|Taylor, Joshua - Bret|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2008
Publication Date: 4/1/2008
Citation: Ward, M.A., Neville, T.L., Reed, J.J., Taylor, J.B., Hallford, D.M., Soto-Navarro, S.A., Vonnahme, K.A., Redmer, D.S., Reynolds, L.P., Caton, J.S. 2008. Effects of selenium supply and dietary restriction on maternal and fetal metabolic hormones in pregnant ewe lambs. Journal of Animal Science. 86:1254-1262. Interpretive Summary: Selenium is an essential micronutrient that supports many important functions in pregnant mammals. Although selenium is most noted for its role in antioxidant protein function, it is also a key component of protein enzymes required for thyroid hormone activity. Thyroid hormones (T3 and T4), as well as hormones such as insulin-like growth factor-I (IGF-1), play important roles in fetal development and energy metabolism in pregnant sheep. Because of severe climatic conditions, pregnant sheep grazing western ranges during the winter may experience periods of limited nutrition. Furthermore, depending upon geographical location, selenium may also be limiting. Our primary objectives were to investigate the impacts of 1) restricted nutrition and 2) supplemental selenium on pregnant adolescent sheep and their fetuses. When dietary protein and energy were restricted during pregnancy, IGF-1 decreased in the serum of the ewe and fetus, thyroid hormones decreased in the serum of the ewe, and the ratio of T4:T3 increased in the serum of the ewe. However, when supranutritional levels of organically-bound selenium were included in the energy and protein-restricted diets, the ratio of T4:T3 was restored to the ratio observed in pregnant ewes that were fed adequate protein and energy. Therefore, pregnant adolescent ewes experiencing periods of limited nutrition may benefit from supranutritional organically-bound selenium.
Technical Abstract: Objectives were to evaluate effects of dietary restriction and Se on maternal and fetal metabolic hormones. In Exp. 1, pregnant ewe lambs (n = 32; initial BW = 45.6 ± 2.3 kg) were allotted randomly to 1 of 4 treatments. Diets contained (DM basis) either no added Se (control), or supranutritional Se added as high-Se wheat at 3.0 ppm (Se-wheat), or sodium selenate at 3 (Se3) and 15 (Se15) ppm Se. Diets (DM basis) were similar in CP (15.5%) and ME (2.68 Mcal/kg). Treatments were initiated at 50 ± 5 d of gestation. The control, Se-wheat, Se3, and Se15 treatments provided 2.5, 75, 75, and 375 ug/kg BW of Se, respectively. Ewe jugular blood samples were collected at 50, 64, 78, 92, 106, 120, and 134 d of gestation. Fetal serum samples were collected at necropsy on d 134. In Exp. 2, pregnant ewe lambs (n = 36; initial BW 53.8 ± 1.3 kg) were allotted randomly to treatments in a 2 x 2 factorial arrangement. Factors were nutrition (control, 100% of requirements vs. restricted nutrition, 60% of controls) and dietary Se (adequate Se; 6 ug/kg BW vs. high Se; 80 ug/kg BW). Selenium treatments were initiated 21 d before breeding, and nutritional treatments on d 64 of gestation. Diets were 16% CP and 2.12 Mcal/kg of ME (DM basis). Ewe blood samples were collected at 62, 76, 90, 104, 118, 132, and 135 d of gestation. Fetal blood was collected at necropsy on d 135. In Exp.1, dietary Se source and level had no effect (P > 0.17) on maternal and fetal serum IGF-I, triiodothyronine (T3), and thyroxine (T4) concentrations. Selenium supplementation increased (P = 0.06) the T4:T3 ratio vs. controls. In Exp. 2, dietary Se had no impact (P > 0.33) on main effect means for maternal and fetal serum IGF-I, T3, and T4 concentrations measured from d 62 to 132 ; however, high Se ewes had lower (P = 0.01) serum T4 levels at d 135 than adequate Se ewes. A nutrition by Se interaction (P = 0.06) was detected in T4:T3 ratios; ewes fed restricted and adequate Se diets had greater (P = 0.10) T4:T3 ratios than other treatments. Nutrient-restricted ewes had lower (P < 0.05) serum IGF-I, T3, and T4 concentrations. Fetal serum IGF-I concentrations were lower (P = 0.01) in restricted vs. control fed ewes; however, fetal T3 and T4 concentrations were unaffected (P > 0.13) by dietary Se or maternal plane of nutrition. These data indicate that dietary Se may alter maternal T4:T3 ratios. Nutrient restriction during gestation reduces maternal IGF-I, T3, and T4 and fetal IGF-I concentrations.