J. Anim Sci. 2007. 85:1177-1183. doi:10.2527/jas.2006-067
© 2007 American Society of Animal Science
Efficacy of dietary selenium sources on growth and carcass characteristics of growing-finishing pigs fed diets containing high endogenous selenium
R. D. Mateo*,
J. E. Spallholz*,
R. Elder
,
I. Yoon
and
S. W. Kim*,1
* Texas Tech University, Lubbock, TX 79409;
and
Seaboard Foods, Shawnee Mission, KS 66202; and
and
Diamond V Mills Inc., Cedar Rapids, IA 52407
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Abstract
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A study was conducted to determine the efficacy of organic (Se-yeast, SelenoSource AF, Diamond V Mills Inc., Cedar Rapids, IA) and inorganic sources of Se on growth performance, tissue Se accretion, and carcass characteristics of growing-finishing pigs fed diets with high endogenous Se content. A total of 180 pigs at 34.4 ± 0.06 kg of BW were allotted to 1 of 5 dietary treatments: a negative control without added Se (NC); 3 treatment diets with 0.1, 0.2, or 0.3 mg/kg of added Se from an organic source; and a diet with 0.3 mg/kg of added Se as sodium selenite. Each treatment had 6 pens, with 6 pigs per pen-replicate. Experimental diets were changed twice at 66.1 ± 0.5 kg and 99.0 ± 0.9 kg of BW, and were fed until the pigs reached market weight. Growth performance was measured at the end of each phase. Upon reaching 129.9 ± 1.4 kg of BW, the pigs were transported to a local abattoir (Seaboard Foods, Guymon, OK), where carcass, loin, and liver samples were obtained. Hair and blood samples were obtained at the beginning and end of the study for Se analysis. Growth performance did not differ (P > 0.05) among treatments. Percent drip loss of the NC pigs was greater (2.41 vs. 1.75, P = 0.011) compared with pigs supplemented with Se. Pigs fed diets with added Se had greater Se concentrations in the liver (0.397 vs. 0.323 ppm, P = 0.015), loin (0.236 vs. 0.132 ppm, P < 0.001), serum (0.087 vs. 0.062 ppm, P = 0.047), and hair (0.377 vs. 0.247 ppm, P = 0.003) compared with the NC pigs. Percentage drip loss was linearly reduced [percent drip loss = 2.305 – (2.398 x Se), r2 = 0.29, P = 0.007] as dietary organic Se concentration increased. The Se concentration (ppm) in the liver [liver Se = 0.323 + (0.291 x Se), r2 = 0.33, P = 0.003], loin [loin Se = 0.122 + (0.511 x Se), r2 = 0.57, P < 0.001], serum [serum Se = 0.060 + (0.113 x Se), r2 = 0.33, P = 0.004] and hair [hair Se = 0.237 + (0.638 x Se), r2 = 0.56, P < 0.001] increased linearly as dietary organic Se concentration increased. Slope ratio analysis indicated that the relative bioavailability of organic Se for percent drip loss and loin and hair Se response was 306, 192, and 197% of that for inorganic Se, respectively. The results of the study show a potential advantage of organic Se supplementation in reducing drip loss even when the basal diet contains an endogenously high Se concentration of 0.181 ppm.
Key Words: carcass • drip loss • growth performance • pig • selenium
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INTRODUCTION
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Selenium has been established as an essential trace element that is important in many biochemical and physiological processes (Burk et al., 2003
). Research has shown that the organic and inorganic forms of Se vary in tissue retention and that organic Se is deposited in greater concentrations in many tissues compared with inorganic Se (Ku et al., 1973). Selenium, as a part of glutathione peroxidase, protects against oxidative stress. The protection of cell membranes from oxidation may help in improving water holding capacity of meat products. Mahan et al. (1999) reported that 0.3 ppm of organic Se in basal diets with an endogenous Se content of 0.06 ppm reduced drip loss and improved muscle color compared with inorganic Se supplementation. However, there is still limited information regarding the effects of different Se sources on carcass characteristics. Furthermore, most of the recent studies (Mahan and Parrett, 1996; Mahan et al., 1999) concerning the effectiveness of Se supplementation using different sources were conducted using feed ingredients with relatively low Se contents.
