Last month, Pig Progress paid attention to the major vitamins available – what they do and what their functions are in pigs. Among those classified, vitamin E is arguably the most essential for pig production. What does it do?
Vitamin E cannot be synthesised by pigs and is therefore a dietary essential. It is present in natural form in the lipid fraction of feed ingredients, but its functionality is limited as it is susceptible to oxidation. Of all forms of vitamin E, α-tocopherol qualitatively exhibits the highest biological activity. The commercial form of vitamin E for animal feed supplementation is all-rac- α -tocopheryl acetate, an ester which protects α-tocopherol against oxidation.
The functions and metabolism of vitamin E
Vitamin E is primarily known as an efficacious biological antioxidant. Being lipid-soluble and chain-breaking, it protects cellular membranes from being attacked by lipid peroxyl radicals. Vitamin E is actively absorbed in the gut: Absorption depends on a number of factors but, on average, achieves 42% expressed as α-tocopherol equivalents. Vitamin E is transported to the liver, where it is transiently stored. A specific transport protein moves α-tocopherol from the liver into the blood circulation and attaches it to lipoproteins for transport to the various organs and cells. Vitamin E is deposited, in a dose-dependent way, in cellular and subcellular membranes (mitochondria, microsomes), which are rich in fatty acids and thus becomes an integral part of these structural elements, beneficially influencing the fluidity, the structural integrity and the functionality of biological membranes in all cells of the organism.
The physiological importance of vitamin E is much broader than only being an antioxidant, as is explained below.
The majority of symptoms of vitamin E deficiency is related to disorders of the cellular membrane, due to the oxidative degradation of polyunsaturated fatty acids, and can have serious consequences. The deficiency symptoms are specific to each individual animal species. Vitamin E deficiency generally causes liver necrosis and is the reason for several species-specific disorders such as Mulberry Heart Disease, which results in sudden heart failure of pigs. Sub-clinical vitamin E deficiency is hardly detectable but will result in retarded growth and impaired feed conversion as well as diminished fertility, higher susceptibility to infectious diseases, reduced stress resistance and impaired welfare of farm animals.
It has been observed that supra-nutritional supplementation of vitamin E has additive beneficial effects for example on heat stress.
In the next paragraphs more detailed information is provided on benefits of supra-nutritional levels of vitamin E on immune response, reproduction and on meat quality of farm animals.
The role of vitamin E for the functionality of the immune system has been extensively studied by several research groups and is based on the capability of vitamin E to prevent lipid peroxidation in membranes caused by lipid peroxyl radicals. Infectious diseases are an important factor in the production of free radicals for example as a consequence of macrophage function.
Dietary levels of vitamin E ≥ 60 mg/kg were found necessary to attain maximum sow immunologic and reproductive health responses.
As vitamin E transfer through the placenta is very limited, piglets are born with very low levels of α-tocopherol . Colostrum provides a very high concentration of α-tocopherol (more than 20 μg/ml) which permits a considerable increase in tissue concentration of α-tocopherol in piglets during the first few days of their life. Thus it is important through the diet of the sow during the final stages of gestation and during the lactation period to improve the concentration of α-tocopherol in the piglet.
The content in the sow’s plasma and in the milk rises linearly when the concentration of vitamin E in the feed is increased from 70 to 250 mg/kg and this response is maintained throughout lactation. At the time of weaning (at 28 days) the concentration of α-tocopherol in the liver of piglets of which the mothers received 250 mg/kg is more than double than that of piglets from dams receiving 70 mg/kg.
Similarly, a significant variation in E. coli antibodies was measured in piglets born from sows receiving 70, 150 or 250 mg/kg feed of vitamin E: The higher the vitamin E level in sow’s feed, the lower was the need to treat piglets against diarrhoea (see Figure 1). Another key moment in the life of the pig is weaning: the pig’s limited digestive capacity at this stage results in a rapid decline of vitamin E tissue stores, implying a high susceptibility to suffering oxidation processes. It was demonstrated that the inclusion of vitamin E above 100 mg/kg feed and up to 200 mg/kg increase in the serum concentration of α-tocopherol (see Figure 2).
Research studies demonstrated that younger sows experienced higher incidences of reproductive problems associated with inadequate vitamin E than older sows. Some studies carried out in the last few years on breeder sows have demonstrated a positive relationship between vitamin E administration and the number of piglets born.
However, there is some information to indicate that use of vitamin E in the breeder sow goes much beyond improving number of piglets born or survival to seven days. In cattle there is a relationship between vitamin E intake and some problems characteristic of the breeder female, such as retained placentas or the number of somatic cells found in milk. Some of these functions could be affected by deficient production of prostaglandins of which concentration depends on the extent of the oxidative status in animals. The situation is not as clear for the sow, but an increase in the duration of parturition has been shown when vitamin E intake is reduced, which could be due to inadequate contraction of the smooth musculature. A relationship between vitamin E intake and the incidence of mastitis, metritis and agalactia (MMA) has also been shown.
