Ruminal peptide concentration required to optimize microbial growth and efficiency

Experimentation, with a single-phase continuous culture system operated at fractional dilution rates of 0.03 and 0.09 per hour and four cannulated cro ssbred steers (260 +/- 20 kg) used in a 4 x 4 Latin square design, was cond ucted to determine the level of ruminally degradable protein (RDP) that max imized microbial efficiency (MOEFF), microbial nitrogen flow, and nutrient digestibility in the rumen. Treatments consisted of increasing diet RDP lev els (from 3.5 to 17.5% RDP on a DM basis). The basal diet was corn with cas ein or soybean meal used as the source of RDP in the continuous culture exp eriment and animal study, respectively. Dietary nonstructural carbohydrate (NSC) ranged from 52 to 75% on a dry matter basis. Urea was added to ensure an adequate ammonia nitro-gen source for microbial growth. The RDP levels did not affect true digestibility of dry matter and organic matter, ruminal pH, particulate passage rate, or liquid passage rate in the animal study. As RDP increased, bacterial nitrogen production increased linearly (P < 0.0 5) only for the 0.09/h dilution rate. Microbial efficiency was not influenc ed by RDP level. Ruminal peptide and NH3 N concentration increased linearly (P < 0.05) as RDP increased. Based on this experimentation, 1.8 mM peptide maximized MOEFF when ammonia nitrogen was not limiting (> 2 mg/dL). We con cluded from this research that the RDP requirement of NSC-fermenting bacter ia was lower than that currently fed in many diets.