Considering the influence of geographical differences on Se concentration in feed grains (Mahan et al., 2005), mostly in the form of selenomethionine, the efficacy of supplemented Se from various sources should be tested in diets containing high concentrations of endogenous Se. Data regarding the effectiveness of organic Se supplementation to diets containing high concentrations of endogenous Se are limited.
The purpose of this study was to determine the efficacy of using organic (Se-yeast) and inorganic Se (sodium selenite) on growth performance, carcass characteristics, and tissue Se accretion in growing-finishing pigs fed diets containing high endogenous Se concentrations (>0.15 mg/kg).
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MATERIALS AND METHODS
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Animals and Design
The animal use and care protocol was approved by the Animal Care and Use Committee of Texas Tech University. A total of 180 pigs (Camborough 22 x PIC boar, Pig Improvement Company, Franklin, KY) at 34.4 ± 0.1 kg of BW were randomly allotted by sex to 1 of 5 dietary treatments. An experimental diet that contained no added Se served as the negative control (NC) diet. Three experimental diets were formulated to contain 0.1 (OS1), 0.2 (OS2), or 0.3 (OS3) ppm (all concentrations were in mg/kg) of added Se from an organic source (Se-yeast; SelenoSource-AF, Diamond V Mills Inc., Cedar Rapids, IA). An additional experimental diet (IS) contained 0.3 ppm of added Se from an inorganic source (sodium selenite, Southeastern Minerals Inc., Bainbridge, GA). Each treatment had 6 pens (3 barrow and 3 gilt pens) with 6 pigs per pen-replicate. The pen size was 2.1 x 3.6 m. Pigs were fed the experimental diets (Table 1) ad libitum from 34.4 ± 0.1 kg of BW until market weight (129.9 ± 1.4 kg of BW). The diets were changed at 66.1 ± 0.5 kg and 99.0 ± 0.9 kg of BW. Body weights and ADFI were measured at the end of each growth phase. Periods for each growth phase were 44, 38, and 27 d, which were coded as P4, P5, and P6, respectively. Morbidity and mortality of the pigs were monitored daily by trained farm staff.
Hair and Blood Sampling
Hair and blood samples were taken from 3 randomly selected pigs per pen at the beginning and at d 109 of the study. Hair samples were collected from the top of the shoulder (approximately 20 cm from both sides starting from the dorsal midline), which was first brushed to remove nonhair matter. Collected hair samples were then washed with distilled water, rinsed, air-dried, and stored in plastic bags for Se analysis. Pigs with nonwhite skin or spots were excluded from sampling because the Se content in swine hair can be influenced by color (Kim and Mahan, 2001b). Hair samples were pooled by pen at each sampling and were later analyzed for Se concentrations. Blood samples were obtained in the morning at 1000 and were collected by jugular venipuncture using 9-mL tubes (Sarstedt Inc., Newton, NC). Blood samples were immediately placed on ice. The samples were centrifuged at 2,000 x g for 15 min; serum was collected, transferred into 1.5-mL microcentrifuge tubes (National Scientific, San Rafael, CA) and stored at –20°C for determination of Se concentrations.
Tissue and Feed Sampling and Carcass Measurement
Upon reaching 129.9 ± 1.4 kg of BW, all pigs were transported to a local abattoir (Seaboard Foods, Guy-mon, OK) to obtain carcass data. Hot carcass weight was obtained after slaughter just before chilling. The loin was cut (24-h postmortem) between the 10th and 11th rib, and then the exposed LM was measured for loin depth. Last-rib, carcass backfat thickness was determined by measuring the dorsal, midline fat thickness, including skin, opposite to the last rib. Loin weight was also obtained. Percent lean was calculated by using carcass weight as fat free lean (kg) divided by warm carcass weight multiplied by 100. The formula for fat free lean (kg) was {5.77 + [1.006 x sex (barrow = 1, gilt = 2)] – (18.838 x 10th rib fat depth) + (4.357 x 10th rib loin muscle area) + (0.401 x warm carcass weight)}/2.2. Determination of the 24-h loin pH and temperature was obtained from the loin muscle between the 10th and 11th rib. The pH of the loin muscle was determined using a portable pH meter (Model IQ 140 pH Meter, IQ Scientific Instruments Inc., Carlsbad, CA). Hunter L (luminescence), a (redness), and b (yellowness) values were obtained using a Minolta color recorder (MiniScan XE Plus, Hunter, Reston, VA). Water holding capacity was determined using the drip loss method as described by Gentry et al. (2002). Loin muscle samples were obtained using a 2.54-cm-diam. coring device. Samples were placed in preweighed plastic drip loss tubes (meat juice containers, C. Christensen Laboratory, Hillerod, Denmark) equipped with a collection funnel. The drip loss tubes together with the sample were again weighed and were held at 4°C for 48 h (24 to 72 h postmortem). Drip loss tubes with only the exudates were then reweighed, and amount of drip loss was determined as a percentage of initial weight. Visual color scores were determined from a scale of 1 to 6 (1 = pale, pinkish gray and 6 = dark, purplish red) using Japanese color standards. Firmness, marbling, and texture measurements were determined by trained personnel using 5-point scales (NPPC, 2000), wherein firmness scores ranged from 1 = very soft to 5 = very firm, marbling ranged from 1 = devoid to practically devoid to 5 = moderately abundant or greater and texture ranged from 1 = coarse to 5 = fine, respectively.
