title: Net absorption and utilization of nitrogenous compounds across ruminal, intestinal, and hepatic tissues of growing beef steers fed dry-rolled or steam-flaked sorghum grain.
abstract: Our objectives were to determine effects of grain processing on splanchnic (gut tissues and liver) N metabolism and whole-body N balance by growing steers and to ascertain the relative contributions of ruminal and intestinal tissues to net absorption and utilization of N-containing nutrients. Seven beef steers (348 kg initial BW), surgically implanted with appropriate catheters, were fed diets containing 77% steam-flaked (SF) or dry-rolled (DR) sorghum grain. Blood flows and net output or uptake of ammonia N, urea N, and alpha-amino N (estimate of amino acids) were measured across portal-drained viscera (PDV or gut tissues) and intestinal, ruminal, hepatic, and splanchnic tissues (PDV + hepatic). The experimental design was a crossover between DR and SF diets, with six samplings of blood at 2-h intervals on 2 d for each steer. Nitrogen intake (139 +/- 3 g/d), output in urine (43 +/- 2 g/d), and retention (40 +/- 3 g/d) were similar for both processing treatments. When steers were fed SF sorghum compared to DR sorghum, N retention as a percentage of N intake was numerically greater (P < 0.12), output of fecal N was numerically lower (P < 0.13), and urinary urea N was lower (P < 0.04). For SF vs DR, net uptake of alpha-amino N by liver was higher (P < 0.04; 20 vs 9 g/d) and was numerically lower (P < 0.16) for ruminal tissues (15 vs 33 g/d). Feeding steers SF compared to DR tended to increase net transfer (cycling) of blood urea N to PDV (57 vs 41 g/d; P < 0.07), increased cycling to intestinal tissues (15 vs 6 g/d; P < 0.05), and numerically increased transfer to ruminal tissues (42 vs 32 g/d; P < 0.12) but did not alter other net output or uptake of N across splanchnic tissues. Total urea N transfer (blood + saliva) was similar for both treatments. Net uptake of alpha-amino N by ruminal tissues was about 30% of the net amount of alpha-amino N absorbed across the intestinal tissues. In summary, most of the blood urea N cycled from the liver to gut tissues was transferred to ruminal tissues for potential microbial protein synthesis, and the net ruminal utilization of alpha-amino N was about 30% of that absorbed from intestinal tissues. Feeding growing steers SF compared to DR sorghum diets numerically increased whole-body N retention (percentage of N intake) by about 15% and tended to increase transfer of blood urea N to the gut by about 40%, which could increase the supply of high-quality microbial protein for absorption.
authors.affiliation: Department of Animal Sciences, University of Arizona, Tucson 85721, USA. lgsmith@ag.arizona.edu
authors.forename: C B
authors.initials: CB
authors.lastname: Theurer
authors.forename: G B
authors.initials: GB
authors.lastname: Huntington
authors.forename: J T
authors.initials: JT
authors.lastname: Huber
authors.forename: R S
authors.initials: RS
authors.lastname: Swingle
authors.forename: J A
authors.initials: JA
authors.lastname: Moore
mesh_terms: D000042:Absorption; D000596:Amino Acids / Q000378:metabolism; D000641:Ammonia / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001806:Blood Urea Nitrogen; D002417:Cattle / Q000254:growth & development / Q000378:metabolism*; D018592:Cross-Over Studies; D004032:Diet / Q000662:veterinary*; D002523:Edible Grain / Q000378:metabolism; D005243:Feces / Q000737:chemistry; D005511:Food Handling / Q000379:methods; D007413:Intestinal Mucosa / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D009584:Nitrogen / Q000097:blood / Q000378:metabolism*; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism*; D013152:Splanchnic Circulation; D014508:Urea / Q000378:metabolism
chemical_list: D000596:Amino Acids; D000641:Ammonia; D014508:Urea; D009584:Nitrogen