Effects of selenium source and level of supplementation on the performance and meat quality of lambs
Introduction
Selenium (Se), in the form of selenocysteine, is the central structural component of a number of specific enzymes, making it an essential trace element for both humans and animals. A number of selenoproteins with known functions have been identified to date and include five glutathione peroxidases (GSH-Px), two deiodinases (Köhrle, 1999), several thioredoxin reductases and selenophosphate synthetase (Behne & Kyriakopoulos, 2001).
The importance of Se is principally associated with its role as an essential part of the glutathione peroxidases (GSH-Px) which provide a defence against oxidative stress by catalyzing the reduction of organic hydroperoxides that react with the selenol group of selenocysteine (Hardy & Hardy, 2004). Consequently an adequate intake of Se is needed to decrease the risk of myopathy, immunodeficiency, cardiovascular disease, cancer and other selenium deficiency syndromes (Hartikainen, 2005). In animals, and particularly in lambs, selenium deficiency has been linked to a number of diseases, which include white muscle disease and suppression of immunity (Rock, Kincaid, & Carstens, 2001). In the Abruzzo region, as in others in Italy, the Se content of plants used in farm animal nutrition is generally low. Consequently health and performance of animals reared on mainly home-grown roughage and grains, which contain low concentrations of Se, may be affected as a consequence of nutritional deficiency.
To date, nutritional Se requirements for lambs have been given as 0.20 mg/kg for lambs growing at 150 g/d (NRC, 2007). Organic Se, in the form of selenomethionine is the predominant Se species in cereals and forage crops. Currently, sodium selenite is the commercial Se source used as a supplement in animal feeds. However, an organic source of Se derived from yeast (Saccharomyces cerevisiae), which contains a high concentration of Se-methionine, has now become commercially accessible following its approval as a feed additive in the USA (Federal Register, 2002) and more recently in the EEC (2006). This alternative source of Se has prompted new research to determine which form of Se supplement would be most efficacious for dietary purposes in farm animal nutrition.
Weiss (2005) indicated that true digestibility of Se from diets containing selenite averages about 50% in sheep, whilst that from Se-yeast would be about 66%. Furthermore, the uptake and assimilation of inorganic Se and Se-methionine are different; inorganic Se is exclusively used for the synthesis of seleno-enzymes and that which is not incorporated into functional enzymes is methylated and subsequently excreted from the body (Deagen, Butler, Beilstein, & Whanger, 1987). On the contrary, Se-methionine is readily incorporated non-specifically into body proteins in place of methionine (Behne, Kyriakopoulos, Scheid, & Gessner, 1991), hence serving as an endogenous Se pool (Rock et al., 2001). Several authors have reported on the correlation between Se content of tissues and muscle GSH-Px activity in a number of different species (cattle - Gatellier, Mercier, & Renerre, 2004; pigs - Daun, Johansson, Önning, & Åkesson, 2001; poultry - Daun & Åkesson, 2004). Thus, Se supplementation may improve the oxidative stability of meat products. However, the effects of organic Se source on the activity of GSH-Px and on the oxidative stability of meat are not well documented. In addition, results on the use of organic Se in the diets of ovine species, and in particular lambs, are limited and need to be developed.
Finally, recommended Se intakes for humans (55 μg/day for adults) are not currently achieved in the majority of European countries (Rayman, 2004, Thomson, 2004). Previous studies have shown that supplementing feed with inorganic Se increased Se concentration in edible tissues of calves (Pavlata et al., 2001, Walsh et al., 1993), lambs (Molnár, Macpherson, & Molnár, 1998), pigs (Goehring, Palmer, Olson, Libal, & Wahlstrom, 1984) and poultry (Leng et al., 2003). The use of organic Se as a possible means of enhancing meat Se content, particularly with selenoamino-acids, has not been largely studied. Concerning this specific subject, a new methodology including capillary HPLC and inductively coupled plasma collision cell mass spectrometry to assess Se-Met and Se-Cyst in serum (Encinar, Schaumlöffel, Ogra, & Lobinski, 2004) and edible tissues (Bierla et al., 2008) has recently been validated.
Therefore, the purpose of this investigation, which was undertaken on Italian light lambs, was to compare the effects of Se-yeast supplementation at different levels to those of an inorganic Se source on animal physical performance, muscle tissue Se concentration, meat quality and shelf-life. Furthermore, a particular purpose was to assess the Se-Met and Se-Cyst content in muscle of treated lambs.
Section snippets
Animals, housing and trial duration
The study was conducted on 48 Italian Apennine lambs. Animals were initially blocked by gender (equal numbers of males and females) and were enrolled at 30 ± 3 days of age with a mean live weight of 12.78 ± 0.94 kg. Animals were randomly allocated to one of four dietary treatments and housed in groups of four animals/pen with 3 pens/treatments. Each pen was bedded with straw and provided a lying area of 1 m2/head. Every pen was provided with fresh potable water in buckets that were cleaned and
Growth rate, feed intake and feed to gain ratio
Average live weight of the animals at completion of the trial was 23.3 ± 2.4 kg, which is consistent with the weight usually achieved by the Apennine breed at the end of its growing period (Lambertini, Morittu, Vignola, Zaghini, & Formigoni, 2005). Growing performance was not influenced by treatment nor were there differences between Se levels or sources. Mean growth rate (Table 3) was 166 ± 33 g/d, as was expected using the diet and calculated allowances used. As expected, a significant effect of
Discussion
Growth performance, feed intake and feed to gain ratio were not influenced either by Se source or level of supplementation. Control group lambs received 0.13 mg/kg DM of naturally occurring Se which was present in the feeds used. In all likelihood results indicate that the Se content of the control diet may have satisfied the requirements for Se of control group lambs. Johansson, Jacobbson, Luthman, and Lindh (1990) previously reported that Se supplementation is not likely to influence growth
References (56)
- et al.
Effects of chemical form and dosage on the incorporation of selenium into tissue proteins in rats
Journal of Nutrition
(1991) - et al.
Chemical forms of selenium in rat tissues after administration of selenite or selenomethionine
Journal of Nutrition
(1986) - et al.
Glutathione peroxidase activity and chemical forms of selenium in tissues of rats given selenite or selenomethionine
Journal of Inorganic Biochemistry
(1988) - et al.
Comparison of glutathione peroxidase activity, and of total and soluble selenium content in two muscles from chicken, turkey, duck, ostrich and lamb
Food Chemistry
(2004) - et al.
Glutathione peroxidase activity, tissue and soluble selenium content in beef and pork in relation to meat ageing and pig RN phenotype
Food Chemistry
(2001) - et al.
Effects of dietary selenite, selenocysteine, and selenomethionine on selenocysteine lyase and glutathione peroxidase activities and on selenium levels in rat tissues
Journal of Nutrition
(1987) - et al.
Fate of selenium from selenite or selenomethionine with or without vitamin E in lambs
Journal of Nutrition
(1967) - et al.
Effect of diet finishing mode (pasture or mixed diet) on antioxidant status of Charolais bovine meat
Meat Science
(2004) - et al.
Selenium: The Se-XY nutraceutical
Nutrition
(2004) Biochemistry of selenium and its impact on food chain quality and human health
Journal of Trace Elements in Medicine and Biology
(2005)