In vitro gas production kinetics and digestibility in ruminant diets with different levels of cashew nut shell liquid

The aim of this study was to evaluate the effect of increasing levels of cashew nut shell liquid (CNSL) in ruminant diets on in vitro dry matter digestibility (IVDMD), gas production kinetics, ruminal fermentation parameters, ammoniacal nitrogen concentration (NH3-N), and pH of the artificial rumen contents. The experimental design was completely randomized in a factorial 5 x 4 + 1 design, with five concentrate levels (200, 400, 600, 800, and 1,000 g kg-1 DM) and four CNSL levels (0, 0.3, 0.6, and 1.2 g kg-1 DM), as well as a control diet comprising only whole-plant corn silage, totaling 21 treatments. The inclusion of concentrate linearly increased IVDMD, while CNSL levels showed a quadratic effect, with the maximum estimated at 0.5 g kg-1 of CNSL. The total gas production, the disappearance of the substrate, the fraction of slow degradation (fraction VF2), and the respective degradation rate (fraction µ2) linearly increased with increasing levels of concentrate in the diet. Increasing concentrate levels resulted in a linear increase in the concentration of NH3-N and a reduction in the pH of the rumen liquid. Increasing CNSL levels decreased the concentration of NH3-N and increased the ruminal pH. The inclusion of 0.5 g CNSL kg-1 in the ruminant diets improved IVDMD, without altering the kinetic parameters of ruminal fermentation. The addition of CNSL to ruminant diets reduces ammoniacal nitrogen production and can avoid drastic reductions in ruminal pH, favoring better fermentation in the rumen.