Impact of Selenium Supplementation on Ovine Colostrum Bioactives and Postnatal Health

Lambing mortality rates over 10% have been identified as detrimental to sheep producer profitability, yet global lamb mortality rates have consistently been reported between 15-20% over the past four decades. An important aspect of ewe health that contributes to colostrum quality and offspring health is maternal nutrient status. Selenium (Se) is an essential trace mineral vital to ruminant health and productivity, and Se deficiencies in sheep can lead to failure of passive transfer and immunocompromised lambs. Se-deficient soils can be found globally, and therefore poor Se status in ewes may contribute to higher lamb mortalities. While inorganic Se supplementation is less costly, organic Se supplementation offers more bioavailable Se, and may be a more proficient method of ensuring ewes and lambs receive adequate Se. The objective of this thesis was to evaluate the effects of maternal Se supplementation on the maternal gut microbiome, colostrum composition, and lamb Se status, immuno-robustness, biomarker status, intestinal development, and hepatic gene expression. In a randomized complete block design, Dorset-Rideau ewes were enrolled in a feeding trial starting on gestation day 110 and ending on postpartum day 52. All ewes were fed a Se-deficient diet and supplemented with either no Se, 0.3 mg/day inorganic Se, 0.3 or 0.6 mg/day organic Se via oral gavage. Ewe gut microbiome composition, colostrum composition, lamb Se status, lamb biomarker profiles, lamb intestinal morphology, and lamb hepatic gene expression were assessed between postpartum days 0 and 52. Results demonstrated that the ewe gut microbiome, colostrum composition, lamb Se status, and lamb biomarker status were significantly impacted by organic Se supplementation as compared to the control group and inorganic Se supplementation. Many responses observed to organic Se supplementation proved to be nonlinear, indicating an individual response to each level of organic Se. Overall, this work has demonstrated that maternal organic Se supplementation improved Se status in colostrum and lambs, as well as altered the ewe gut microbiome and offered greater benefits to lamb health. The work in this thesis has also contributed to the pool of knowledge regarding organic Se and has identified areas where more research is needed.