Loin and liver samples were obtained and stored at –20°C until Se analysis. Liver and loin samples ranging from 0.1 to 0.4 g and blood serum (1 mL) samples were obtained based on wet weight and placed in 15- x 125-mm test tubes (Fisher Scientific, Pittsburgh, PA) for Se determination (Spallholz et al., 1978). Feed from each treatment diet was subsampled, and 8 subsamples per treatment for each phase were used for determining Se concentration. All measurements on each subsample were done in triplicate. A stock Se solution was prepared from sodium selenite used as the standard. The Se content in feed, hair, tissue, and serum samples were prepared for analysis by the fluorometric method, as described by Spallholz et al. (1978).
The analyzed Se concentration of the basal diet was 0.181 ppm (Table 2). The analyzed Se concentration of the feeds with added Se above the basal diet from the organic source was 0.135, 0.243, and 0.361 ppm for the OS1, OS2, and OS3 diets, respectively. The IS diet contained 0.288 ppm of Se.
Statistical Analyses
Statistical analysis was performed using the GLM procedure (SAS Inst. Inc., Cary, NC). Differences among treatment means were evaluated using the PDIFF option of SAS software. Pen was the experimental unit. Orthogonal contrasts were done to compare the negative control with the groups supplemented with Se. Regression analysis (PROC REG) was done to determine the relationship between the tissue Se content and added dietary Se concentrations. A slope ratio assay (Littell et al., 1997; Kim and Easter, 2001) was derived for the effects of added dietary Se concentrations by source on percent drip loss and Se concentration in tissues. The relative bioavailability was then determined by comparing the slopes of the regression lines with a common intercept. The actual analyzed Se concentration of the feeds was used in all statistical analyses.
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RESULTS
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Diet Se Concentrations
The analyzed Se content of the diet containing added Se from the inorganic source was lower, whereas it was greater in the diets containing added Se from the organic source than targeted concentrations (Table 2
).
Growth Performance
The ADG of the pigs during P4, P5, and P6 did not differ (P = 0.426, 0.672, and 0.610, respectively; data not shown) among treatments. Likewise, ADG of pigs during the entire experimental period did not differ among treatments (P = 0.363; Table 3). No differences in ADFI were observed among treatment groups during each phase (P = 0.549, 0.647, and 0.507 for P4, P5, and P6, respectively; data not shown) nor during the entire experimental period (P = 0.395; Table 3). The G:F did not differ among the treatment groups during each feeding phase (data not shown) nor during the entire experimental period (P = 0.286; Table 3).
Carcass Characteristics
Hot carcass weight (P = 0.989) and last rib backfat thickness (P = 0.333) of pigs did not differ among treatments (Table 4). Loin depth including lean percentage was the same (P = 0.762 and P = 0.334, respectively) among the treatments. However, loin weight of the OS1 tended to be greater (P = 0.067) than the OS2. Visual color score did not differ (P = 0.366) among treatments, nor did loin color (Minolta L, a, and b; P = 0.882, P = 0.887, and P = 0.825, respectively). Loin pH and loin temperature 24 h postmortem among treatment groups did not differ (P = 0.598 and P = 0.969, respectively); neither did values for firmness (P = 0.440), texture (P = 0.334), or marbling (P = 0.233). The percent drip loss measured during a 48-h period from loin of pigs fed the IS diet did not differ (1.93 vs. 2.41; P = 0.128) from the NC group. The percent drip loss from loin of pigs fed NC diet was greater (2.41 vs. 1.75, P = 0.011) than for pigs fed diets with Se supplementation. Furthermore, percent drip loss was reduced linearly (percent drip loss = 2.305 – 2.398 x Se, r2 = 0.29, P = 0.007) as the added dietary Se concentration from the organic Se source increased. Multiple linear regression analysis indicated that the slope of the percent drip loss obtained based on added dietary Se concentration for the organic Se was 306% (P = 0.025) that of the inorganic Se source (Figure 1). These results suggest that the organic source was more effective in reducing percent drip loss.
