Evaluating the efficacy of selenium-enriched yeast and sodium selenite on tissue selenium retention and serum glutathione peroxidase activity in grower and finisher swine.

Three experiments conducted with grower-finisher pigs evaluated sodium selenite and a Se-enriched yeast source at various dietary Se levels on Se retention, tissue and serum Se concentrations, and serum glutathione peroxidase (GSH-Px) activity. Experiment 1 was a balance trial conducted in a 2 x 3 factorial arrangement in a randomized complete block (RCB) design in six replicates. Both Se sources were added at .1, .3, or .5 ppm Se. Crossbred barrows (n = 36) averaging 35.9 kg BW were placed in individual metabolism crates and fed their treatment diets, with feces and urine collected for a 7-d test period. Selenium retention increased as dietary Se levels increased, particularly when the Se-enriched yeast was provided, resulting in a Se source x Se level interaction (P < .01). As dietary Se levels increased, urinary Se increased more when pigs were fed sodium selenite, whereas fecal Se increased more when the Se-enriched yeast was fed; both excretion routes resulting in Se level x Se source interaction responses (P < .01). Experiments 2 and 3 were conducted as RCB involving grower (n = 210) and finisher (n = 266) pigs, respectively, and evaluated the two Se sources each at .1, .3, or .5 ppm Se with a non-Se-fortified basal diet serving as a negative control. In Exp. 2, pigs were fed their treatment diets from 22.2 to 60 kg BW in five replicates, whereas in Exp. 3 diets were fed from 65.8 to 105 kg BW in six replicates. Grower pigs fed sodium selenite had serum GSH-Px activity that reached a plateau at .1 ppm Se and .3 ppm when the Se-enriched yeast source was fed, but the interaction response was not significant (P < .15). During the finisher period, serum GSH-Px activity reached a plateau at .1 ppm Se for both Se sources. Serum Se concentrations were lower at .1 ppm Se when the Se-enriched yeast source was fed, resulting in a source x level interaction response for both grower (P < .05) and finisher (P < .01) periods. Loin Se contents were higher in grower and finisher pigs as dietary Se levels increased when the Se-enriched yeast was fed, resulting in a Se source x Se level interaction (P < .01). The results suggest that more Se was retained in muscle tissue when the Se-enriched yeast source was fed, that serum GSH-Px activity reached a plateau at approximately .1 ppm Se, and that sodium selenite may be more biologically available for GSH-Px activity than the Se-enriched yeast source.