title: Histidine utilization by growing steers is not negatively affected by increased supply of either ammonia or amino acids.
abstract: Two experiments were conducted with ruminally cannulated Holstein steers to determine effects of N supply on histidine (His) utilization. All steers received 2.5 kg DM/d of a diet based on soybean hulls; abomasal infusion of 250 g/d amino acids, which supplied adequate amounts of all essential amino acids except His; abomasal infusion of 300 g/d glucose; and ruminal infusion of 180 g/d acetate, 180 g/d propionate, and 45 g/d butyrate. Both experiments were 6 x 6 Latin squares with treatments arranged as 3 x 2 factorials. No significant (P < 0.05) interactions between main effects were noted for N balance criteria in either Exp. 1 or 2. For Exp. 1, steers (146 +/- 7 kg) received 0, 1.5, or 3 g/d of L-His infused abomasally in combination with 0 or 80 g/d urea infused ruminally to supply a metabolic ammonia load. Urea infusions increased (P < 0.05) ruminal ammonia concentration from 8.6 to 19.7 mM and plasma urea from 2.7 to 5.1 mM. No change in N retention occurred in response to urea (35.1 and 37.1 g/d for 0 and 80 g/d urea, respectively, P = 0.16). Retained N increased linearly (P < 0.01) with His (31.5, 37.8, and 39.0 g/d for 0, 1.5, and 3 g/d L-His, respectively). Efficiency of deposition of supplemental His between 0 and 1.5 g/d averaged 65%. In Exp. 2, steers (150 +/- 6 kg) were infused abomasally with 0 or 1 g/d of L-His in combination with no additional amino acids (Control), 100 g/d of essential + 100 g/d of nonessential amino acids (NEAA+EAA), or 200 g/d of essential amino acids (EAA). Retained N increased (P = 0.02) from 34.2 to 38.3 g/d in response to His supplementation. Supplementation with NEAA+EAA increased (P < 0.05) N retention (33.9, 39.3, and 35.6 g/d for Control, NEAA+EAA, and EAA, respectively), likely in response to increased energy supply. Plasma urea concentrations of steers receiving NEAA+EAA (3.8 mM) and EAA (3.8 mM) were greater (P < 0.05) than those of Control steers (2.7 mM). The average efficiency of His utilization was 63%, a value similar to the value of 65% observed in Exp. 1, as well as the 71% value predicted by the Cornell net carbohydrate and protein system model. Under our experimental conditions, increases in N supply above requirements, as either ammonia or amino acids, did not demonstrate a metabolic cost in terms of His utilization for whole-body protein deposition by growing steers.
authors.affiliation: Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600, USA.
authors.forename: K C
authors.initials: KC
authors.lastname: McCuistion
authors.forename: E C
authors.initials: EC
authors.lastname: Titgemeyer
authors.forename: M S
authors.initials: MS
authors.lastname: Awawdeh
authors.forename: D P
authors.initials: DP
authors.lastname: Gnad
mesh_terms: D000018:Abomasum / Q000378:metabolism*; D000596:Amino Acids / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D000641:Ammonia / Q000008:administration & dosage / Q000378:metabolism / Q000494:pharmacology*; D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001806:Blood Urea Nitrogen; D001823:Body Composition / Q000187:drug effects; D002417:Cattle / Q000254:growth & development* / Q000378:metabolism*; D004063:Digestion; D006639:Histidine / Q000378:metabolism*; D008297:Male; D011897:Random Allocation; D013025:Glycine max
chemical_list: D000596:Amino Acids; D006639:Histidine; D000641:Ammonia