Marcadores e função dos microrganismos ruminais aderidos a partículas de forragem

Abstract

The first part of this present study a set of trials were conduct to evaluate digestibility and the potential of different markers for estimating the microbial mass adhered to forage particles incubated in vitro during 24 hours at different pH. The experiment was conducted in a completely randomized experimental design in a 2×4 factorial arrangement, testing the effect of two forages (Tifton hay and ryegrass) and 4 values of initial pH (5.5, 6.0, 6.5 and 7.0). On average, forage degradation were higher for ryegrass than for Tifton hay (P<0.05) and linearly and positively affected (P<0.05) by increased pH. P and purines were the markers that showed correlation (P<0.05) with forage degradation. In the second part of this study, two experiments were conducted to evaluate the interactive role of bacteria and fungi on forage degradation in vitro in medium containing or not of antimicrobial solutions: Antibiotic (Ab) - A mixture of three antibiotics; Antifungal (Af); Positive control (C+) - with both Ab and Af and Negative control (C-) - without antimicrobials. The first experiment in vitro 3 trials were conducted in a completely randomized experimental design in a 2×4 factorial arrangement, testing the effect of two forages (Tifton hay and ryegrass) and 4 incubation medium. The variables evaluated were forage digestibility, and microbial adherence to forage particles and enzymatic activity from the forage residue incubated during 24 hours. The second experiment it was conducted three in vitro gas trials in a completely randomized experimental design in a 2×4×8 factorial arrangement, testing the effect of two forages (Tifton hay and ryegrass), 4 incubation medium and 8 incubation times (3, 6, 9, 12, 24, 36, 48 e 72 hours). The results from the first experiment indicate there was incubation media x forage type interaction for dry matter and FDN degradability (P<0.05). Compared to negative control, the positive control or only Ab addition decreased dry matter and FDN degradability, xylanase activity and phosphate the concentration of decrease (P<0.05). The addition of only Af in the incubation medium did not affect any variable compared to negative control. In the second experiment there was media incubation x forage type x incubation time interaction for gas production variable (P<0.05). The accumulate gas production when was add only Af in the incubation medium had similar gas volume compared to negative control, and both medias presented higher values compare to Ab and C+ (P<0.05). However, for Tifton hay the addition of Ab showed that the accumulated gas volume was higher than C+ (P<0.05) after 24 hours. The results indicate that phosphate and purines can be used to estimate microbial adherence to forage particles, with phosphate having analytical and cost advantages over the other markers. At fixed 24 hours in vitro incubation bacteria activity was more relevant on determining forage degradation. In 72 hours of in vitro fermentation bacteria also had the most important role on forage degradation, however, was increased by fungi activity.