Currently, due to the expansion of the livestock farming integration system, many livestock
farms are also soybean producers, in this sense, the use of soybean in natura (SGIN) in the diet
of ruminants is used as a strategy to increase productivity and profitability of the production
system. The aim of this study was to evaluate the ruminal fermentation of diets containing two
different concentrates (with and without SGIN) and varied ratios of concentrate and forage via
in vitro tests of total gas and methane gas (CH4) production with bovine inocula. (Experimental
model). The inoculum was obtained from three cattle weighing 550 ± 115 kg, fed forage and
concentrate. Ruminal fluid collection was performed with the aid of an esophageal probe. The
treatments were tested in a randomized block experimental design with a factorial arrangement
(5 x 2), with the factor being the inclusion or not of the soybean grain and the presence of varied
relations of concentrates and forages, making up 10 treatments and with 3 blocks. When
observing ruminal fermentation kinetics (Table 4), it was observed that the total gas production
(parameter A) was higher for diets formulated with concentrate containing soybean meal (C2)
and lower for diets containing SGIN (C1) as protein source, regardless of volume level.
Regardless of the inclusion of forage in the bed, higher gas production was observed in diets
containing soybean meal as a protein source, and lower values in beds with SGIN. The
fractional degradation rate (μ) showed higher values for treatments with higher proportions of
concentrate. Effective degradability reduced with increasing proportion of forage in the diet for
all passage rates and diets. A positive linear effect was observed for the percentage of
concentrate (P<0.05), with an increase in DM degradation as the percentage of concentrate in
the diet increased (Table 5). The concentrate formulated with SGIN had lower DM degradation
compared to soybean meal, at the levels of 50 and 75% of concentrate in the diet (P<0.05). The
curves of the cumulative gas production for the means of C1 and C2 showed a difference after
24 hours of incubation, in which the C1 concentrate presented lower curves than the C2
concentrate (Figure 2). Linear reduction in CH4 production occurred as an increase in the
percentage of concentrate (P<0.05) (Table 8). For levels of 50, 75 and 100% of concentrate
including SGIN, there is a reduction in CH4 production of 16.31; 19.63 and 22.53%,
respectively. Thus, it is concluded that the inclusion of SGIN as a protein source in the
concentrate reduces the fermentation of the diet, but improves its fractional digestion. SGIN
reduces fermentation after 24 hours of incubation due to reduced fiber degradation. The
introduction of SGIN in the diet of ruminants reduces methane production from levels of 50,
75 and 100% concentrate
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