Microbial populations, fermentative profile and chemical composition of signalgrass silages at different regrowth ages

Abstract

-Microbial populations, pH, ammonium nitrogen/total nitrogen (N-NH 3 ) ratio, concentrations of lactic acid, acetic acid and butyric acid and the chemical composition of Brachiaria decumbens cv. Basiliski silages at different regrowth ages (30, 40, 50, 60 and 70 days) were evaluated by using 2-kg capacity laboratory silos. It was used a 5 × 6 factorial scheme (5 regrowth ages × 6 fermentation periods) in a complete random design, with three replicates. The fermentation periods were 1, 3, 7, 14, 28 and 56 days. Lactic acid bacteria populations were recorded in fresh forage varying from 3.93 (30 days of regrowth) to 5.51 (70 days of regrowth) log colony-forming units (cfu)/g forage. Maximum populations of these microorganisms were recorded in the silages on the seventh day of fermentation (8.69 log cfu/g silage). Enterobacteria populations persisted until the 28 th day, with maximum values found as early as the first day of fermentation (7.89 log cfu/g silage). Levels of DM, NDF, ADF and ADIN increased linearly whereas values of CP decreased linearly with age of regrowth of the plants. There was a linear reduction in the levels of DM, CP and NDF and linear increase in the levels of ADIN over the period of fermentation. N-NH 3 level decreased and increased linearly with regrowth age and fermentation period, respectively. The pH decreased exponentially with fermentation period. Lactic acid increased and butyric acid decreased linearly with regrowth age. The predominant Lactobacillus plantarum species in signalgrass plants is Lactobacillus plantarum.Key Words: acetic acid, butyric acid, enterobacteria, lactic acid, lactic acid bacteria Populações microbianas, perfil fermentativo e composição bromatológica de silagens de capim-braquiária em diferentes idades de rebrotação RESUMO -Foram avaliadas as populações microbianas, o pH, a relação nitrogênio amoniacal/nitrogênio total (N-NH 3 ), as concentrações de ácidos láctico, acético e butírico e a composição bromatológica de silagens de Brachiaria decumbens cv. Basiliski de cinco idades de rebrotação (30, 40, 50, 60 e 70 dias) utilizando-se silos laboratoriais de 2 kg de capacidade. Utilizou-se um esquema fatorial 5 × 6 (5 idades de rebrotação × 6 períodos de fermentação), em um delineamento inteiramente casualizado, com três repetições. Os períodos de fermentação foram 1, 3, 7, 14, 28 e 56 dias. Na forragem fresca, foram registradas populações de bactérias do ácido láctico variando entre 3,93 (30 dias de rebrotação) e 5,51 (70 dias de rebrotação) log unidades formadoras de colônia (ufc)/g de forragem. Nas silagens, foram registradas populações máximas desses microrganismos no sétimo dia de fermentação (8,69 log ufc/g de silagem). As populações de enterobactérias persistiram até o 28 o dia, com os valores máximos observados logo no primeiro dia de fermentação (7,89 log ufc/g de silagem).

Microbial and fermentation profiles, losses and chemical composition of silages of buffel grass harvested at different cutting heights

“…Thus, the present study and other studies with tropical grasses (Santos et al, 2011;Pereira et al, 2007) have shown that the soluble carbohydrates present in plant tissue enable the development and predominance of LAB, resulting in a quick decline of the pH values and consequent inhibition of undesirable microorganisms. The silage pH values ranged (P<0.05) with the different cutting heights (Figure 2).…”

“…From the seventh day of fermentation, MY were no longer identified in the silage, except for the cutting height of 30 cm. Importantly, based on the silage pH values, the disappearance of these organisms was not expected, unlike what was observed by Pereira et al (2005), in elephant grass silage, and by Santos et al (2011), in signal grass silage. Probably, this disappearance is due to the reduced amounts of soluble carbohydrates in the silage, which may have inhibited the development of these microorganisms.…”

“…The peak development of LAB populations was observed on the third and on the seventh days of fermentation for the cutting heights from 40 (8.25 cfu/g) and on the seventh day of fermentation for the cutting heights from 50 cm (8.30 log cfu/g). The decrease in the microorganism population after this point is probably due to the reduced amount of carbohydrates for fermentation, which is a normal dynamics described in the literature for grass ensilage (Balsalobre et al, 2001;Santos et al, 2011). Pereira et al (2005) found that elephant grass plants had high initial concentrations of LAB (approximately 6 log cfu/g), also demonstrating that this group of bacteria became dominant over other groups in study.…”

“…This behavior was observed in the grass ensiled with 30 cm cutting height, in which the ENT population reached 5.87 log cfu/g on the fifteenth day after ensiling. Santos et al (2011) observed the disappearance of ENT in signal grass silages harvested at different ages only from the twentyeighth day after ensiling, which resulted in losses of more than 15% of total DM, regardless of regrowth age.…”

“…The grass cutting height directly influences the fermentation conditions that take place inside the silo, because the concentration of soluble carbohydrates, the dry matter (DM) contents and the microbial populations are altered as the age advances (Santos et al, 2011).…”