Nitrogen source and concentration affect utilization of glucose by mixed ruminal microbes in vitro.

The availability of rumen-degradable protein (RDP) changes the use of carbohydrates by ruminal microbes. However, the effects of RDP on the simultaneous use of carbohydrate and formation of microbial products are not well described, although such information is needed to understand the potential effect on nutrient supplies for ruminants. The objective of this in vitro study was to compare the effects of different levels of RDP (0.15, 0.31, 0.46 g of N/L) from tryptone (Tryp) or urea (Ur) on product formation from glucose in fermentations with mixed ruminal microbes. The study had a randomized complete block design with 2 replicated fermentation runs and destructive sampling at 0, 0.5, 1, 2, 3, 4, and 5 h. All rates given are first-order rate constants. Glucose disappearance rates and organic acid carbon (C) production rates tended to be or were greater for Tryp (0.64 and 0.58 h