It is well documented that the grains and forages produced in many parts of the world contain Se concentration that ranges from deficient to toxic (Oldfield, 1999). In the United States, results from a collaborative study involving 19 states (Mahan et al., 2005) suggest that high variation exists in endogenous Se concentrations in grains. When supplemented with inorganic selenite (0 to 0.3ppm), dietary Se ranged from 0.227 to 0.651ppm. In this study, feed ingredients were obtained from Eastern Canada. Selenium from basal ingredients alone provided 0.20ppm for gestation diets and 0.23ppm for lactation diets. These concentrations are greater than the NRC (1998) recommendation of 0.15ppm. When supplemented, the gestation diets analyzed 0.42ppm Se for sodium selenite and 0.41ppm Se for Se yeast and for lactation diets, 0.49ppm Se for sodium selenite and 0.50ppm for Se yeast.
Selenium status of pigs at birth and weaning can be affected by the sow’s body selenium (Se) reserves, dietary Se concentration, and source of Se (Mahan et al., 1974; Mahan, 2000; Mahan and Peters, 2004). Reported benefits of feeding organic Se from Se-enriched yeast include increased Se biomarkers in both the sow and progeny (Mahan and Kim, 1996). Most of the published studies were performed using basal diets with very low Se content. However, basal grains grown in some areas of the world may contain adequate Se (Oldfield, 1999), resulting in a Se concentration in the diet that reaches or exceeds the NRC (1998) recommendation of 0.15 mg/ kg Se in sow diets before Se supplementation.
In this particular study, 52 sows were fed diets from 60 days prepartum until 14 days of lactation. Six sows per treatment were bled at 60 and 30 days prepartum, at farrowing, and at 14 days postpartum to measure serum Se concentrations. Colostrum was collected within 12 hours postpartum, and milk was collected at 14 days of lactation. Blood was obtained from 3 pigs each from 12 litters per treatment at birth and at weaning (day 14), and pooled serum was analyzed for Se and immunoglobulin G concentrations and glutathione peroxidase activity. Regardless of treatment, serum Se in sows declined throughout gestation and gradually increased during lactation. Sows fed Se yeast tended to have greater serum Se at farrowing than sows fed diets that were not supplemented. Colostrum and milk (day 14) Se concentrations increased when sows were fed Se from yeast but not from sodium selenite.
Reproductive Performance
Supplementation with either form of Se reduced the number of non-viable piglets born. Much of this was due to a reduction in the number of stillborn piglets. A similar response was observed by Mahan and Peters (2004). Source of Se did not affect the number of pigs per litter, piglet birth weight, or litter gain from birth to weaning. In a previous study, dietary Se source fed in late pregnancy did not affect reproductive performance of sows (Mahan, 2000). However, reproductive performance of sows fed supplemental Se improved when sows received treatment diets for four consecutive parities (Mahan and Peters, 2004).
Serum Measurements
Sow serum Se concentrations did not differ by treatment at the beginning of the trial. However, serum Se concentrations tended to be greater for sows fed organic Se at farrowing. The differential effect between Se yeast and sodium selenite on blood Se concentration previously has been reported. Dairy heifers fed Se yeast had increased whole blood Se concentrations at calving compared with heifers fed inorganic Se when the animals were supplemented for 60 days (Wallace et al., 2005). Payne and Southern (2005) reported that dietary supplementation with Se yeast increased plasma Se concentration in broilers compared with birds fed the control diet or the diet with sodium selenite.
Regardless of treatment, serum Se concentration declined from gestation to parturition. Mahan and Peters (2004) also reported the decline in serum Se from 70 to 110 days post-coitum in all treatment groups. Mahan and Kim (1996) speculated that the decline might reflect a greater demand for Se to produce seleno-proteins or Se transfer to fetal or mammary tissue during late pregnancy and lactation, respectively. Therefore, it would be critical to supply the proper amount or form of Se during this phase of the reproductive cycle.
More than 70 percent of total Se in Se yeast used in this study was in the form of selenomethionine (Se-Met). Pigs fed Se yeast had greater concentrations of Se in most tissues than pigs fed inorganic selenite (Mateo et al., 2005; Mahan and Kim, 1996). Much of the body’s Se is in proteins as Se-Met. As proteins in the body are turned over, Se- Met is released and, if broken down, can provide Se for physiological needs (Schrauzer, 2000).
Piglet serum Se concentration was greater at birth with organic Se in the sow’s diets than pigs whose dams were fed the non-supplemented control. Serum Se concentrations in pigs at birth from sows fed the inorganic Se were not different from the pigs of sows fed the control or the organic Se diet. At weaning, there were no differences in serum Se concentration of pigs from sows fed any of the dietary treatments.
Colostrum and Milk Selenium
Colostrum and milk Se concentrations increased when organic Se was fed but not with inorganic Se supplementation. Mahan and Peters (2004) reported that Se concentrations in colostrum and milk at weaning (21 days for parity 1 sows and 17 days for parity 2 to 4 sows) increased for both organic and inorganic Se sources, but were substantially greater when sows were fed organic Se.
Results of both studies suggest that Se from sodium selenite was less effectively incorporated into milk of lactating sows than Se from an organic source. Significant increases in milk Se concentrations were observed when cows were fed Se yeast compared with cows fed either sodium selenite (Givens et al., 2004) or sodium selenate (Knowles et al., 1999). The relative response in milk Se concentration is much greater than the response in blood, probably because milk protein contains more methionine than does blood (NRC, 2001).
More Se-Met will be incorporated into milk protein than blood protein because cells cannot tell the difference between methionine and Se-Met. Mahan (2000) suggested that because Se status of weaned pigs is critical to preventing the onset of a Se deficiency post-weaning; incorporating organic Se into diets of gestating and lactating sows could improve Se status of nursing pigs and might prevent the onset of Se deficiency. Feeding organic Se to the dams effectively increased colostrum and milk Se concentration and serum Se concentration of pigs at birth. Mahan (2000) hypothesized that when organic Se is fed to sows, less Se is retained in muscle and liver tissue because those tissues are turning over more slowly than those of grower-finisher pigs; consequently, more absorbed organic Se would be available to mammary tissue for incorporation into milk. Results of this study indicated that organic Se consumed by the sows increased serum Se concentration of piglets at birth and Se concentration of colostrum and milk at 14 days to a greater degree than inorganic Se.
Implications
Supplementation of the gestating and lactating sow diets with selenium from an organic source at the concentration of 0.30 ppm Se can be beneficial, even when sows are receiving a relatively high concentration of selenium (over 0.20 ppm) through basal ingredients. Organic and inorganic selenium were equally effective in decreasing stillbirths. However, only selenium yeast increased colostral and milk selenium, even if a sow’s diet contains a high innate concentration of selenium.
Editor’s Note: This content for this commentary is based on a study by I. Yoon, with Diamond V Mills, Inc., Cedar Rapids, IA; and E. McMillan, Maple Leaf Foods Agresearch, Burford, Ontario, Canada and is sponsored by Alltech. Through 29 years of research-driven product development, Alltech has created a range of natural solutions for the feed and food industries. For more information, please visit the Web sites at www.alltech.com.
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