Introduction

Selenium is essential for the normal development of sperm cells and is also a component of glutathionine peroxidase, an enzyme that is an antioxidant for cellular membrane lipids and protects cellular components against free radicals (Hansen and Deguchi, 1996). Several research groups reported that selenium supplementation had little effect on the growth performance of boars. Indeed, growth rates, feed intakes, feed conversion efficiencies, and testicular sizes were similar for control boars and boars provided extra selenium in the diet (0.5 ppm; Kolodziej and Jacyno, 2005; Marin-Guzman et al., 1997) or via subcutaneous injections at 14-day intervals (0.33 mg/kg body weight; Segerson et al., 1981).

In contrast to those reports, Henson et al. (1983) reported that boars fed diets supplemented with selenium exhibited some signs of retarded growth and sexual development. In that study, boars were fed a basal corn and soybean meal diet (0.05 ppm selenium) or the basal diet supplemented with a selenium premix at concentrations of either 0.1 (n = 11) or 0.25 ppm (n = 11). Experimental diets were fed on a free choice basis from 54 days of age until approximately 6 months of age, and were then limit fed at a rate of 5.0 pounds/boar/day. Treatment by age interactions existed for body weights, testis width, libido (subjectively scored twice weekly upon exposure to ovariectomized, estrogen-treated gilts), and plasma testosterone levels, and in general, values were greater for boars fed the basal diet than for those fed the basal diet supplemented with selenium.

Jacyno et al. (2002) conducted an experiment during which boars were fed diets supplemented with either 0.2 ppm organic selenium (selenium-yeast) and 60 ppm vitamin E (n = 40), or 0.2 ppm inorganic selenium (sodium selenite) and 30 ppm vitamin E (n = 40). The study was conducted from 70 to 180 days of age in both the summer and winter seasons, and the daily feed ration was gradually increased along with increasing body weight. Compared with boars that received the organic source of selenium, boars receiving the inorganic selenium had higher average daily gain and better feed conversion efficiency, effects that were most pronounced during the winter. There were no effects of treatment on leanness or testicular size. The results of this experiment are difficult to interpret, however, because source of selenium was confounded with concentration of vitamin E fed.

Given the equivocal results generated in previous research, we conducted an experiment the objective of which was to compare growth performance and carcass characteristics in crossbred boars fed diets supplemented with selenium from either organic or inorganic sources.

Materials and Methods

Yorkshire x Landrace boars (n = 117; 18.3 pounds body weight) weaned at approximately 28 days of age, were blocked by body weight, placed in nursery pens (three boars/pen) and assigned from within block to three treatments: I. a basal diet (NRC, 1998) with no supplemental selenium (controls), II. basal diet supplemented with 0.3 ppm organic selenium (Sel-Plex; Alltech, Inc., Nicholasville, KY) and, III. basal diet supplemented with 0.3 ppm sodium selenite (Premium Selenium 270; North American Nutrition Co., Inc., Lewisburg, OH) (n = 13 pens/treatment). Boars had free choice access to feed and water during the 5-week nursery phase.

Boars were then moved to a grower-finisher barn and continued to receive, on a free-choice basis, either a basal diet or a basal diet supplemented with either 0.3 ppm Sel-Plex or sodium selenite (n = 11 pens/treatment). The trial ended when boars weighed an average of 300.7 pounds. One boar from each pen was then slaughtered and carcasses were evaluated. Blood samples were collected at the end of the nursery and growing-finishing phases for determination of selenium concentrations by atomic absorption analysis. All data were analyzed using analysis of variance (SAS Institute Inc., Cary, NC).

Results and Discussion

Table 1. Growth performance during the 5-week nursery phase in boars fed a diet with no supplemental selenium (controls) or diets supplemented with 0.3 ppm selenium from organic Sel-Plex or inorganic sodium selenite.
Item:	Control	Sel-Plex	Sodium Selenite	SE	P
No. of pens1	13	13	13	---	---
Average daily gain (pounds)	1.05	1.03	1.03	0.03	0.92
Average daily feed intake (pounds)	1.98	1.98	1.97	0.06	0.98
Feed/gain	1.85	1.86	1.87	0.04	0.95
1 Each pen contained 3 boars. Sources: Organic Sel-Plex; Alltech, Inc., Nicholasville, KY, inorganic (sodium selenite; Premium Selenium 270; North American Nutrition Co., Inc., Lewisburg, OH) sources.

