Effect of selenium source and supplementation rate in ewes on selenium status, passive immunity and growth performance of their lambs Public Deposited

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  • Selenium (Se) is an essential micronutrient of sheep. Supplementation is especially important in young lambs in order to prevent Se-deficiency signs. In the United States, the FDA regulates Se supplementation to ruminant diets at a level of 0.3 mg/kg Se (as fed basis). Questions still exist regarding what chemical form of Se is the most bioavailable supplement and what are the best supplementation rates for optimal productivity. Three interrelated experiments from the same study were conducted 1) to evaluate the effect of Se source and supplementation rate in ewes on Se status of their lambs at birth, 2) to examine the effect of Se source and supplementation rate on IgG concentrations in ewe colostrum and lamb serum, and 3) to evaluate the effects of Se source and supplementation rate on ewe reproductive performance and subsequent vitality and growth performance of their lambs. For these experiments, 240 ewes were divided into 8 treatment groups and drenched weekly (at an amount equal to their summed daily intake) for one year, including during gestation and early lactation, with no Se (deficient); at recommended levels (0.3 mg/kg) with inorganic sodium selenite, sodium selenate, or organic Se-yeast (Se-Y); or at supranutritional levels (0.9 and 1.5 mg/kg) with sodium selenite or Se yeast. In the third experiment, 88 ewes continued the study into year two for an additional 28 weeks. Year two treatments included no Se (deficient) ewes (n = 25); ewes supplemented at recommended levels (0.3 mg/kg) with organic Se-Y (n = 20); ewes supplemented at supranutritional levels (0.9 and 1.5 mg/kg) with organic Se-Y (n = 18 and 27, respectively). In the first experiment, which assessed the effects of Se source and supplementation rate in ewes on Se status of their offspring, we found that Se administered by weekly drenching of ewes during gestation and early lactation was effective at increasing Se concentrations in ewe colostrum and milk at 30 days in milk (DIM), and in improving the Se status of lambs (whole-blood and serum Se at birth, and skeletal-muscle Se at 14 days of age) (all P < 0.001). Selenium concentrations in lacteal secretions and lambs were higher in ewes drenched with Se yeast compared to ewes drenched with inorganic Se sources (P < 0.01). Selenium concentrations in lacteal secretions and in lambs increased linearly with supranutritional concentrations of Se yeast (P < 0.001), whereas Se concentrations did not differ in ewes drenched with 0.9 or 1.5 mg/kg of inorganic sodium selenite (P > 0.05). In summary, weekly oral drenching of ewes with Se yeast during gestation and early lactation was found to be an effective method for improving Se status of their newborn lambs. In the second experiment, which examined the effects of Se source and supplementation rate in ewes on colostral IgG and lamb serum-IgG concentrations, we measured colostral and lamb serum-IgG concentrations at parturition, and lamb serum-IgG concentration again at 48 hours postnatal. Although Se drenching of ewes was effective at increasing whole-blood Se concentrations in ewes and lambs (P < 0.001), and colostral Se concentration (P < 0.001), there was no consistent or significant increase in IgG concentrations in ewe colostrum nor lamb serum at 48 hours of age (P > 0.05) irrespective of Se source, or supplementation rate. Therefore, we conclude that Se supplementation in ewes, and the Se status of newborn lambs, have little effect on IgG concentrations in colostrum and subsequent IgG concentrations in lamb serum at 48 hours postnatal. The purpose of the third experiment was to examine the effect of Se source and supplementation rate on ewe reproductive performance and subsequent vitality and growth performance of lambs, over two consecutive lambing seasons. In year one, lambing percent; number of lambs born per ewe; lamb birth weights; 90- and 120-day BW and ADG; and pounds of lamb weaned per ewe were measured. The purpose of the second year of this study was to continue our observations for the SeY treated ewes, adding additional parameters to monitor ewe reproductive performance (percentage of ewes exhibiting estrus; percentage of ewes exhibiting estrus that lambed; percentage of ewes lambing; and number of lambs born per ewe). Year two lamb performance measures included birth weights; neonatal vigor scores; 10-, 20-, and 60-day BW and ADG; and percentage of lambs surviving to 60 days. In year one, Se supplementation, regardless of supplementation rate, did not affect lambing percent, number of lambs born per ewe, lamb birth weights, 90-day BW and ADG, or pounds of lamb weaned per ewe. However, lambs from ewes in the 1.5 mg/kg SeY group had greater120-day BW (P = 0.10) and ADG (P = 0.06) than lambs from ewes in the 0.3 mg/kg group. This same trend was apparent in a subgroup of lambs from Suffolk ewes receiving Se at 1.5 mg/kg that had greater 120-day BW (P = 0.07) and ADG (P = 0.09) compared to lambs receiving SeY at 0.3 mg/kg. Similarly, a subgroup of lambs reared as twins from ewes receiving Se at 1.5 mg/kg had greater120-day BW (P = 0.07) and ADG (P = 0.08) than lambs reared as twins from ewes in the 0.3 mg/kg group. In year two, there were two ewe reproductive performance measures that were negatively affected by Se supplementation. First, the percentage of ewes exhibiting estrus that lambed in the 0.3 mg/kg SeY group (75%) was lower compared to ewes receiving no Se supplement (100%; P = 0.02). Also, the percentage of ewes lambing was lower (P< 0.04) for ewes receiving 0.3 mg/kg SeY (75%) compared to ewes receiving no Se supplemental (96%). Se supplementation, regardless of source and supplementation rate did not affect percentage of ewes exhibiting estrus, or number of lambs born per ewe. There were three lamb performance measures that were affected by Se supplementation. Lambs from ewes receiving Se at 1.5 mg/kg tended to have greater lamb vigor scores compared to lambs from ewes receiving SeY at 0.3 mg/kg (P = 0.07). Second, the 60-day ADG was greater for lambs from ewes in the 1.5 mg/kg group compared to lambs from ewes in the no Se group (P =0.07). A subgroup of lambs from Suffolk ewes receiving Se at 1.5 mg/kg had greater 60-day BW (P = 0.03) and ADG (P = 0.06) compared to lambs receiving SeY at 0.3 mg/kg. Similarly, a subgroup of lambs reared as twins from ewes receiving Se at 1.5 mg/kg had greater 60-day BW (P = 0.08) and ADG (P = 0.06) than lambs reared as twins from ewes in the 0.3 mg/kg group. Third, there was an increased percentage of lambs surviving to 60 days in lambs from ewes in the 1.5 mg/kg group compared to lambs from ewes in the no Se group (86% vs. 64%, respectively; P =0.04). Se supplementation, regardless of source and supplementation rate, did not affect lamb birth weight nor 10- and 20-day BW and ADG. We conclude that supranutritional Se supplementation of ewes, primarily with SeY, positively affects later lamb performance measures (i.e., 60- and 120-day BW and ADG), and that these effects may be more pronounced for lambs of heavier breed (i.e., Suffolk) and lambs reared as twins.
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