title: Supplemental protein sources for steers fed corn-based diets: I. Ruminal characteristics and intestinal amino acid flows.
abstract: Five cannulated Holstein steers (302 +/- 23 kg) were used in a 4 x 4 Latin square design experiment with extra observations to evaluate the effect of supplemental protein source on postruminal flow and intestinal disappearance of N and amino acids (AA). Diets were formulated to contain 12.5% CP using cracked corn (70%), ground corn cobs (15%), and supplement (15%). Except for an all-urea supplemented control diet, 40% of the total dietary CP was supplied by soybean meal (SBM), a high ruminal escape soybean meal (SoyPLUS; SP), or a corn gluten meal/blood meal combination (CB; 50:50 on a CP basis). The steers were fed twice daily and DMI was restricted to 2.0% of initial BW. Supplementation with CB increased (P < .10) non-microbial N flow at the duodenum but tended to decrease microbial N flow such that no differences (P > .10) in total N flows at the duodenum were detected among treatments. The efficiency of microbial protein synthesis was not affected by treatment but was greatest for urea/and tended to decrease when SP and CB were fed (21.8, 20.5, 19.5, and 15.7 g of N/kg of OM truly digested for urea, SBM, SP, and CB, respectively). A possible shortage of ruminally degradable N, as evidenced by low ruminal NH3 N concentrations (3.6, 4.2, 3.9, and 2.1 mg/dL for urea, SBM, SP, and CB respectively), or other factors, may have limited microbial protein synthesis. However, microbial N flows averaged 60.0% of duodenal N flow across treatments. Duodenal flow of essential, nonessential, and total AA were similar (P > .10) among treatments and averaged 293, 361, and 653 g/d, respectively). Lysine and methionine flows did not differ (P > .10) and averaged 41.6 and 13.3 g/d, respectively. The source of supplemental protein had no impact (P > .10) on small intestinal disappearance of AA or total tract N disappearance. Feeding proteins resistant to ruminal degradation may have limited microbial protein production, resulting in a shift in the proportion of metabolizable protein arriving at the small intestine from dietary and microbial origins. These results suggest that corn-based diets may be limiting in ruminally degradable N, especially when high ruminal escape protein sources are fed as supplemental CP.
authors.affiliation: Department of Animal Sciences, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: P A
authors.initials: PA
authors.lastname: Ludden
authors.forename: M J
authors.initials: MJ
authors.lastname: Cecava
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D004032:Diet / Q000662:veterinary; D004044:Dietary Proteins / Q000008:administration & dosage*; D004386:Duodenum / Q000382:microbiology / Q000502:physiology*; D005527:Food, Fortified; D005769:Gastrointestinal Motility / Q000502:physiology; D008239:Lysine / Q000378:metabolism; D008297:Male; D008715:Methionine / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D012417:Rumen / Q000382:microbiology / Q000502:physiology*; D013025:Glycine max / Q000378:metabolism; D003313:Zea mays / Q000737:chemistry / Q000378:metabolism
chemical_list: D000596:Amino Acids; D004044:Dietary Proteins; D008715:Methionine; D008239:Lysine; D009584:Nitrogen