Effects of selenium supply and dietary restriction on maternal and fetal metabolic hormones in pregnant ewe lambs

¹ Center for Nutrition and Pregnancy, Animal and Range Sciences Department, North Dakota State University, Fargo 58105
² USDA-ARS, US Sheep Experiment Station, Dubois, ID 83423
³ Animal and Range Sciences Department, New Mexico State University, Las Cruces 88003

^* To whom correspondence should be addressed. E-mail: Joel.Caton{at}ndsu.edu.

	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; 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 µg/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; 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 µg/kg BW vs. high Se, 80 µg/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 concentration 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, at d 135, high Se ewes had less (P = 0.01) serum T₄ concentrations 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 less (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.

Key Words: ewes, fetus, metabolic hormones, pregnancy, selenium