title: Ruminal peptide concentration required to optimize microbial growth and efficiency.
abstract: Experimentation, with a single-phase continuous culture system operated at fractional dilution rates of 0.03 and 0.09 per hour and four cannulated crossbred steers (260 +/- 20 kg) used in a 4 x 4 Latin square design, was conducted to determine the level of ruminally degradable protein (RDP) that maximized microbial efficiency (MOEFF), microbial nitrogen flow, and nutrient digestibility in the rumen. Treatments consisted of increasing diet RDP levels (from 3.5 to 17.5% RDP on a DM basis). The basal diet was corn with casein or soybean meal used as the source of RDP in the continuous culture experiment 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 nitrogen 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 < 0.05) only for the 0.09/h dilution rate. Microbial efficiency was not influenced 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 concluded from this research that the RDP requirement of NSC-fermenting bacteria was lower than that currently fed in many diets.
authors.affiliation: Department of Animal Sciences, University of Missouri, Columbia 65211, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Fu
authors.forename: E E
authors.initials: EE
authors.lastname: Felton
authors.forename: J W
authors.initials: JW
authors.lastname: Lehmkuhler
authors.forename: M S
authors.initials: MS
authors.lastname: Kerley
mesh_terms: D000818:Animals; D002364:Caseins; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D004063:Digestion; D005285:Fermentation; D066298:In Vitro Techniques; D008297:Male; D010455:Peptides / Q000378:metabolism*; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism / Q000382:microbiology*; D013025:Glycine max; D003313:Zea mays
chemical_list: D002364:Caseins; D010455:Peptides