Davis P A, McDowell L R, Wilkinson N S, Buergelt C D, Van Alstyne R, Weldon R N, Marshall T T
Department of Animal Sciences, University of Florida, Gainesville, 32611, USA.
J Anim Sci. 2006 Mar;84(3):660-8. doi: 10.2527/2006.843660x.
The objectives of this 72-wk study were to evaluate and compare the effects of 6 dietary levels of inorganic Se on serum, whole blood, wool, and tissue Se concentrations and to determine the maximum tolerable level of Se for mature ewes during lamb production. Forty-one, 4-yr-old, range-type ewes (57.4 +/- 5.7 kg) were used in a completely randomized design with 6 dietary treatments. Sodium selenite was added to a corn and soybean meal-based diet to provide 0.2 (control), 4, 8, 12, 16, or 20 mg of dietary Se/kg to ewes during lamb production. Serum Se and ewe BW were measured at 4-wk intervals; whole blood Se and wool Se were measured every 12 wk; and samples of brain, diaphragm, heart, hoof, kidney, liver, and psoas major were collected at the termination of the experiment. Dietary Se did not affect ewe BW during the study (P = 0.69), and there was no treatment x time interaction. Serum Se increased linearly as dietary Se level increased (P < 0.001) and responded cubically (P = 0.02) over time. Selenium in whole blood increased linearly (P < 0.001) as supplemental Se increased. Wool Se increased linearly (P < 0.001) as dietary Se increased, and the response over time was quadratic (P < 0.001). Brain, diaphragm, heart, and psoas major Se increased (P < 0.05) linearly as dietary Se increased, liver Se responded quadratically (P < 0.05), and hoof and kidney Se increased cubicically (P < 0.05) as supplemental Se increased. In general, serum, whole blood, and tissue Se concentrations of ewes receiving 12, 16, or 20 mg of dietary Se/kg were greater (P < 0.05) than those of controls and ewes receiving less dietary Se. Although they were elevated in ewes receiving increased dietary Se, at no time did serum, whole blood, or wool Se concentrations reach levels previously reported as toxic, nor were clinical signs of Se toxicosis observed. Histopathological evaluation of liver, kidney, diaphragm, heart, and psoas major did not reveal evidence of Se toxicosis in ewes at any dietary Se level. Ewes under our experimental conditions and during the stresses of production were able to tolerate up to 20 mg of dietary Se/kg as sodium selenite for 72 wk. These findings suggest that the maximum tolerable level of inorganic Se for sheep is much greater than 2 mg/kg as was suggested previously. Experiments of longer duration and utilizing greater dietary Se concentrations are necessary to clearly define the maximum tolerable level.
这项为期72周的研究旨在评估和比较6种无机硒日粮水平对血清、全血、羊毛和组织中硒浓度的影响，并确定成年母羊在产羔期间的最大耐受硒水平。选用41只4岁、体型中等的母羊（体重57.4±5.7千克），采用完全随机设计，设置6种日粮处理。在产羔期间，向以玉米和豆粕为基础的日粮中添加亚硒酸钠，使母羊的日粮硒含量分别达到0.2（对照）、4、8、12、16或20毫克/千克。每隔4周测量血清硒和母羊体重；每12周测量全血硒和羊毛硒；实验结束时采集脑、膈肌、心脏、蹄、肾脏、肝脏和腰大肌样本。研究期间，日粮硒对母羊体重没有影响（P = 0.69），也不存在处理×时间交互作用。血清硒随着日粮硒水平的升高呈线性增加（P < 0.001），且随时间呈三次方响应（P = 0.02）。随着添加硒量的增加，全血中的硒呈线性增加（P < 0.001）。随着日粮硒含量的增加，羊毛硒呈线性增加（P < 0.001），且随时间的响应呈二次方（P < 0.001）。随着日粮硒含量的增加，脑、膈肌、心脏和腰大肌中的硒呈线性增加（P < 0.05），肝脏硒呈二次方响应（P < 0.05），蹄和肾脏中的硒呈三次方增加（P < 0.05）。一般来说，日粮硒含量为12、16或20毫克/千克的母羊血清、全血和组织中的硒浓度高于对照组和日粮硒含量较低的母羊（P < 0.05）。尽管日粮硒增加的母羊中这些指标有所升高，但血清、全血或羊毛硒浓度从未达到先前报道的中毒水平，也未观察到硒中毒的临床症状。对肝脏、肾脏、膈肌、心脏和腰大肌的组织病理学评估未发现任何日粮硒水平下母羊存在硒中毒的迹象。在我们的实验条件下以及生产应激期间，母羊能够耐受高达20毫克/千克亚硒酸钠的日粮硒长达72周。这些发现表明，绵羊对无机硒的最大耐受水平远高于先前建议的2毫克/千克。需要进行更长时间和更高日粮硒浓度的实验，以明确最大耐受水平。
