60% or 80%, and the roughage used was sugarcane silage (IACSP 93-3046). Within each level of concentrate inclusion, three different sources of NFC were used: steam flaked corn (SFC), pelleted citrus pulp (PCP), or ground corn (GC). SFC and PCP were included in the diet in partial replacement of 70% of GC. Experiment 2, the experimental diets were formulated with 60% of concentrate level, and two sugarcane genotypes divergent for stalk NDFD, with high or low NDFD, either freshly cut or as silage. Experiment 3, the experimental diets were formulated with two levels of concentrate: 60% or 80%, and the roughage used was fresh sugarcane, with high or low NDFD. In the Experiment 1, increasing concentrate in the diet decreased the population of F. succinogenes (P<0.01) and S. bovis (P<0.01), and increased R. flavefaciens population (P=0.05). The partial replacement of GC by PCP increased S. bovis population (P=0.01) and decreased R. flavefaciens population (P<0.01). The replacement of GC by SFC decreased the population of R. albus (P<0.01). There was a significant Diet*NFC interaction only for M. elsdenii (P=0.02), where SFC increased the relative population only at the 80% concentrate diet. Experiment 2, Diets with fresh sugarcane increased the population of S. bovis (P <0.01), and M. elsdenii (P=0.06). There was a significant interaction between NDFD and conservation mode of sugarcane for F. succinogenes (P = 0.01), where sugarcane with high NDFD increased F. succinogenes population only when sugarcane was offered as freshly cut. In Experiment 3, the increase concentrate in the diet decreased S. bovis population (P<0.01), and increased R. amylophilus (P=0.07). There was a significant interaction between NDFD and concentrate level for F. succinogenes (P=0.06) and R. albus (P<0.01), where sugarcane with high NDFD increased the population of these microorganisms only at the 60% concentrate diet. The animal performance can be explained by modulation of the population of the rumen microorganisms through diet composition. (AU)