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Figure 1. Changes in percent drip loss as added dietary Se concentration (ppm) increases in pigs fed diets containing organic or inorganic Se.
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Tissue Se Concentration
Liver Se concentrations of pigs fed the IS diet did not differ (0.400 vs. 0.323 ppm; P = 0.066) from liver Se concentration of pigs fed the NC diet. Pigs fed diets supplemented with Se had greater liver Se concentrations (0.397 vs. 0.323 ppm, P = 0.015) than NC-fed pigs (Table 5). Liver Se content increased linearly (liver Se = 0.323 + 0.291 x Se, r2 = 0.33, P = 0.003) as added dietary Se concentrations from the organic Se source increased. Multiple linear regression analysis indicated that slopes for liver Se concentration based on added dietary Se concentrations for both Se sources did not differ (P = 0.713) from each other (Table 6), suggesting that both Se sources were equally available for liver Se deposition.
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Table 5. Liver, loin, serum, and hair Se concentrations (ppm) of pigs fed diets with different dietary concentrations and sources of Se
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Table 6. Relative bioavailability values for percent drip loss and tissue Se concentrations of pigs fed diets supplemented with 2 Se sources1
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The loin Se concentration for the IS group was greater (0.201 vs. 0.132 ppm; P < 0.001) compared with loin Se concentration of pigs fed the NC diet. The loin Se concentration was also greater (0.236 vs. 0.132 ppm, P < 0.001) in pigs fed diets supplemented Se compared with the NC. Loin Se content increased linearly (loin Se = 0.122 + 0.511 x Se, r2 = 0.57, P < 0.001) as the added dietary Se concentration from the organic source increased. Multiple linear regression analysis indicated that the slope of the loin Se concentration based on added dietary Se concentration for the organic source was 192% (P = 0.012) that of the inorganic Se (Table 6). This suggests that the organic Se was more available than inorganic Se in terms of loin Se deposition.
The average initial serum Se concentration was 0.05 ppm. Serum Se concentration of pigs fed diets supplemented with inorganic Se did not differ (P = 0.077) from pigs fed the NC diet. Pigs supplemented with Se had greater serum Se concentrations (0.087 vs. 0.062 ppm, P = 0.047) than pigs fed the NC diet. Results also showed a linear increase (serum Se = 0.060 + 0.113 x Se, r2 = 0.33, P = 0.004) in serum Se concentration as the added dietary Se concentrations from the organic Se source increased. Multiple linear regression analysis indicated that the slopes for serum Se concentration based on added dietary Se concentration for both Se sources did not differ (P = 0.561) from each other, suggesting similar relative bioavailability in terms of serum Se deposition between Se sources (Table 6).
The average initial hair Se concentration was 0.26 ppm. Hair Se concentration of pigs fed the IS diet did not differ (P = 0.110) from pigs fed the NC diet. The hair Se concentration from pigs supplemented with Se was greater (0.377 vs. 0.247 ppm, P = 0.003) compared with the NC. The hair Se concentration also increased linearly (hair Se = 0.237 + 0.638 x Se, r2 = 0.56, P < 0.001) as the added dietary Se concentrations from the organic source increased. Multiple linear regression analysis indicated that the slope of the hair Se concentration based on the added dietary Se concentration for organic Se was 197% (P = 0.033) that of the inorganic Se suggesting that the organic Se source was more available relative to the inorganic Se source based on hair Se deposition (Table 6).
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DISCUSSION
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Growth performance data suggest that Se supplementation, regardless of the Se source or amount fed in the study, did not improve growth beyond the basal diet with 0.181 ppm Se, which is slightly greater than the recommended dietary Se level (0.150 ppm) by the NRC (1998) for growing-finishing pigs. Previous studies (Mahan and Parrett, 1996; Mahan et al., 1999) where the basal diets contained lower endogenous Se concentrations (0.039 to 0.060 ppm) also did not show improved growth performance with Se supplementation.