The beneficial effects of including high levels of α-tocopherol acetate in feed on the oxidative stability and sensory quality of meat have been extensively researched in poultry, pork and beef meat. Oxidation processes are responsible for the occurrence of unpleasant smells and flavours, for changes in the nutritive value (reduction in the meat’s polyunsaturated fatty acid and fat-soluble vitamin content) and colour of the meat and even for the appearance of components which are potentially harmful to health, such as cholesterol oxides (COPs).
The amount of published material on all of these aspects is vast and important aspects now seem clear such as optimum levels and period of supplementation and the effects on composition, oxidative stability and sensory quality of the meat.
Oxidative stability of meat
Most of the published studies on vitamin E and meat quality have been aimed at studying its effects on oxidative stability, which in poultry meat is lower than for beef or for pork due to its higher polyunsaturated fatty acid content. Supplementation with high levels of vitamin E is even more important if the fat incorporated in the feed is altered by oxidation or by heat. The risk of oxidation is also increased by the manufacturing processes of meat products (e.g. freezing, mincing, adding salt, pre-cooking or meat irradiation) reducing its vitamin E content and accelerating oxidation, already intense in just three days. Vitamin E supplementation in feed is much more effective in maintaining oxidative stability than adding it to meat post-mortem since by that route it will not be physiologically and naturally incorporated in cellular membranes.
Numerous experiments have shown that supplementation with α -tocopheryl acetate produces a high tissue content of α-tocopherol , leading to an improvement in the oxidative stability of muscle in pigs.
The effectiveness of vitamin E has also been observed in cooked muscle and in the presence of salt. Different studies have further been carried out to investigate the antioxidant effect of vitamin E in relation to the fat composition of the ration. A positive antioxidant effect of vitamin E has been observed when supplemented at 200 mg/kg to pig rations fortified with 3% soy oil and tallow.
As rule of thumb the greater the addition of unsaturated fatty acids, the greater the amount of vitamin E to be administered. There are studies which indicate that supplementing the ration with α-tocopherol inhibits the production of cholesterol oxides (COPs) in heated and refrigerated pork. As previously indicated, the effective level to significantly reduce oxidative stability is equivalent to the inclusion of 100-200 mg of α -tocopheryl acetate per kg feed.
Nutritional value of the meat
In 1975, the researchers Roth and Kirchgessner added α-tocopheryl acetate to the feed at amounts from 5 to 95 mg/kg and found a linear response to vitamin E incorporation in tissues depending on the amount given. Other authors found a logarithmic relationship between the ingestion of vitamin E and the content of α-tocopherol in the various tissues.
These results are in agreement with the data published in the frame of the EU Diet-Ox research project carried out in 1998 which included a total of 14 laboratories: they interchanged data and experiments in which feed fortified with vitamin E was given for at least seven weeks. According to Diet-Ox data the α-tocopherol concentration in muscle tissue should be between 3.5 and 4 mg/kg to have an antioxidant effect. The effective level is equivalent to the inclusion of 100-200 mg of α-tocopheryl acetate per kg feed. These data are in agreement with most of the existing literature and with the most widely used recommendations.
An important aspect of pork meat is its colour, determined mainly by the content and chemical form of the hemin myoglobin pigment. If with storage oxymyoglobin is formed it tends to oxidise and form metmyoglobin causing dark colouration. Supplementation of animal rations with different quantities of vitamin E improves colour stability measured by a lesser reduction in ‘a’ (Minolta system) directly linked to the colour red than found in unsupplemented animals. Data in pigs are less conclusive than with cattle and lambs.
In pigs, it has been observed that when supplementing rations with 100 or 200 mg/kg vitamin E deposition in the longissimus dorsi muscle was 2.6 and 4.72 mg of α-tocopherol /kg which was sufficient to stabilise colour. Tests have shown that it is possible to reduce drip losses through the incorporation of high levels of α -tocopheryl acetate in the ration. Higher α-tocopherol contents in the muscle reduce the passage of biomolecules through cell membranes and therefore the degree of muscle exudation, due to physiochemical interactions of α-tocopherol with molecules in the lipid membrane. The reduction of drip loss has been obtained at levels in the range of 150 to 200 mg/kg of feed of α -tocopheryl acetate. It has been shown that vitamin E accumulated in tissues remains there during processing, improving the technological properties of the meat (e.g. transfer of water) as much as the qualitative attributes of the products like colour stability, acceptability, dryness, presence of unpleasant smells and flavours. It has been possible to observe these effects even in cured products processed for over ten months. Some data indicate that by increasing vitamin E content in feed it is possible to reduce the amount of certain additives included during processing as the meat contains a good quantity of antioxidants at the time of slaughter, bringing benefit to public health and the positive commercial implications associated with it. PP
References available on request.
Source: Pig Progress magazine 29.5 (2013)