Selenohomoalanthionine improves muscle selenium deposition in pigs

Selenium (Se) is an essential trace element for pigs with its biological effects exerted as part of selenoproteins. There are over 30 identifiable selenoproteins in the body that play key roles in detoxification, immunity and reproduction. Traditional animal feed supplementation of Se has been as sodium selenite, however there is increasing use of organic Se sources such as Se yeast that is predominately selenomethionine. Organic selenium has been shown to significantly increase the deposition of Se into loin muscle (Mahan et al. 1999). The development of new organic Se sources such as selenohomoalanthionine (SeHLan) from different yeast strains has been postulated to be more efficient at incorporation of Se into animal tissue (Tsuji et al. 2010). The hypothesis tested in this experiment was that the incorporation of Se into muscle will be more efficient by the supplementation of SeHLan in the diet of finisher pigs than Se yeast (SeMet) or sodium selenite (SSe), and increased with higher levels of organic Se.

Sixty Primegro commercial immunocastrated male pigs were selected at 16 weeks of age (74.7 kg ± 5.41 kg; mean ± SEM) and housed in individual pens with feed and water available ad libitum. All pigs were offered a commercial grower diet during a 7-day acclimatisation period, after which pigs were individually weighed and randomly allocated to one of five test diets (n = 12) for the next 42 days. All diets contained 13.5 MJ of digestible energy and 7.2 g of standardised ileal digestible lysine. Sodium selenite was added to the first treatment diet to provide 0.3 ppm of added Se. Selenium yeast was added to the second and third treatment diet to provide 0.3 ppm and 0.6 ppm of Se, respectively. SeHLan was added to the fourth and fifth dietary treatments to provided 0.3 ppm and 0.6 ppm of added Se, respectively. Pigs were slaughtered in a commercial abattoir and hot standard carcass weight (HSCW) trim 13 and fat depth at the P2 site were recorded. A 20 g sample of liver was obtained at evisceration and a 50 g sample of loin was taken 24 hours later at boning from each carcass for Se analysis. Data were analysed by ANOVA (IBM SPSS, Version 22.0; USA) with the individual pig as the experimental unit.

There was no difference (P > 0.05) in HSCW or backfat depth at the P2 site between treatments (Table 1). The liver Se levels for pigs fed the 0.3 ppm SSe diet were higher (P = 0.026) than organic sources of Se at the 0.3 ppm inclusion level and similar to the 0.6 ppm inclusion of organic Se sources. The loin Se level was lowest (P < 0.001) for the SSe treatment. The loin Se level increased with the addition of SeMet at the 0.3 ppm level and increased further for the 0.6 ppm of SeMet. The 0.6 ppm SeMet and the 0.3 ppm SeHLan treatments had a similar level of loin Se and was higher by 43% when 0.6 ppm of SeHLan was fed to the pigs.

Table 1.  Hot standard carcass weight (HSCW), backfat depth and selenium (Se) levels in the liver and loin from pigs fed Se from three different sources and at two different levels for the organic sources

Organic Se was incorporated into the loin tissue of the pig more effectively than SSe, and SeHLan was at least 30% more effective than SeMet when included at either 0.3 or 0.6 ppm in finisher diets. The SeMet generally mimics methionine in its metabolism whereas SeHLan may have a different metabolic pathway to incorporation of Se into the muscle which is potentially more efficient.