Of carcass traits measured, only 48-h drip loss of loins was improved by organic Se supplementation. Results showed that the organic Se source was more effective in reducing percent drip loss compared with the inorganic Se source used in the study. Similar results relative to drip loss have also been reported in chickens fed organic vs. inorganic Se (Downs et al., 2000; Choct et al., 2004). Mahan et al. (1999) reported greater drip loss from pigs fed inorganic Se as sodium selenite compared with pigs fed organic Se (Se-enriched yeast). They also reported that pigs supplemented with inorganic Se had lighter (paler) colored muscle. However, in the current study no differences were observed in muscle color among treatments. This may be partially due to the greater endogenous Se concentration (0.181 ppm) of the basal diet compared with the basal diet Se in Mahan et al. (1999; 0.18 vs. 0.06 ppm). In addition, dietary basal levels of vitamin E used in the current study were also greater than those used by Mahan et al. (1999; 41.3 vs. 22 IU/kg).
Selenium, as a part of the enzyme glutathione peroxidase, works as an antioxidant by reducing hydrogen peroxide, providing protection to cellular and subcellular membranes against oxidative damage (NRC, 1983). It has been reported that selenite at high dietary concentrations may have a prooxidant characteristic (Spallholz, 1994) which can potentially damage cellular components. Seko et al. (1989) reported that hydrogen selenide formed via reduction of selenite with reduced glutathione reacts directly with O2 to generate the superoxide anion. Oxidative properties of selenite have also been reported by Terada et al. (1999) and Lipinski (2005). On the other hand it has been reported that selenomethionine is not as toxic to cells in culture or to animals (Spallholz et al., 2004). However, in this study, percent drip loss did not differ between the IS and the OS3 group (1.93 vs. 1.43; P = 0.115). It should be noted that the analyzed Se concentration was lower for the IS group compared with the OS3 group (0.288 vs. 0.361 ppm).
Slope ratio analysis showed that the organic Se was more available for deposition in tissues such as loin and hair. Most of the naturally occurring Se in plants is in the form of selenomethionine, which is also the predominant form in Se-enriched yeast (Ip et al., 2000; Schrauzer, 2000). It has been previously reported that feeding diets with selenomethionine as the source of Se resulted in greater tissue accumulation of Se than other forms of Se (Mahan and Parrett, 1996; Kim and Mahan, 2001a; Taylor et al., 2005). It has been demonstrated that selenomethionine has greater bioavailability than inorganic Se (Beilstein and Whanger, 1986) and that the increase in its absorption and storage is due to its direct incorporation into proteins (Combs and Combs, 1986). Although selenite can be utilized for selenoprotein biosynthesis, only selenomethionine can be incorporated nonspecifically into body proteins in place of methionine (Ip, 1998; Schrauzer, 2000) allowing Se to be stored in the animal body tissue proteins. The difference in metabolism between the inorganic and organic forms of Se most likely accounts for the differences in the concentrations of Se in tissues. However, in this study, concentrations of Se in the liver and serum were the same for both Se sources. In addition to the relatively high Se concentrations in the basal diet, similar concentrations for both Se sources in serum and liver tissue may related to the high rate of protein turnover occurring in these tissues.
Depending on where crops were grown, common feed ingredients used in swine diets such as corn and soybean meal contain different amounts of Se. In some parts of the US, especially states in the high plains and southwestern regions (i.e., CO, KS, LA, ND, NE, NM, OK, SD, and TX) have soils that are naturally high in Se. Approximately 80% of all grains grown in these parts of the United States contain greater than 0.1 ppm Se, whereas other parts may contain less (Kubota et al., 1967). A recent collaborative study by NCCC-42 Swine Nutrition Committee (Mahan et al., 2005) showed regional differences in terms of Se concentration. Furthermore, these regional variations in grain were reflected in concentrations of tissue Se. The current study was conducted using corn and soybean meal that contained high concentrations of endogenous Se.
Results have shown that even with the high concentrations of endogenous Se in the diet, supplementation of Se with organic source resulted in reduced drip loss from loins. The results of this study suggest that Se supplementation with organic Se may improve pork quality and provide greater Se intakes for consumers.
1 Corresponding author: sungwoo.kim{at}ttu.edu
Received for publication February 5, 2006.
Accepted for publication January 24, 2007.
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Abstract
INTRODUCTION
