Effects of Alternating High and Medium Concentrate Diets on Fermentation in a Semi-Continuous Rumen Culture System

A semi-continuous culture system was used to determine effects of percent dietary concentrate and method of feeding on in vitro fermentation. Treatments consisted of four feeding regimens 1) 85% concentrate: 85% concentrate diet fed at 0700 and 1900 h; 2) alternate: 85% concentrate diet fed at 0700 h and 55% concentrate fed at 1900 h; 3) 70% concentrate: equal mixture of the 85 and 55% concentrate diets fed at 0700 and 1900 h, and 4) 55% concentrate: 55% concentrate diet fed at 0700 and 1900 h. Total volatile fatty acid concentrations and molar proportions of propionate were highest for the 85% concentrate regimen with no differences among other treatments. Acetate (molar proportion) was lower for the high concentrate diet than for other treatments. Concentrations of fermentation liquor ammonia were 13.4, 11.7, 12.6, and 9.8 mg/100 ml for 85% concentrate, alternate, 70%, and 55% concentrate groups. Culture pH was similar for all treatments. Apparent organic matter digestibilities were 41.0, 40.1, 39.6, and 34.6% and true organic matter digestibilities were 46.3, 45.4, 44.4, and 39.5% for 85% concentrate, alternate, 70%, and 55% concentrate regimens. Bacterial numbers were 1.06, 1.33, .86, and .85 × 10⁹ per ml.