|Taylor, Joshua - Bret|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/21/2009
Publication Date: 3/1/2010
Citation: Lekatz, L.A., Caton, J.S., Taylor, J.B., Reynolds, L.P., Redmer, D.A., Vonnahme, K.A. 2010. Maternal selenium supplementation and timing of nutrient restriction in pregnant sheep: Effects on maternal endocrine status and placental characteristics. Journal of Animal Science. 88:955-971. Interpretive Summary: Some rangelands in the western United States can be challenging to utilize for livestock production. For example, some areas of the Intermountain West are deficient in the mineral selenium. Furthermore, forage growth on western ranges can be minimal during drought, which results in limited or insufficient nutrition for grazing animals, especially pregnant animals. Because these ranges are extensive, remote, and rugged, providing supplemental nutrition to grazing livestock is often prohibitive or very costly. Scientists at the USSES and North Dakota State University, Fargo, have considered these production challenges extensively. Using a creative experimental approach, they studied how limited nutrition and high levels of dietary selenium during pregnancy affect growth of adolescent ewe lambs and their fetus. The results show that both the fetus and the placenta seem to adapt to nutrient restriction during mid- to late pregnancy. Furthermore, feeding diets rich in organically-bound selenium during mid- to late pregnancy “loads” the ewe and fetus with selenium, which will enable the ewe and offspring to graze selenium-deficient ranges without the need for selenium supplement.
Technical Abstract: The objective was to determine the effects of dietary selenium and nutrient restriction (level and timing) on serum hormone and metabolite levels and placental characteristics in mid- to late-pregnancy ewes. Pregnant ewe lambs (n = 64) were assigned to 1 of 8 treatments arranged in a 2 x 2 x 2 factorial array: Se level (initiated at breeding; adequate [3.05 mcg/kg BW] or high [70.4 mcg/kg BW]) and nutritional level (100% [control] or 60% [restricted] of NRC recommendations) that was altered at different periods of pregnancy (d 50 to 90 [mid] or d 91 to 130 [late]). Nutrient-control ewes had a greater (P = 0.01) change in body weight than nutrient-restricted ewes during both mid- and late pregnancy. Serum urea N was not affected by diet; however, nutrient-restricted ewes had greater (P = 0.01) serum levels of nonesterified fatty acids on d 66, 78, 106, 120, and 130 of pregnancy compared with nutrient-control ewes. Both dietary selenium and timing of nutrient restriction altered serum progesterone concentrations and nutrient restriction altered serum thyroxine and triiodothyronine concentrations in the dam. Nutrient restriction during late pregnancy decreased (P = 0.01) fetal body and fluid weights compared with no nutrient restriction (control). Cotyledonary cellular proliferation was decreased (P < 0.05) in high-Se-fed compared with adequate-Se-fed ewes. Nutrient restriction affected vascular endothelial growth factor (VEGF) receptor, placental growth factor, and endothelial nitric oxide synthase mRNA abundance in caruncular tissue. Nutrient restriction affected VEGF, VEGF receptors, and endothelial nitric oxide synthase mRNA abundance in the cotyledonary tissue. These results indicate that level of dietary selenium and duration and timing of nutrient restriction during pregnancy altered placental nutrient transport and function in pregnant ewes. Whether these alterations positively or negatively affect the fetus was not determine and is the subject of ongoing research.