Growth performance for the growing-finishing phase and carcass characteristics are shown in Table 2 and 3, respectively. Among groups, average daily gain and average daily feed intake were similar (P > 0.1). Feed/gain was affected by treatment (P = 0.02) and was lower (P < 0.06) for boars fed Sel-Plex compared with boars fed sodium selenite or controls. At slaughter, there were no effects of treatment on hot carcass weight, dressing percent, carcass length, loin muscle area, or tenth or last rib backfat thickness (P > 0.1). First rib backfat thickness tended to be affected by treatment (P = 0.08) and was greater (P < 0.06) in controls and Sel-Plex-fed boars compared with boars fed sodium selenite. Blood selenium concentrations (ppb) were higher (P < 0.01) in boars consuming Sel-Plex (198.9 + 5.5) than in boars consuming sodium selenite (171.4 + 5.4) or controls (26.7 + 5.4).

Table 2. Growth performance during the grow-finish phase in boars fed a diet with no supplemental selenium (controls) or diets supplemented with 0.3 ppm selenium from organic Sel-Plex or inorganic sodium selenite.
Item:	Control	Sel-Plex	Sodium Selenite	SE	P
No. of pens1	11	11	11	---	---
Average daily gain (pounds)	2.28	2.35	2.28	0.04	0.48
Average daily feed intake (pounds)	6.29	6.23	6.20	0.13	0.93
Feed/gain	2.76a	2.65b	2.72a	0.03	0.02
1 Each pen contained 3 boars. a, b Within a row, means with different superscripts differ (P < 0.06) Sources: Organic Sel-Plex; Alltech, Inc., Nicholasville, KY, inorganic (sodium selenite; Premium Selenium 270; North American Nutrition Co., Inc., Lewisburg, OH) sources.

Table 3. Carcass characteristics in control boars and boars fed diets supplemented with 0.3 ppm selenium from organic Sel-Plex or inorganic sodium selenite.
Item:	Control	Sel-Plex	Sodium Selenite	SE	P
No. of boars	11	11	11	---	---
Hot carcass weight, pounds	213.3	214.2	214.1	1.2	0.80
Dressing percent	74.5	74.9	74.9	0.4	0.73
Carcass length, inches	33.7	33.9	33.7	0.03	0.87
Loin muscle area, inches2	9.1	8.7	9.2	0.3	0.38
Backfat thickness, mm
Tenth rib	20.5	19.7	17.2	1.4	0.23
First rib	37.8a	38.2a	33.4b	1.6	0.08
Last rib	21.2	22.2	19.7	1.1	0.30
a, b Within a row, means with different superscripts differ (P < 0.06) Sources: Organic Sel-Plex; Alltech, Inc., Nicholasville, KY, inorganic (sodium selenite; Premium Selenium 270; North American Nutrition Co., Inc., Lewisburg, OH) sources.

In summary, an organic source of selenium (Sel-Plex), which is purportedly more “bio-available” than traditional inorganic sources of selenium (e.g., sodium selenite) failed to alter average daily gain or feed consumption in growing boars, but enhanced feed conversion efficiency during the grower-finisher phase of production. In general, carcass characteristics were not affected by selenium supplementation, although first-rib backfat thickness tended to be decreased in boars fed diets supplemented with sodium selenite compared with un-supplemented boars or boars fed diets supplemented with Sel-Plex. The mechanisms responsible for the effects of different sources of selenium on growth performance and carcass traits in boars remain to be elucidated. Current research at the Tidewater AREC is focusing on the effects of Sel-Plex on semen quality in mature boars used for artificial insemination breeding programs. (This research was funded by grants from Alltech, Inc., the Virginia Pork Industry Board, and the Virginia Agricultural Council).

References

Hansen, J.C. and Y. Deguchi. 1996. Selenium and fertility in animals and man- a review. Acta. Vet. Scand. 37:19-30.

Henson, M.C., H.G. Kattesh, J.P. Hitchcock, and S.A. Kincaid. 1983. The effects of dietary selenium on growth and selected reproductive parameters in young boars. Anim. Prod. 37:401-407.

Jacyno, E., M. Kawecka, M. Kamyczek, A. Kolodziej, J. Owsianny, and B. Delikator. 2002. Influence of inorganic SE + vitamin E and organic SE + vitamin E on reproductive performance of young boars. Agric. Food. Sci. Finland. 11:175-184.

Kolodziej, A. and E. Jacyno. 2005. Effect of selenium and vitamin E supplementation on reproductive performance of young boars. Archiv fur Tierzucht 48:68-75.

Marin-Guzman, J., D.C. Mahan, Y.K. Chung, J.L Pate, and W.F. Pope. 1997. Effects of dietary selenium and vitamin E on boar performance and tissue responses, semen quality, and subsequent fertilization rates in mature gilts. J. Anim. Sci. 75:2994-3003.

NRC. 1998. Nutrient requirements of swine. 10th ed. Natl. Acad. Press, Washington, DC.

Segerson, E.C., W.R. Getz, and B.H. Johnson. 1981. Selenium and reproductive function in boars fed a low selenium diet. J. Anim. Sci. 53:1360-1367.

April 2007