J. Anim Sci. 2006. 84:1729-1733. doi:10.2527/jas.2005-311
© 2006 American Society of Animal Science
Comparative effects of organic and inorganic selenium on selenium transfer from sows to nursing pigs
I. Yoon*,1 and
E. McMillan
* Diamond V Mills Inc., Cedar Rapids, IA 52407; and
and
MapleLeaf Foods Agresearch, Burford, Ontario, NOE 1AO, Canada
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Abstract
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To investigate the effects of supplemental Se on the transfer of Se to nursing pigs when sows are fed diets containing a Se level above the NRC recommendation (0.15 ppm), sows were fed diets containing no supplemental Se or supplemental (0.3 ppm) Se from sodium selenite or Se yeast. A nonSe-fortified corn-soybean meal basal diet with a high endogenous Se content served as the negative control (0.20 to 0.23 ppm Se). Fifty-two sows were fed diets from 60 d prepartum until 14 d of lactation. Six sows per treatment were bled at 60 and 30 d prepartum, at farrowing, and at 14 d postpartum to measure serum Se concentrations. Colostrum was collected within 12 h postpartum, and milk was collected at 14 d of lactation. Blood was obtained from 3 pigs each from 12 litters per treatment at birth and at weaning (d 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 (P < 0.06) to have greater serum Se at farrowing than sows fed unsupplemented diets. Colostrum and milk (d 14) Se concentrations increased (P < 0.01) when sows were fed Se from yeast but not from sodium selenite. At birth, serum Se was increased (P < 0.01) for pigs whose dams were fed Se yeast compared with pigs from sows fed the basal diet. At 14 d of age, there was no difference in serum Se concentration of pigs from dams fed any of the treatments. Pig serum immunoglobulin G concentrations and glutathione peroxidase-1 activity were unaffected by dietary Se source. Supplementation of gestating and lactating sow diets with Se (0.3 ppm) from an organic or inorganic source reduced the number of stillbirths per litter. However, only pigs born to sows fed organic Se (Se yeast) had greater serum Se at birth. Organic Se increased Se concentration of colostrum and 14-d milk to a greater degree than inorganic Se.
Key Words: nursing pig • selenium transfer • selenium yeast • sodium selenite • sow
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INTRODUCTION
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Selenium status of pigs at birth and weaning can be affected by the sow’s body 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 (<0.1 mg/kg). 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. Mahan et al. (2005) reported high correlation between dietary Se and tissue Se concentrations when inorganic Se was supplemented, but the high correlation was attributed to the endogenous organic Se from the grain source, rather than from added sodium selenite. Mateo et al. (2005) reported that inorganic Se was not as effective in accumulating Se in tissues as organic Se. The additional benefits of feeding supplemental Se above NRC recommendation, especially from Se yeast, are unclear. Therefore, a study was conducted to investigate effects of inorganic and organic Se sources in gestation and lactation diets with high endogenous Se concentrations from the cereal grains comprising the basal diets.
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MATERIALS AND METHODS
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Animals, Housing, and Experimental Design
All animals were reared and handled in accordance with the Guidelines of the Canadian Council of Animal Care. Pregnant sows (Yorkshire x Landrace; n = 52) were fed diets containing no supplemental Se or 0.3 mg/kg as-fed of supplemental Se from an inorganic (sodium selenite) or organic (Se-enriched yeast, SelenoSource AF, Diamond V Mills, Cedar Rapids, IA) source to examine the effects of Se source on transfer to the dam’s milk and thereby to the nursing pigs.
Sows were allotted by parity and BW within 9 farrowing groups to 1 of the 3 treatments beginning 60 d prepartum. Sows were distributed to groups of 3 by parity such that all sows in the group were within 1 parity unit (i.e., group 1 = parity 2 and 3; group 7 = parity 6 and 7). Within the group, sows farrowed within 7 d of each other. At 2 d prepartum, the sows were moved into an environmentally controlled farrowing house, where they were fed a lactation diet containing their respective treatment until weaning at 14 d postpartum. The experiment began with 54 sows, but 2 sows were removed from the study because of reproductive failure before farrowing. Therefore, the control group had 18 sows, and the Se-supplemented groups had 17 sows each. Gestation and lactation diets were formulated to exceed NRC (1998) nutrient requirements and contained 0.20 and 0.23 ppm Se, respectively, before addition of supplemental Se (Table 1). Diets were provided at 2.5 kg daily during the gestation period. Sows were fed ad libitum during the lactation period.
Sample Collection and Laboratory Analysis
Blood was collected by jugular venipuncture from a random subset of pregnant sows (n = 6 per treatment) on d –60, –30, 0 (day of parturition), and 14 postpartum, and serum Se concentration was determined. The same subset of sows was bled at each time period. All blood was collected into sterile vacutainer tubes (10 mL). The blood remained at room temperature for 1 h to allow the clot to form. The samples were centrifuged in a clinical centrifuge at 433 x g for 10 min, and the serum was pipetted into plastic vials. The serum samples were frozen (–20°C) until analysis.
Within 12 h after farrowing, colostrum was collected, and milk was collected from the same sows at 14 d postpartum. At d 0, colostrum was collected by hand-expression from several glands. At weaning on d 14, 1 mL of oxytocin (20 IU) was given to facilitate milk letdown before expressing the milk from the glands. Approximately 10 mL was collected each time. Colostrum and milk samples were frozen (–20°C) before analysis for Se.
Blood was collected at birth and weaning from 3 randomly selected piglets per litter from 12 litters per treatment. Serum was pooled within litter by adding the same amount of serum from the 3 piglets before analyses for Se and immunoglobulin G (single immunodiffusion; Harlow and Lane, 1988) concentrations, and glutathione peroxidase (GPX) activity. Pooled blood samples were used to obtain a sufficient amount of blood for analyses and to minimize individual variation. All serum samples were frozen (–20°C) before analysis.
