The objectives were to determine the effects of forage level and grain processing on whole-body urea kinetics, N balance, serosal-to-mucosal urea flux (Jsm-urea), and messenger ribonucleic acid (mRNA) abundance of urea transporter-B (UT-B; SLC14a1) and aquaporins (AQP) in ovine ruminal, duodenal, and cecal epithelia. Thirty-two wether lambs were blocked by body weight into groups of four and assigned to one of four diets (n = 8) in a 2 × 2 factorial design. Dietary factors were forage level (30% [LF] vs. 70% [HF]) and corn grain processing (whole-shelled [WS] vs. steam-flaked [SF]). Four blocks of lambs (n = 4) were used to determine urea kinetics and N balance using 4-d [15N15N]-urea infusions with concurrent fecal and urine collections. Lambs were killed after 23 d of dietary adaptation. Ruminal, duodenal, and cecal epithelia were collected to determine Jsm-urea and mRNA abundance of UT-B and AQP. Lambs fed LF had greater intakes of dry matter (DMI; 1.20 vs. 0.86 kg/d) and N (NI; 20.1 vs. 15.0 g/d) than those fed HF (P < 0.01). Lambs fed SF had greater DMI (1.20 vs. 0.86 kg/d) and NI (20.6 vs. 14.5 g/d) than those fed WS (P < 0.01). As a percentage of NI, total N excretion was greater in lambs fed HF compared with those fed LF (103% vs. 63.0%; P < 0.01) and was also greater in lambs fed WS compared with those fed SF (93.6% vs. 72.1%; P = 0.02). Retained N (% of NI) was greater in lambs fed LF compared with those fed HF (37.0% vs. -2.55%; P < 0.01). Lambs fed SF had a greater (P = 0.02) retained N (% of NI; 28.0% vs. 6.50%) compared with those fed WS. Endogenous urea production (UER) tended (P = 0.09) to be greater in lambs fed HF compared with those fed LF. As a proportion of UER, lambs fed HF had a greater urinary urea-N loss (0.38 vs. 0.22) and lower urea-N transferred to the gastrointestinal tract (GIT; 0.62 vs. 0.78) or urea-N used for anabolism (as a proportion of urea-N transferred to the GIT; 0.12 vs. 0.26) compared with lambs fed LF (P < 0.01). Ruminal Jsm-urea was unaffected by diet. Duodenal Jsm-urea was greater (P < 0.01) in lambs fed HF compared with LF (77.5 vs. 57.2 nmol/[cm2 × h]). Lambs fed LF had greater (P = 0.03) mRNA expression of AQP3 in ruminal epithelia and tended (P = 0.06) to have greater mRNA expression of AQP3 in duodenal epithelia compared with lambs fed HF. Expression of UT-B mRNA was unaffected by diet. Our results showed that feeding more ruminally available energy improved N utilization, partly through a greater proportion of UER being transferred to the GIT and being used for anabolic purposes.

中文翻译：

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饲草水平和玉米粒加工对绵羊瘤胃，十二指肠和盲肠上皮中全身尿素动力学，浆膜到粘膜尿素通量以及尿素转运蛋白和水通道蛋白表达的影响。

目的是确定饲草水平和谷物加工对全身尿素动力学，氮平衡，浆膜至粘膜尿素通量（Jsm-urea）和信使核糖核酸（mRNA）尿素转运蛋白B（ UT-B; SLC14a1）和绵羊瘤胃，十二指肠和盲肠上皮中的水通道蛋白（AQP）。将三十二只羔羊羔按体重分成四组，并按2×2因子设计分配给四种饮食之一（n = 8）。饮食因素是草料水平（30％[LF]相对70％[HF]）和玉米谷物加工（全壳[WS]相对于蒸汽压片[SF]）。使用4-d [15N15N]-尿素输注并同时收集粪便和尿液，使用四块羊羔（n = 4）确定尿素动力学和氮平衡。饮食适应23天后，羔羊被杀死。瘤，十二指肠，收集盲肠上皮和盲肠上皮，测定UT-B和AQP的Jsm-尿素和mRNA丰度。饲喂LF的羔羊的干物质摄入量（DMI； 1.20 vs. 0.86 kg / d）和N（NI； 20.1 vs. 15.0 g / d）比饲喂HF的羔羊更多（P <0.01）。饲喂SF的羔羊的DMI（1.20 vs. 0.86 kg / d）和NI（20.6 vs. 14.5 g / d）比饲喂WS的羔羊更高（P <0.01）。饲喂HF的羔羊的总N排泄量比饲喂LF的羔羊高（103％vs. 63.0％； P <0.01），而饲喂WS的羔羊的总氮排泄比SF饲喂的更高（93.6％vs. 6％）。 72.1％； P = 0.02）。饲喂LF的羔羊比饲喂HF的羔羊的保留氮（占NI的百分比）更高（37.0％vs -2.55％； P <0.01）。与饲喂WS的羔羊相比，饲喂SF的羔羊保留的N更大（P = 0.02）（占NI的百分比； 28.0％比6.50％）。内源尿素生产（UER）趋于（P = 0。09）饲喂HF的羔羊比饲喂LF的羔羊更大。饲喂HF的羔羊占URER的比例较高，尿尿素氮损失较大（0.38对0.22），转移到胃肠道的尿素氮（GIT； 0.62对0.78）或尿素氮用于合成代谢（如与饲喂LF的羔羊相比，转移到GIT中的尿素N的比例为0.12比0.26）（P <0.01）。瘤胃Jsm-尿素不受饮食影响。饲喂HF的羔羊与LF相比，十二指肠Jsm-尿素更大（P <0.01）（77.5 vs. 57.2 nmol / [cm2×h]）。饲喂LF的羔羊与饲喂HF的羔羊相比，瘤胃上皮中的AQP3 mRNA表达更高（P = 0.03），并且趋于（P = 0.06）在十二指肠上皮中的AQP3 mRNA表达更高。饮食不影响UT-B mRNA的表达。我们的结果表明，饲喂更多反刍动物可利用的能量可以提高氮的利用率，