Effects of Dietary Effective Fiber to Rumen Degradable Starch Ratios on the Risk of Sub-Acute Ruminal Acidosis and Rumen Content Fatty Acids Composition in Dairy Goat

This study investigated the effects of dietary physical effective NDF (peNDF, g/kg of DM) to rumen degradable starch (RDS, g/kg of DM) ratios (PRR) on the risk of sub-acute ruminal acidosis (SARA), bacterial density, and rumen content fatty acid (FA) composition in dairy goats. Six ruminally cannulated dairy goats were assigned to 3 treatments in a repeated 3×3 Latin square design. Treatment diets consisted of three PRR levels: 1.81, 1.43, and 1.21, which were achieved by replacing dietary corn with wheat (0, 175, and 350g/kg of DM). Diets with similar starch contents and identical forage to concentrate ratio (50:50) were used. The time and the area with a ruminal pH below 5.8 (from 2.97 to 7.17h/d, and from 0.73 to 1.33 pH×h/d, respectively) or below 5.6 (from 1.20 to 3.05h/d, and from 0.11 to 0.20 pH×h/d, respectively) linearly increased when the dietary PRR was reduced. With the reducing of dietary PRR, the molar ratio of acetate decreased, whereas that of propionate increased. However, the total VFA concentration showed a quadratic change in response to the dietary PRR. Reducing the dietary PRR caused a linear decrease in the rumen concentrations of iso C14:0, iso C15:0, anteiso C15:0, and iso C17:0. However, the C18:1 isomers concentration remained constant. The relative abundance of Ruminococcus albus and Streptococcus bovis was not affected by the dietary PRR, whereas that of Ruminococcus flavefaciens decreased with decreasing dietary PRR. These results suggested that the odd and branched FA content of the rumen might be used to determine the fluctuation of the ruminal pH and of the bacterial population. In addition, the recommended dietary PRR for dairy goats was 1.43.