Serum GPX activities were determined according to the method of Paglia and Valentine (1967) using the test kit RANSEL (Randox Laboratories, Ltd., United Kingdom). The RANSEL kit measures the GPX-1 activity, although it may also measure trace amounts of GPX-3 isomer activity. In the presence of glutathione reductase and NADPH, the oxidized glutathione is converted to reduced form, with a concomitant oxidation of NADPH to NADP+. The decrease in absorbance is measured at 340 nm and 37°C (Beckman-Coulter Model CX5 Delta, Global Medical Instrumentation Inc., Ramsay, MN). The enzyme activity necessary to convert 1 µmol of NADPH to NADP+ in 1 min is defined as the GPX unit, and the result is expressed as units of GPX per milliliter of serum. Feed samples were obtained from each batch of feed, composited, and stored (–20°C) before analyses. Approximately 0.5 g of feed samples from each treatment diet was used to measure Se concentration. Concentrations of Se in feed, colostrum, milk, and serum were measured using the fluorometric method outlined by AOAC (2000).
Statistical Analysis
Data were analyzed using the GLM procedure of Minitab (Release 13.32, Minitab Inc., State College, PA) using a randomized complete block design (Steel and Torrie, 1980). Parity of sows (first parity, second to fifth parity, over fifth parity) was the blocking factor. Sow and litter were considered the experimental unit for variables associated with sow and piglet data. For the sow serum Se, terms for group, time, treatment, and their interactions were included in the model. For factors with significant differences, Tukey’s LS mean test was used for comparison of means. Least squares means are presented. Significance was declared at P < 0.05 and trends at P < 0.10.
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RESULTS AND DISCUSSION
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Selenium Level in the Diets
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 0.3 ppm), dietary Se ranged from 0.227 to 0.651 ppm. In our study, feed ingredients were obtained from Eastern Canada. Selenium from basal ingredients alone provided 0.20 ppm for gestation diets and 0.23 ppm for lactation diets. These concentrations are greater than the NRC (1998) recommendation of 0.15 ppm. When supplemented, the gestation diets analyzed 0.42 ppm Se for sodium selenite and 0.41 ppm Se for Se yeast and for lactation diets, 0.49 ppm Se for sodium selenite and 0.50 ppm for Se yeast.
Reproductive Performance
Supplementation with either form of Se reduced (P < 0.05) the number of nonviable piglets born (Table 2). Much of this was due to a reduction (P < 0.05) 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 4 consecutive parities (Mahan and Peters, 2004).
Serum Measurements
Sow serum Se concentrations (Table 3) did not differ by treatment at the beginning of the trial. However, serum Se concentrations tended (P = 0.06) 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 d (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.
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Table 3. Serum Se concentrations (µg/mL) of sows fed inorganic or organic Se sources during gestation and lactation1
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Regardless of treatment, serum Se concentration declined (P < 0.01) from gestation to parturition (Table 3
). Mahan and Peters (2004) also reported the decline in serum Se from 70 to 110 d postcoitum in all treatment groups. Mahan and Kim (1996) speculated that the decline might reflect a greater demand for Se to produce selenoproteins 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% 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 (P = 0.01) with organic Se in the sow’s diets than pigs whose dams were fed the nonsupplemented control (Table 4). Serum Se concentrations in pigs at birth from sows fed the inorganic Se were not different (P > 0.05) from the pigs of sows fed the control or the organic Se diet. At weaning, there were no differences (P = 0.53) in serum Se concentration of pigs from sows fed any of the dietary treatments. Research by Gunther et al. (2003) showed that calves from cows fed Se yeast had greater whole blood Se concentrations at birth than calves from cows fed no Se or sodium selenite.
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Table 4. Pooled serum Se, immunoglobulin G, and glutathione peroxidase (GPX-1) activity in piglets of sows fed inorganic or organic Se sources during gestation and lactation1
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Serum immunoglobulin and GPX-1 did not differ (P > 0.05) for pigs from sows regardless of dietary treatment. There was a tendency (P = 0.07) for pigs from sows fed inorganic Se to have greater GPX-1 at birth (Table 4). Results of Mahan (2000) indicated that serum GPX activity increases as the pigs age, but activity is not influenced by supplemental Se source even when there is an increase in the serum Se concentration due to supplemental Se. Mahan and Kim (1996) reported that serum GPX activity in weanling pigs was similar regardless of Se concentration or Se source fed to the dam, although serum Se increased when the dams were fed either inorganic or organic Se. These data indicate that serum GPX is less sensitive to change in dietary Se source and concentration.
Colostrum and Milk Selenium
Colostrum and milk Se concentrations increased (P = 0.01) when organic Se was fed but not with inorganic Se supplementation (Table 5). Mahan and Peters (2004) reported that Se concentrations in colostrum and milk at weaning (21 d for parity 1 sows and 17 d for parity 2 to 4 sows) increased for both organic and inorganic Se sources, but were substantially greater (P < 0.01) 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 postweaning; 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 slower 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 14 d milk to a greater degree than inorganic Se.
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IMPLICATIONS
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Supplementation of the gestating and lactating sow diets with Se from an organic source at the concentration of 0.30 parts per million selenium can be beneficial, even when sows are receiving a relatively high concentration of selenium (over 0.20 parts per million selenium) 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.
1 Corresponding author: iyoon{at}diamondv.com
Received for publication June 10, 2005.
Accepted for publication February 3, 2006.
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Abstract
INTRODUCTION
