USAGE OF CONTINUOUS PRESSURE READER IN IN VITRO GAS PRODUCTION TECHNIQUE FOR EVALUATION OF FEEDSTUFFS FOR RUMINANTS

This experiment was conducted to determine possibility of usage of automatic system that continuously record pressure and sample gas at certain intervals in in vitro gas production technique. Rumen fluid was collected from 2 ruminally cannulated Holstein heifers weighing an average of 400 kg. Medium was prepared by mixing macromineral (200 ml), micromineral (0.1 ml), buffer (200 ml), reduction (40 ml) and resazurin (1 ml) solutions as well as distilled water (400 ml). The mixtures contained alfalfa hay, maize silage, wheat, maize, cottonseed meal, and soybean meal. Mixtures differing in the roughage:concentrate ratio (20:80, 40:60, 60:40, and 80:20) were formulated to contain rapidly fermentable fraction (B1+B2), insoluble but slowly fermentable fraction (B3,) and 50% of these fractions at three different fermentation characteristics. Gas productions at 6, 12, 24, and 48 h relative to incubation determined using system recording continuously. In automatic system, "dual-pool logistic equation" representing factions either soluble in NDF solution and rapidly fermentable fraction (NDF-F) and fractions or insoluble in NDF solution, but slowly fermentable (NDF-S) were used. The fermentation was completed within 12 h in fully automatic system. While cumulative gas production from NDF-F was positively correlated with gas production within 3 h (r=0.77, P<0.001), cumulative gas production from NDF-S was positively correlated with gas production within 3-20 h (r=0.88, P<0.001). Differences in time to reach maximal fermentation rate from NDF-F and NDF-S increased with increasing NDF (r=0.76, P<0.001) and ADF (r=0.85, P<0.001) levels. These data suggest that fermentation kinetics parameters, such as lag time and time to reach maximal fermentation rate from fractions soluble and insoluble in NDF solution, should be considered in formulation and evaluation of rations.