Splanchnic nitrogen metabolism by growing beef steers fed diets containing sorghum grain flaked at different densities.

Abstract

The objective of this study was to determine effects of processing method, dry-rolled (DR) vs steam-flaked (SF), and degree of processing (flake density, FD) of SF sorghum grain on splanchnic (gut and liver) N metabolism by growing steers. Diets contained 77% sorghum grain either DR or SF at densities of 437, 360, and 283 g/L (SF34, SF28, and SF22, respectively). Eight crossbred steers (340 kg initial BW), implanted with indwelling catheters into portal, hepatic, and mesenteric veins and the mesenteric artery, were used in a randomized complete block design. Blood flows and net output or uptake of ammonia N, urea N (UN), and alpha-amino N (AAN) were measured across portal-drained viscera, hepatic, and splanchnic tissues. Plasma arterial, portal, and hepatic concentrations of individual amino acids were also measured. Decreasing FD linearly increased (P = .04) net absorption of AAN (51, 73, and 78 g/d for SF34, SF28, and SF22, respectively) and transfer (cycling) of blood UN to the gut (49, 48 and 64 g/d; P = .02). Net UN cycling averaged 38% of N intake across all diets. Hepatic uptake of AAN or UN synthesis, and splanchnic output of AAN and UN, were not altered by FD. Lowering FD linearly increased (P < or = .02) portal-arterial concentration differences for blood AAN and UN and plasma arterial concentrations for alanine. Steers fed SF compared to DR tended to have greater (P = .11) blood UN cycling (percentage of hepatic synthesis; 64 vs 50%) and decreased (P = .03) net splanchnic UN output (30 vs 50 g/d), but other net fluxes of N were not altered across splanchnic tissues. Steam-flaking compared to dry-rolling tended to decrease (P = .12) portal, but not hepatic, blood flow and increased (P < .01) hepatic-arterial concentration differences for blood UN. Except for a decrease (P = .01) in hepatic-arterial concentration differences of glutamine, plasma amino acid concentrations were not altered by feeding SF vs DR sorghum. Processing method (steam-flaking vs dry-rolling) or increasing the degree of processing (by decreasing FD) of SF sorghum grain resulted in greater transfer of blood UN to the gut. Reducing FD also linearly increased the absorption of AAN by growing steers, which explains (in part) published responses of superior performance by steers fed SF grains.

Influence of grain processing in regard to serum metabolites and enzymes for finishing bull calves

“…The time course of the interaction is puzzling although note that in most of the data, PF calves had higher SUN concentration than GF calves. This finding shows that, effectively, grain processing seems to affect the recycling of urea, increasing the supply of high-quality microbial protein for absorption, as was described for growing beef steers by Alio et al (2000) and Theurer et al (2002), and in accordance with the productive results found in the study of Suárez (2009).…”

Ammonia production, ammonia absorption, and urea recycling in ruminants. A review

“…Liver metabolism has a central role in the integration of body N metabolism. Ammonia in the liver is detoxifi ed by conversion to urea, urea can then be recycled directly into the rumen, small intestine, or large intestine; it can enter the rumen in saliva, be excreted by the kidney, or be secreted in milk or sweat (Alio et al, 2000).…”

Processamento de milho (floculado vs. laminado a vapor) e adição de monensina para bezerras leiteiras, pré e pós-desmama precoce

“…Em trabalho subsequente, avaliando desempenho de bezerros da desmama aos 120 dias, estes autores também não observaram efeito devido a diferentes densidades de processamento de milho. Embora a melhor densidade de grão floculado esteja determinada para vacas em lactação (360 g/L) (Theurer, 1999) e para animais de corte em confinamento (280 g /L) (Alio et al, 2000), este valor ainda não está estabelecido para bezerros em aleitamento ou após a desmama.…”