Influence of slow-release urea on nitrogen balance and portal-drained visceral nutrient flux in beef steers

Abstract

Two experiments were conducted to evaluate the effects of slow-release urea (SRU) versus feed-grade urea on portal-drained visceral (PDV) nutrient flux, nutrient digestibility, and total N balance in beef steers. Multi-catheterized steers were used to determine effects of intraruminal dosing (Exp. 1; n = 4; 319 +/- 5 kg of BW) or feeding (Exp. 2; n = 10; 4 Holstein steers 236 +/- 43 kg of BW and 6 Angus steers 367 +/- 46 kg of BW) SRU or urea on PDV nutrient flux and blood variables for 10 h after dosing. Intraruminal dosing of SRU (Exp. 1) prevented the rapid increase in ruminal ammonia concentrations that occurred with urea dosing (treatment x time P = 0.001). Although apparent total tract digestibilities of DM, OM, NDF, and ADF were not affected by treatment (P > 0.53, Exp. 2), SRU increased fecal N excretion (49.6 vs. 45.6 g/d; P = 0.04) and reduced apparent total tract N digestibility (61.7 vs. 66.0%; P = 0.003). Transfer of urea from the blood to the gastrointestinal tract occurred for both treatments in Exp. 1 and 2 at all time points with the exception for 0.5 h after dosing of urea in Exp. 1, when urea was actually transferred from the gastrointestinal tract to the blood. In both Exp. 1 and 2, both urea and SRU treatments increased arterial urea concentrations from 0.5 to 6 h after feeding, but arterial urea concentrations were consistently less with SRU (treatment x time P < 0.001, Exp. 1; P = 0.007, Exp. 2). Net portal ammonia release remained relatively consistent across the entire sampling period with SRU treatment, whereas urea treatment increased portal ammonia release in Exp. 1 and tended to have a similar effect in Exp. 2 (treatment x time P = 0.003 and P = 0.11, respectively). Urea treatment also increased hepatic ammonia uptake within 0.5 h (treatment x time P = 0.02, Exp. 1); however, increased total splanchnic release of ammonia for the 2 h after urea treatment dosing suggests that PDV ammonia flux may have exceeded hepatic capacity for removal. Slow-release urea reduces the rapidity of ammonia-N release and may reduce shifts in N metabolism associated with disposal of ammonia. However, SRU increased fecal N excretion and increased urea transfer to the gastrointestinal tract, possibly by reduced SRU hydrolysis or effects on digestion patterns. Despite this, the ability of SRU to protect against the negative effects of urea feeding may be efficacious in some feeding applications.

Effect of diets differing in rumen soluble nitrogen on utilization of poor-quality roughage by sheep

“…In contrast with the present findings (Table 4), Ribeiro et al (2011) found no differences in N digestibility between urea and Optigen® II treatments. According to the findings of this study, it could be suggested that post-ruminal N concentration would increase when Optigen® II is used to replace urea completely in a supplement, and therefore increased faecal N levels could be expected (Taylor-Edwards et al, 2009a). …”

Utilização de ureia encapsulada de liberação lenta na alimentação de vacas em lactação

“…(TAYLOR-EDWARDS et al, 2009). Estes compostos não têm sido tão vantajosos como a ureia, pois uma parte substancial do NNP neles presente pode não ser convertida em NH 3 pelo rúmen, reduzindo a sua incorporação à proteína microbiana (GALO et al, 2003;FIRKINS et al, 2007).…”

“…Não foram encontradas diferenças no pH, na produção total e proporção molar dos ácidos graxos voláteis. (HUNTINGTON et al, 2006;GOLOMESKI et al, 2006;TAYLOR-EDWARDS et al, 2009;HIGHSTREET et al, 2010;INOSTROZA et al, 2010;PINOS-RODRÍGUEZ et al, 2010;XIN et al, 2010). No entanto, as concentrações de N-NH 3 nos tratamento com ureia de liberação lenta e com proteína isolada de soja continuou declinando.…”

Substituição do farelo de soja por fontes de nitrogênio não-protéico em bovinos Nelore

“…Os compostos de uréia de liberação lenta que tem sido utilizados em dieta de ruminantes incluem biureto, amiréia, uréia fosfato e uréia com revestimentos a base de óleos, formaldeído e polímeros (Taylor-Edwards et al, 2009).…”

“…A utilização de uréia de liberação lenta in vivo apresenta uma taxa mais lenta de liberação de nitrogênio amoniacal do que a uréia e pode efetivamente modular as concentrações de nitrogênio amoniacal quando substituído por uréia (Huntington et al, 2006;Golomeski et al, 2006;Taylor-Edwards et al, 2009;Cherdthong et al, 2010;Highstreet et al, 2010;Inostroza et al, 2010;Pinos-Rodríguez et al, 2010;Xin et al, 2010).…”