|Taylor, Joshua - Bret|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/18/2010
Publication Date: 11/1/2010
Publication URL: http://jas.fass.org/content/88/11/3645
Citation: Neville, T.L., Caton, J.S., Hammer, C.J., Reed, J.J., Luther, J.S., Taylor, J.B., Vonnahme, K.A. 2010. Ovine offspring growth and diet digestibility are influenced by maternal Se supplementation and nutritional intake level during pregnancy despite a common postnatal diet. Journal of Animal Science. 88:3645-3656. Interpretive Summary: Marginal selenium deficiency can result in a 33% loss in annual revenue from a ewe flock. Frequent supplementation of selenium is necessary for sheep produced in selenium-deficient regions. Unfortunately, the extensiveness and ruggedness of Intermountain West rangelands often prohibits frequent access to grazing sheep. Therefore, a low-frequency supplement strategy is needed that enhances long-term selenium status of grazing sheep. Through use of selenomethionine-rich feed sources, we have developed such a strategy. However, the strategy requires that selenium must be fed at 10- to 20-fold the daily requirement. Because of inaccurate generalizations about selenium toxicity (e.g., NRC, Nutrient Requirements of Sheep, 1985), many are concerned that providing selenium at this level of intake may be unsafe for livestock. Therefore, we report on the effects of feeding selenium at 20- to 100-fold the daily requirement to ewes during that last 90 days of pregnancy. Selenium fed at 100-fold the daily requirement altered some markers of vascular growth the intestines of the ewes and fetuses. However, no effect was observed when selenium was fed at 20-fold the daily requirement. Overall, no general symptoms of selenium toxicity were observed. We conclude that it is safe to feed pregnant ewes selenium, from selenomethionine-rich feeds, up to 20-fold the daily requirement.
Technical Abstract: Objectives were to evaluate effects of maternal dietary restriction and Se supply on angiogenic factor mRNA expression in intestinal and mammary tissues, and jejunal crypt cell proliferation and vascularity in late term fetal intestines. In Exp. 1, pregnant ewe lambs (n = 32; initial BW = 45.6 +/- 2.3 kg) were allotted randomly to 1 of 4 treatments. Treatments (initiated d 50 +/- 5 d gestation) were: control (3.5 ug of Se/kg of BW/d), Se-wheat (75 ug of Se/kg of BW/d), selenate (Se3; providing 75 ug of Se/kg of BW/d), selenate (Se15 providing 375 ug of Se/kg of BW/d). Diets (DM basis) were similar in CP (15.5%) and ME (2.68 Mcal/kg). 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 array. Factors were nutrition (control, 100% of requirements vs. restricted nutrition, 60% of controls) and dietary Se (adequate Se; 6 ug of Se/kg of BW/d vs. high Se; 80 ug of Se/kg of BW/d). Selenium treatments were initiated 21 d before breeding, and nutritional treatments on d 64 of gestation. Diets (DM basis) were 16% CP and 2.12 Mcal/kg of ME. In Exp. 1, Se15 increased (P = 0.07) vascular endothelial growth factor (VEGF) mRNA expression, while Se supplementation decreased (P = 0.06) kinase insert domain receptor (KDR) mRNA in maternal mucosal scrape on d 134 of gestation. Expression of VEGF mRNA was decreased by Se (P = 0.10) in fetal jejunum. In mammary tissue, fms-related tyrosine kinase 1 (FLT1) and KDR mRNA were greater in Se-wheat compared with Se3 and KDR expression was increased (P = 0.10) in Se15 compared with Se3. In Exp. 2, dietary restriction increased (P < 0.07) expression of mRNA for VEGF, FLT1, KDR, neuropilin (NRP)-1, NRP-2, and hypoxia-inducible factor 1, alpha subunit (HIF1A) in mucosal scrapes from maternal jejunum. In fetal jejunum, soluble guanylate cyclase (GUCY1B3), was decreased (P = 0.01) by maternal dietary restriction from d 64 to 135 of gestation. Total microvascularity in fetal jejunum was reduced (P = 0.002) by maternal dietary restriction. Mammary gland expression of VEGF, NRP1, ANGPT receptor (TEK), and endothelial nitric oxide synthase 3 (NOS3), increased (P < 0.09) while angiopoietin (ANGPT)-1 decreased (P = 0.05) due to nutrient restriction. Data indicate that expression of angiogenic factors and receptors in maternal intestine, mammary gland, and fetal jejunum are responsive to maternal nutrition and likely explain observed changes in tissue vascularity.